Welding gun assembly and fluid actuated cylinder

An apparatus for applying a force to a workpiece as required in welding or clamping. The apparatus applies a force to the workpiece through a direct clamping action or through link enhanced scissor type action that increases the mechanical force supplied by a fluid driven cylinder. The fluid driven cylinder has piston rods at both ends of an elongated external housing. The fluid driven cylinder is supported at one end by an attachment to the end of one piston rod and is supported at the other end by an attachment to the external housing. A plurality of pistons permit the piston rods to move relative to one another and also relative to the external housing. The entire fluid driven cylinder can rotate and translate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for performing spot welds 
wherein the apparatus is actuated by a fluid driven cylinder having an 
external housing that can float with respect to a plurality of pistons 
contained within the external housing. 
2. Description of the Prior Art 
The prior art discloses a variety of welding devices that employ a fluid 
driven cylinder to move electrodes into and out of engagement with a 
workpiece. In general, most of the prior art welding assembly devices 
utilize, in conjunction with a single fluid driven cylinder, steel springs 
in order to balance or equalize the electrodes about the workpiece. Some 
prior art devices attempt to balance the electrodes about the workpiece by 
using two fluid driven cylinders to operate the welding gun assembly. 
Whether one cylinder with springs or two cylinders are used to equalize 
the gun, most of these prior art devices mount the body of the fluid 
driven cylinder about a fixed pivot point, while the rod is attached to a 
movable pivot point. The resulting arrangement causes the body of the 
cylinder to oscillate through a relatively large angular sector, therefore 
requiring that the cylinder be mounted a fair distance from the 
transformer or any other fixture component to permit the cylinder to 
oscillate substantially without interfering with any other component 
mounted on the welding gun fixture assembly. In general, most of the prior 
art devices utilize a fluid driven cylinder in which the external housing 
is fixed against axial movement. Such devices rely upon internally 
positioned pistons and attached piston rods to move relative to the fixed 
position external housing. 
The present invention differs from the welding gun that is shown and 
described in U.S. Pat. No. 3,008,033 entitled "Welding Gun" issued Nov. 7, 
1961, to Charles Senn. FIG. 1 of the Senn patent depicts a pair of 
cylinders, one within the other in telescoped fashion. The external 
cylinder has an end closure with a threaded extension for securing the 
welding gun in a fixed position. The internal cylinder houses a fixed 
position piston with an accompanying fixed position piston rod that is 
attached to the end closure of the external cylinder. One end closure of 
the internal cylinder is in the form of an apertured piston that slides on 
the fixed position piston rod. The other end of the internal cylinder 
protrudes from the external cylinder and has attached thereto welding 
electrodes. By regulating the fluid pressure on either side of the 
apertured sliding piston and the fixed piston, the internal cylinder can 
be programmed to move toward and away from a workpiece that is to be 
welded. 
The present invention differs from the above described device in that the 
external housing of the fluid driven cylinder is capable of controlled 
movement under the influence of internally positioned pistons. 
In U.S. Pat. No. 4,137,828 entitled "Welding Gun" issued Feb. 6, 1979, also 
to Charles Senn, there is shown a welding apparatus capable of delivering 
a heavy axial load such as that required for welding concrete reinforcing 
steel. The welding apparatus utilizes inner and outer telescoped 
cylindrical members. The external housing is fixed against axial movement 
and contains an internal cylinder to which welding electrodes are 
attached. The internal cylinder has an apertured end closure that serves 
as a piston. A piston rod fixed to and cantilevered from the attached end 
of the external cylinder passes through the apertured end closure of the 
internal cylinder. The piston rod contains two spaced apart pistons 
attached thereto. The internal cylinder contains a fixed position bulkhead 
that is positioned between the pair of spaced apart pistons. The bulkhead 
has an axially located aperture through which the piston rod can move 
relative thereto. The internal cylinder is driven from within the external 
cylinder under the influence of three air chambers to which air pressure 
is applied simultaneously. The return stroke of the internal cylinder is 
controlled by the application of air pressure to a fourth pressure 
chamber. 
While the present invention does use the fixed bulkhead concept in one 
embodiment, there is no telescoping cylinder arrangement nor is the 
housing containing the pistons of the fluid driven cylinder fixed with 
respect to the workpiece. 
In U.S. Pat. No. 4,684,778 entitled "Resistance Spot Welding Gun and 
Transformer Assembly" issued Aug. 4, 1987, to Dimitrios G. Cecil, there is 
shown and described a spot welding assembly that includes a transformer 
fixed base and a sliding cylinder mounted thereon. As shown in FIG. 5 of 
this patent, the sliding cylinder has a closed end and a centrally 
positioned apertured bulkhead therein. A piston rod is trained through an 
apertured end closure of the sliding cylinder. The piston rod has dual 
pistons attached thereto that lie in chambers on either side of the 
bulkhead that is attached to the sliding cylinder. The piston rod extends 
when air pressure is introduced between the closed end of the sliding 
cylinder and the piston located immediately adjacent thereto. The piston 
rod retracts when air pressure is introduced to the chamber between the 
bulkhead and the aforesaid piston. Thus, there is axial movement of the 
piston in one direction and a reaction movement of the sliding cylinder in 
the other direction. Welding electrodes are attached, respectively, to the 
free end of the piston and a cantilevered U-shaped arm attached to the 
sliding cylinder. The above described device permits welding electrodes to 
be biased in opposed directions toward a workpiece. 
U.S. Pat. No. 3,732,784 entitled "Sequentially Operated Linear Actuator" 
issued May 15, 1973, to Robert A. Vogelei, et al depicts an actuator 
device that employs two cylinder rods that are in axial alignment and 
protrude from opposite ends of an external cylindrical housing. The 
external housing is not adapted for the containment of pressure. 
What is lacking in the prior art is a pincher welding gun assembly which 
utilizes a single fluid driven cylinder without springs, yet provides 
equalization of the electrodes about the workpiece and also restricts 
movement of the fluid driven cylinder to allow a compact, lightweight 
design and assembly of a pincher gun welding assembly. 
SUMMARY OF THE INVENTION 
The present invention is a dual action fluid actuated apparatus for use in 
any application where a generally linear equal and opposite compressive or 
tensile force is applied to a workpiece such as for example in welding, 
forming, and piercing applications. 
The invention is particularly adaptable for use in automated machines such 
as computer controlled robots. When such automated systems are utilized, 
it is important that the machine operate in a repetitive manner with 
little or no malfunction occurring. In order to describe the present 
invention, it will be placed in a welding environment. 
The apparatus includes a compact support framework to which an electrical 
transformer is attached. A fluid driven cylinder is mounted in very close 
proximity to the transformer. The fluid driven cylinder has a piston rod 
extending from one end of the housing which is coupled to the support 
framework while a second piston rod extends from an opposite end which is 
attached to a pair of movable electrode carrying arms. Relative movement 
between the cylinder housing and the piston rods contained therein cause 
link and bell crank coupled electrode arms to move into and out of 
engagement with a workpiece while providing the appropriate equalizing 
feature as well as a midpoint stability of the electrodes. The fluid 
driven cylinder is mounted at one end to a fixed point on the support 
framework and at an opposite end to a moving pivot associated with the 
electrode arms which significantly limits the movement of the cylinder 
thereby permitting the cylinder housing to be mounted in very close 
proximity to the fixture weldments and/or transformer mounting, resulting 
in a more compact arrangement of a pincher type welding gun assembly. 
Another embodiment of the present invention utilizes a floating piston that 
is positioned in contact with one of the piston rods. The floating piston 
enables more accurate equalizing pressure control between the electrodes 
that are coupled thereto. 
An additional embodiment of the invention encompasses not only the floating 
piston but, also, a fixed bulkhead contained within the cylinder body and 
a pair of pistons that are positioned on either side of the bulkhead and 
attached to a common piston rod. The dual pistons connected to a common 
piston rod provide for an amplified power output. 
A primary object of the present invention is to provide a force generating 
multi-action apparatus that is compact and can function with a variety of 
tools attached thereto. 
Another object of the present invention is to provide a fluid driven 
apparatus over which the movement thereof can be accurately controlled. 
A further object of the present invention is to provide a fluid driven 
cylinder that can move relative to the axial movement of piston rods 
contained therein. 
Another object of the present invention is to reduce the distance between 
the transformer and the fluid driven cylinder. 
Still another object of the present invention is to produce a nearly 
balanced loading on the workpiece. 
A further object of the present invention is to utilize a fluid driven 
cylinder that provides limited pivoting movement to permit the cylinder to 
be mounted near the transformer, resulting in a more compact assembly. 
Another object of the present invention is to provide a welding apparatus 
that can be hydraulically driven into contact with the workpiece as well 
as hydraulically driven away therefrom. 
An additional object of the present invention is to provide midpoint 
rigidity to the movement of the electrodes attached to the apparatus. 
A yet further object of the present invention is to provide forward and 
rear piston rods with pinned connections. 
Further objects and advantages of the present invention will become 
apparent from the following description and the appended claims, reference 
being made to the accompanying drawings forming a part of this 
specification, wherein like reference characters designate corresponding 
parts in the several views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and more particularly to FIG. 1, there is 
illustrated in perspective an apparatus of the present invention in the 
form of an electrical spot welder. The tool shown in FIG. 1 is adapted 
particularly for attachment to the arm of an industrial robot that would 
find use in industry such as automobile assembly lines. 
With reference to FIG. 1, the overall apparatus is represented by the 
numeral 20. A box-like cradle or frame support structure 22 is assembled 
by welding or in the alternate with bolts. The support structure 22 has a 
bottom plate 24 and a top plate 26 that are positioned in generally 
parallel relationship to one another. A back plate 28 is positioned 
between the top plate 26 and the bottom plate 24. Spaced apart side plates 
30 and 32 are attached to the bottom plate 24 and the back plate 28. An 
electrical transformer 34 is attached to the top plate 26 by a plurality 
of bolts 36, as best seen in FIG. 3. The electrical transformer 34 can, by 
way of example, be a 32 KVA transformer that operates on a single phase 
440 volt, 50-60 hertz input which is coupled to the primary coil of the 
transformer 34. The overall apparatus 20 has an upper yoke 38 and a lower 
yoke 40 to which a pair of shunts 42 and 44 are, respectively, attached. 
The shunts 42 and 44, similar to the upper and lower yokes 38 and 40, are 
constructed from a good electrical conductor such as copper. Since the 
shunts 42 and 44 are required to undergo repetitive flexing, they are 
essentially U-shaped leaf springs each consisting of a plurality of very 
thin copper sheets. The shunts 42 and 44 are, of course, attached to the 
secondary output terminals of the electrical transformer 34. The upper 
yoke 38 has attached thereto an elongate electrode 46, and a similar 
elongate electrode 48 is attached to the lower yoke 40. The electrodes 46 
and 48 are curved at their terminal ends so that they can contact opposing 
faces of a workpiece 50. The electrodes 46 and 48 are hollow in 
construction to permit the ingress and egress of a cooling fluid such as 
water. The upper and lower yokes 38 and 40 are actuated by a fluid driven 
cylinder 52 that is positioned within the support structure 22. A brief 
description of the fluid driven cylinder 52 is set forth immediately 
below. 
FIG. 2 is a perspective view of the fluid driven cylinder 52 that provides 
mechanical power for the overall apparatus 20. The fluid driven cylinder 
52 has a rear cylinder head 54 and a front cylinder head 56 that are in 
spaced apart parallel orientation. A bulkhead 58 is positioned between the 
rear and front cylinder heads 54 and 56. A rear cylinder body 60 is 
positioned between the rear cylinder head 54 and the bulkhead 58. In a 
similar manner, and in axial alignment therewith, a front cylinder body 62 
is positioned between the bulkhead 58 and the front cylinder head 56. The 
front and rear cylinder heads 56 and 54, the bulkhead 58, and the front 
and rear cylinder bodies 62 and 60 are coupled together by a plurality of 
tie rods 64 that pass through apertures in the rear cylinder head 54 and 
the bulkhead 58 and are anchored in the front cylinder head 56 by a 
threaded engagement. The assembly of the just mentioned parts of the fluid 
driven cylinder 52 forms an external housing 65. A reaction piston rod 66 
is shown as it extends outside of the rear cylinder head 54. The reaction 
piston rod 66 is in axial alignment with the longitudinal axis of the 
fluid driven cylinder 52. The reaction piston rod 66 and a front piston 
rod 68 have longitudinal axes that are coincident with each other. A 
double apertured link 70 is attached to the free end of the front piston 
rod 68. A clevis 72 with an aperture 74 through the legs thereof is 
positioned on each side of the front piston rod 68. The details of the 
fluid driven cylinder 52 will be explained more fully below. 
FIG. 3 is a side elevational view that shows the electrical transformer 34 
mounted immediately above the fluid driven cylinder 52 to maintain a 
compact assembly. The transformer 34 is attached to the top plate 26 by a 
plurality of bolts 36. As best seen in FIG. 5, the side plates 30 and 32 
are of symmetrical configuration and each contain an elliptical aperture 
78 that permits access to the fluid driven cylinder 52 which is contained 
within the support structure 22. The side plates 30 and 32 have 
cantilevered support arms 80 and 82 that extend in a forward and upward 
direction. The support arms 80 and 82 have bores 84 and 86 that are in 
axial alignment with each other. A pivot pin 88 is supported within a pair 
of flange bearings 90 and 92 which are installed in the bores 84 and 86. 
The pivot pin 88 and its function will be discussed in more detail below. 
The back plate 28 of the support structure 22 has a pair of spaced apart 
brackets 94 and 96 that are positioned on each side of a centrally located 
aperture 98 in the back plate 28, as shown in FIG. 4, and the brackets 94 
and 96 are attached to the back plate 28 by a series of bolts 102. The 
brackets 94 and 96 each contain a bore 100 which are in axial alignment 
with each other and into which a pivot block 104 is journaled. The pivot 
block 104 provides the sole support for the rear portion of the fluid 
driven cylinder 52. 
Attention is now directed to the upper yoke 38 which supports the electrode 
46. An upper yoke end 106 contains a clamp arrangement for the 
immobilization of the electrode 46. Bolts 108 provide the clamping force 
necessary for complete immobilization of the electrode 46. The upper yoke 
38 is partially cored for the conveyance of a cooling fluid such as water 
therethrough. A fluid ingress port 110 is in communication with the 
interior of the electrode 46. A fluid egress port 112 receives the outflow 
of the cooling fluid from the electrode 46. The upper yoke 38 is 
bifurcated into two widely spread apart legs 114 and 116, as best seen in 
FIG. 5. The apex of the bifurcation occurs at approximately the broken 
line 118, as shown in FIG. 3. The upper yoke 38 has a boss 120 that serves 
as the attachment point for the shunt 42. 
The lower yoke 40 has a clamp arrangement for securing the electrode 48. 
Bolts 122 generate the clamping force necessary for the containment of the 
electrode 48. The lower yoke 40 has a fluid ingress port 124 that is in 
communication with the interior of the electrode 48 and the outflow of the 
cooling fluid passes through a fluid egress port 126. The lower yoke 40 
has an upwardly extending arm 128 that is clamped to the pivot pin by a 
bolt 130 and has a boss 131 to which the shunt 44 is attached. A bore 133 
passes through the upwardly extending arm 128 as shown in FIG. 5. The 
lower yoke 40 has a downwardly extending clevis 132 adjacent to the 
electrode 48 which has a bore 134 through both legs thereof for the 
accommodation of a pin 136. An adjustable rod 138 is retained at one end 
by the pin 136 and at the opposite end the adjustable rod 138 is retained 
by a pin 140 that is coupled to the lower ends of spaced apart yoke links 
142 and 144. The profile of the yoke link 142 can be seen in FIG. 3A. The 
pin 140 is created by two bosses machined cylindrically on a cube-shaped 
yoke through which passes the adjustable rod 138. The cylindrical bosses 
or pin 140 is journaled in a pair of bores 146 and 148 in the yoke links 
142 and 144 and the yoke links 142 and 144 also have a centrally 
positioned bore 147 that accommodates a pin 150. The pin 150 also passes 
through an aperture 76 in the outboard end of the link 70 (shown in FIG. 
7) which is attached to the front rod 68 of the fluid driven cylinder 52. 
The yoke links 142 and 144 have a bore 153 positioned at the top end to 
contain the pivot pin 88. 
FIG. 4 is an elevational end view facing the left-hand side of FIG. 3. The 
shunts 42 and 44 are shown at the top of FIG. 3. A shunt adapter 154 
connects the shunt 42 to the electrical transformer 34. In a similar 
manner, a shunt adapter 156 connects the shunt 44 to the electrical 
transformer 34. The back plate 28 of the support structure 22 contains the 
centrally positioned aperture 98 as well as four additional apertures 158 
which permit access to the tie rods 64 and also provide weight reducing 
holes in the back plate 28. An appropriate access aperture (not shown) is 
also provided in the back plate to permit access to a fluid port or bore 
310. The brackets 94 and 96 are anchored to the back plate 28 by the bolts 
102. The pivot block 104 is journaled in the bores 100 and, as previously 
mentioned, provides the sole support for the rear portion of the fluid 
driven cylinder 52. The pivot block 104 contains a centrally located bore 
160 that is in axial alignment with the longitudinal axis of the fluid 
driven cylinder 52. 
FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 3 which 
shows the pivot pin 88 and the associated components that are journaled 
thereon. The pivot pin 88 is supported by the flange bearings 90 and 92 
which are seated in the bores 84 and 86 of the side plates 30 and 32. The 
downwardly extending legs 114 and 116 of the upper yoke 38 have centrally 
positioned intermediate bosses 162 and 164 through which bores 166 and 168 
are located. The bores 166 and 168 contain the pivot pin 88. The legs 114 
and 116 also have lower extensions 170 and 172 which have end bosses 174 
and 176 that accommodate bores 178 and 180. The bores 178 and 180 contain 
pins 182 and 184 that couple the end bosses 174 and 176 to the pair of 
clevises 72 that are attached to the front cylinder head 56 of the fluid 
driven cylinder 52. The pins 182 and 184 support the front half of the 
fluid driven cylinder 52. 
FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 3 that shows 
the adjustable rod 138 and its end connections. The pin 140 is shown 
within the bores 146 and 148 of the yoke links 142 and 144. The bore 134 
through both legs of the clevis 132 contains the pin 136. 
FIG. 7 is a cross-sectional side view of the fluid driven cylinder 52 taken 
axially through the cylinder which is shown in perspective in FIG. 2. The 
fluid driven cylinder 52 has the centrally positioned bulkhead 58 as well 
as the front and rear cylinder head 56 and 54 that are held in spaced 
relationship by the front and rear cylinder bodies 62 and 60. The rear 
cylinder head 54 has a cylinder head bearing 186 that is positioned in an 
axially aligned bore 188 and held in position by a retaining ring 190. The 
reaction piston rod 66 is threaded at its end 192 for engagement with the 
pivot block 104, as shown in FIG. 3. The reaction piston rod 66 has a 
reduced diameter section 194 that contains a reaction piston 196 flanked 
by washers 198 and 200. A sleeve 202 is placed over the reduced diameter 
section 194 in abutment with the washer 200. A piston stop 204 is placed 
in abutment against the ends of the reaction piston rod 66 and the sleeve 
202. The reaction piston rod 66, the washers 198 and 200, the sleeve 202, 
and the piston stop 204 are locked together as a unit by the installation 
of a bolt 206 in a threaded bore 208 in the end of the reaction piston rod 
66. The reaction piston rod 66 has an axially aligned bore 210 that 
commences at the threaded end 192 and ends at radially aligned bores 212 
and 214. The sleeve 202 contains notches (not shown) at its end adjacent 
to the washer 200 so as not to impede access to the ends of the radially 
aligned bores 212 and 214. A floating piston 216 that contains an axially 
aligned bore 218 is positioned over the sleeve 202 so that it is in 
sliding engagement therewith. The floating piston 216 has an impact plate 
220 attached to one face by a plurality of bolts 222. 
The front piston rod 68 consists of a rear piston rod section 224 and a 
forward piston rod section 226. The rear piston rod section 224 has a 
partially threaded reduced diameter section 228 and an intermediate 
diameter section 230. A shoulder 232 is formed at the junction of the 
reduced and intermediate diameter sections 228 and 230. A rear piston 234 
is positioned on the reduced diameter section 228 in abutting contact with 
the shoulder 232. A threaded nut 236 is engaged with the reduced diameter 
section 228 to lock the rear piston firmly into engagement with the 
shoulder 232. The intermediate diameter section 230 is trained through a 
bore 238 in the bulkhead 58. The front end, or right end as viewed in FIG. 
7, of the rear piston rod section 224 terminates with a flange 240 of 
greater diameter than the intermediate diameter section 230. The rear 
piston rod section 224 contains a large axially aligned bore 242 that 
permits the piston stop 204 of the reaction piston rod 66 to move freely 
therein. Two radially aligned bores 244 and 246 are positioned in the 
intermediate diameter section 230 so that they intersect the axially 
aligned bore 242. 
The forward piston rod section 226 is in the form of a sleeve with an 
external diameter 248. The forward piston rod section 226 has an internal 
bore 250 that terminates at its forward end with a shoulder 252 that is 
adjacent to a smaller diameter bore 254. A link adapter 256 is contained 
within the internal bore 250 with its forward end abutting the shoulder 
252. The flange 240 of the rear piston rod section 224 fits into the 
internal bore 250 of the forward piston rod section 226 so that it is in 
contact with the link adapter 256. A forward piston 258 is positioned on 
the intermediate diameter section 230 of the rear piston rod section 224 
adjacent to and in contact with the flange 240. The forward piston 258 is 
also in abutting relationship with an end 260 of the forward piston rod 
section 226. A series of bolts 262 are utilized to attach the forward 
piston 258 to the end 260 of the forward piston rod section 226. The 
installation of the bolts 262 firmly lock together the rear piston rod 
section 224, the forward piston rod section 226, the forward piston 258, 
and the link adapter 256. 
The front cylinder head 56 consists of two parts, a retainer 264 and a 
piston rod bushing 266. The retainer 264 contains as an integral part 
thereof the two clevises 72 shown in FIG. 2. A vent 268 is threaded into a 
bore 270 that passes through the wall of the retainer 264. The retainer 
264 also has an internal bore 272 that is in axial alignment with the 
overall apparatus 20. A slightly larger diameter bore 274 is positioned 
adjacent to the bore 272 and a radially disposed wall 276 interconnects 
the bores 272 and 274. The piston rod bushing 266 has an internal bore 278 
through which the forward piston rod section 226 passes and also has a 
radially extending flange 280 that fits into abutment against the radially 
disposed wall 276 of the retainer 264. A plurality of circumferentially 
spaced apart bolts 282 clamp the retainer 264 and the piston rod busing 
266 together. 
Returning once again to the bulkhead 58, a partially threaded bore 284 is 
positioned in the exterior wall of the bulkhead 58. An intercepting bore 
286 connects the bore 284 with a chamber 288. Another partially threaded 
bore 290 is positioned in the exterior wall of the bulkhead 58. An 
intercepting bore 292 connects the threaded bore 290 with a chamber 294 
which is positioned between the forward face of the bulkhead 58 and the 
rear surface of the forward piston 258. The chamber 294 is in 
communication with a chamber 296 located in the intermediate diameter 
section 230 of the rear piston rod section 224 via the radially aligned 
bores 244 and 246. The bulkhead 58 contains a recess 298 to accommodate a 
boss 300 on the rear piston 234. This arrangement permits the rear piston 
234 to move into close engagement with a rear wall 302 of the bulkhead 58. 
A forward wall 304 of the forward piston 258 and the front cylinder head 
56 define a chamber 308. 
The rear cylinder head 54 contains the threaded bore or fluid port 310 in 
the exterior wall thereof. The threaded bore is in communication with a 
chamber 312 which is positioned between the forward wall of the rear 
cylinder head 54 and the rear face of the reaction piston 196. The bore 
210 and the radially aligned bores 212 and 214 are in communication with a 
chamber 314 that is positioned between the forward face of the reaction 
piston 196 and the rear face of the floating piston 216. An additional 
chamber 316 is positioned between the forward face of the floating piston 
216 and the rear face of the rear piston 234. The chamber 316 is in direct 
communication with the chamber 296. 
FIG. 8 is a top plan view of the fluid driven cylinder 52 which shows the 
tie rods 64 in a clamped position. The tie rod 64 has a wrenching head 318 
adjacent the rear surface of the rear cylinder head 54. The opposite end 
of the tie rod 64 has a threaded end 320 that mates with a threaded bore 
322 in the front cylinder head 56. 
FIG. 9 is an elevational view of the right-hand end of the fluid driven 
cylinder 52 shown in FIGS. 2, 7, and 8. Corners 324 of the rear cylinder 
head, the bulkhead 58, and the front cylinder head 56 are chamfered to 
reduce the weight of the overall fluid driven cylinder assembly. The link 
70 is shown in the center of the forward piston rod section 226. A pin 326 
is contained in the link adapter 256, as best seen in FIG. 7. 
FIG. 10 is a cross-sectioned view taken along line 10--10 of FIG. 7 which 
shows the forward piston rod section 226 and the link adapter 256. The pin 
326 is contained in a bore 328 and the pin 326 has an axially extending 
bore 330 that contains insulating end caps 332. 
Throughout the discussion and description of the invention presented above, 
it is assumed that those skilled in the art are aware that certain 
insulative materials have to be utilized between some adjacent components 
in order to assure the integrity of the electrical system. Also, seals 
such as O-rings have been shown but not individually identified. 
ASSEMBLY AND OPERATION 
The assembly of the present invention is very straightforward. The cylinder 
head bearing 186 is installed in the rear cylinder head 54. The reaction 
piston rod 66 is pushed through the cylinder head bearing 186. The 
reaction piston 196, the washers 198 and 200, the floating piston 216 with 
its impact plate 220, and the sleeve 202 are then placed in proper 
position on the reaction piston rod 66. The piston stop 204 is placed on 
the bolt 206 which is then threaded into the threaded bore 208 in the end 
of the reaction piston rod 66. The rear cylinder body 60 is then 
positioned over the reaction piston 196 and the floating piston 216. The 
above subassembly is then set aside. 
A separate subassembly is made of the link 70, the pin 326, the link 
adapter 256, the front piston rod 68, the rear piston rod section 224 and 
the forward piston 258. This may be accomplished by aligning the link 70 
with the bore 328 in the link adapter 256 and inserting the pin 326 to 
firmly attach the link 70 to the link adapter 256. The link adapter 256 
with the link and pin installed is then inserted in the bore 250 of the 
front piston rod 68. The flange 240 of the rear piston rod section 224 is 
placed into abutting relationship with the end of the link adapter 256. 
The forward piston 258 is then pushed onto the intermediate diameter 
portion of the rear piston rod section 224 until it abuts the forward 
piston rod section 226 of the front piston rod 68 and then bolted in 
placed using the bolts 262. This separate subassembly is then mounted to 
the bulkhead 58 and the rear piston 234 by pushing the rear piston rod 
section 224 through the bulkhead 58 and thereafter mounting the forward 
piston 258 on the reduced diameter section 228 of the rear piston rod 
section and securing the rear piston thereto by way of the nut 236. 
The previously set aside rear portion subassembly is then moved into axial 
alignment so that the front end of the reaction piston rod 66 enters the 
axially aligned bore 242 in the rear piston rod section 224. The tie rods 
64 are then installed to hold the fluid driven cylinder 52 together as a 
working unit. 
The assembled fluid driven cylinder 52 is positioned within the support 
structure 22. The pivot block 104 is installed on the threaded end 192 of 
the reaction piston rod 66. The brackets 94 and 96 are positioned on the 
ends of the pivot block 104 and then bolted to the back plate 28 with the 
bolts 102. The electrical transformer 34 is installed on the top plate 26 
of the support structure 22 by the bolts 36. The pivot pin 88 is trained 
through the bores 84 and 86 of the support arms 80 and 82, the bores 166 
and 168 in the upper yoke 38, the bores 153 in the yoke links 142 and 144, 
and the bore 133 in the upwardly extending arm 128 of the lower yoke 40. 
The lower yoke 40 is then clamped to the pivot pin 88 by the bolt 130. The 
pin 150 is then inserted through the bores 147 in the yoke links 142 and 
144 and through the bore 152 in the link 70. The pins 182 and 184 are then 
inserted through the clevises 72 and the bores 178 and 180 of the upper 
yoke 38. The adjustable rod 138 is attached to both lower ends of the yoke 
links 142 and 144 with the pin 140. The other end of the adjustable rod 
138 is then coupled to the clevis 132 on the lower yoke 40 with the pin 
136. The shunt adapters 154 and 156 are then attached to the electrical 
transformer 34. The shunts 42 and 44 are coupled between the shunt 
adapters 154 and 156 and the respective shunts 42 and 44. The electrodes 
46 and 48 are inserted into the upper and lower yokes 38 and 40. Fluid 
connections for cooling and operation, including additional electrical 
connections, may then be completed. After assembly, the fluid driven 
cylinder 52 is in an operating attitude, that is, it is completely 
suspended within the confinement of the support structure 22 but not in 
contact with it. The fluid driven cylinder 52 is pivotally supported at 
the rear entirely by the pivot block 104 and in the front the entire 
support is provided by the coupling to the upper yoke 38. Thus, the 
external housing 65 of the fluid driven cylinder 52 can translate and 
rotate relative to the surrounding support structure 22. Also, the 
external housing 65 can move relative to the reaction piston rod 66 and 
the front piston rod 68. 
The present invention will work equally well with a scissor or bell crank 
system which has been described above, or with a linear system which will 
now be set forth during an explanation of the operation sequences of the 
embodiments of the invention. 
FIG. 11 is a schematic side view of a single stroke clamping and equalizing 
cylinder with attached electrodes 46 and 48 in an open position with 
respect to a workpiece 50. Fluid pressure is applied to the chamber 312 
causing the external housing 65 to move to the left, as viewed in FIG. 11, 
since the reaction piston rod 66 is held in fixed position. As the 
external housing 65 moves to the left, the electrode 46 approaches the 
workpiece 50. Fluid pressure is then introduced to the chamber 316, acting 
on the rear piston 234 which causes it to move to the right. As the rear 
piston 234 moves to the right, the front piston rod 68 advances the 
electrode 48 towards the workpiece 50 to clamp the workpiece. 
FIG. 12 is a schematic side view which shows the electrodes 46 and 48 in a 
closed position with respect to the workpiece 50. Since the effective 
working area of the reaction piston 196, as it faces the chamber 312, is 
less than the area of the rear piston 234 area facing the chamber 316, the 
respective fluid pressures may have to be balanced so that undue force is 
not applied to the workpiece by either of the electrodes 46 or 48. After 
the weld sequence has been performed, the fluid pressure is released in 
the chambers 312 and 316 and fluid pressure is applied to the chamber 288. 
The pressure reaction against the face of the rear piston 234 causes the 
front piston rod 68 to move away from the workpiece 50. When the rear 
piston has moved its maximum distance to the left, the external housing 65 
will move to the right, moving the electrode 48 away from the workpiece 
50. The chamber 288 is vented as the robot is moved to its next work 
position to begin the next weld sequence and the weld cycle is ready to 
start again. 
FIG. 13 is a schematic side view of a second embodiment of the present 
invention which sets forth a double stroke clamping and equalizing 
cylinder which provides electrodes 46 and 48 in an open position with 
respect to the workpiece 50 as well as a midpoint position. In this 
embodiment of the invention, the floating piston 216 has been installed on 
the forward section of the reaction piston rod 66. During the initial 
start position, the electrodes 46 and 48 are at their maximum distance 
from the workpiece 50. Also, in the start position, as shown, the external 
housing 65 is advanced its maximum toward the right, as viewed in FIG. 13. 
The floating piston 216 and the rear piston 234 are in close proximity to 
the reaction piston 196. 
FIG. 14 is a schematic side view similar to that shown in FIG. 13 except 
that the electrode 48 has moved to an intermediate position toward the 
workpiece 50. Fluid pressure is applied to the chamber 314, moving the 
floating piston 216 into abutting relationship with the rear piston 234. 
The floating piston 216 and the rear piston 234 move in unison toward the 
right until the floating piston 216 reaches its stop position against the 
piston stop 204. The advancement of the rear piston 234 to the right 
carries the electrode 48 to an intermediate position with respect to the 
workpiece 50. 
FIG. 15 is a schematic side view that shows the electrodes 46 and 48 in 
contact with the workpiece 50. To arrive at this position from the 
intermediate position set forth above, the fluid pressure in the chamber 
288 is exhausted and maintained in the chamber 314. Fluid pressure is then 
applied to the chambers 312 and 316. The rear piston 234 moves to the 
right causing the electrode 48 to contact the workpiece 50. At the same 
time, the external housing 65 moves to the left bringing the electrode 
into contact with the workpiece 50. After the weld has been performed on 
the workpiece 50, the electrodes 46 and 48 can be returned to the 
intermediate position by releasing the fluid pressure in the chambers 312 
and 316, and by applying fluid pressure to the chamber 288 which causes 
the rear piston 234 to move to the left and the external housing 65 to 
move to the right. The electrodes 46 and 48 can be moved to the fully 
open, or start position, by venting the fluid pressure from the chamber 
314. 
FIG. 16 is a schematic side view of a third embodiment of the present 
invention which shows a multiple piston high force generating system with 
the electrodes 46 and 48 in the open position with respect to the 
workpiece 50. In this concept of the invention, the bulkhead 58 is 
attached to the external housing 65 to the right of the rear piston 234. 
The forward piston 258 is attached to the front piston rod 68 between the 
bulkhead 58 and the right end of the external housing 65. The initial 
start position is shown in FIG. 16 with the reaction piston 196, the 
floating piston 216, and the rear piston 234 all to the left in close 
proximity to the left end of the external housing 65. 
FIG. 17 is a schematic side view similar to that shown in FIG. 16 except 
that the electrode 48 has moved to an intermediate position with respect 
to the workpiece 50. The electrode 48 arrives at its intermediate position 
by introducing fluid pressure to the chamber 314 causing the floating 
piston 216 to move to the right, carrying the rear piston 234 to the 
right. The pressure in the chamber 314 is maintained at this time. 
FIG. 18 is a schematic side view that shows the electrodes 46 and 48 in 
contact with the workpiece 50. Fluid pressure is then applied to the 
chambers 312 and 316 as well as the chamber 294. The chambers 316 and 294 
can be pressurized from a common source. The force exerted by the 
electrodes 46 and 48 is increased considerably because of the increase in 
area provided by the combination of the rear piston 234 and the forward 
piston 258 acting in unison. During the advancement of the forward piston 
258 toward the right the chamber 308 is vented to the atmosphere. The 
electrodes 46 and 48 are returned to an intermediate or midpoint position 
by removing the pressure from the chambers 312, 316 and 294 and applying 
pressure to the chamber 288. The electrodes 46 and 48 are then returned to 
a full open position by removing the pressure from the chamber 314 and 
maintaining pressure to the chamber 288. 
The pressurizing and venting of the chambers heretofore discussed in 
describing the operation of the various embodiments of the invention can 
be accomplished by the utilization of two-way and three-way valves as is 
readily apparent to those skilled in the art. Additionally, the term fluid 
pressure has been referred to throughout the discussion. Such terminology 
applies equally well to liquids such as oil and to gaseous mediums such as 
air. 
While the illustrative embodiment of the invention has been described in 
considerable detail for the purpose of setting forth practical operative 
structures whereby the invention may be practiced, it is to be understood 
that the particular apparatus described is intended to be illustrative 
only, and that the various novel characteristics of the invention may be 
incorporated in other structural forms without departing from the spirit 
and scope of the invention defined in the appended claims.