Tool reaction balancing mechanism

A tool reaction balancing mechanism consisting of a fluid-pressure reaction and balancing system and an articulated arm wherein the arm is suspended from dual overhead rails by a travelling bridge. The novel articulated arm has two pivotally connected arm sections. One of the arm sections is pivotally mounted at an end of the arm, to a portion of the bridge and the other arm section has means for holding a tool at an opposing end of the arm such that the articulated arm permits a tool fastened in the means for holding a tool to be displaced along a linear path. Biasing means urge the articulated arm toward a rest position wherein the arm sections of the articulated arm are folded in on each other. The novel travelling bridge consists of a main frame unit and a slideable frame unit telescopically connected by a cross beam such that a single trolley which is mounted at the top of the slideable frame unit, and which is engageable with and moveable along a first rail, is able to move in relation to a pair of trolleys which are mounted at the top of the main frame unit, and which are engageable with and moveable along a second rail.

BACKGROUND OF THE INVENTION 
It is now common to provide workers with tool reaction balancing mechanisms 
for holding tools which generate a high degree of torque or vibration and 
which may also have large mass and weight, such as nut-runners and certain 
types of welding equipment, for example. Known tool reaction balancing 
mechanisms typically consist of an arm having a hinge at the middle 
thereof, tool holding means at an end of the arm, and a pressurized-fluid, 
reaction and balancing system operatively connected to the tool holding 
means. 
More particularly, the arm of a known tool reaction balancing mechanism 
generally has a first arm section and a second arm section. The first arm 
section is pivotally mounted at one end to a support member such as to 
swing arcuately therefrom along a first plane, and is hingedly connected 
at its other end to one end of the second arm section. The hinged 
connection between the arm section is adapted to permit the second arm 
section to move arcuately in relation to the first section along a second 
plane substantially at right angle to the plane of first arm section 
movement. The other end of the second arm section has the means for 
holding a tool. 
A principal disadvantage to tool reaction balancing mechanism of the type 
described is that a tool mounted in the holding means at the free end of 
the second section of the mechanism arm is not displaceable linearly along 
either of the two planes at right angle. Yet, especially for assembly line 
operations, a tool is preferably able to be displaced along a linear path 
parallel to a linearly moving work station. 
If desired, the support member to which the arm of a tool reaction 
balancing mechanism is pivotally mounted can be stationary and fixed, such 
as a post. However, in factory applications the arm of the mechanism is 
frequently suspended from overhead tracks or rails by a travelling bridge. 
Prior art travelling bridges generally consist of a rigid cross beam, a 
depending load support beam, a pair of side beams and at least two trolley 
members fastened to each side beam. The side beams are fixedly secured to 
ends of the cross beam at right angle, in an H-shaped frame configuration, 
with the load support beam protruding downwardly from the cross beam 
proximate the middle thereof. The trolley members are each adapted to be 
rollably engageable with a track or rail. 
These bridge structures, having trolley members fastened to the side beams 
of rigid H-shaped frames, are expensive to manufacture and are not 
satisfactory to use when the spaced-apart rails on which the trolley 
members ride are not perfectly parallel, since variances in the distance 
separating the rails along their respective lengths frequently can cause 
the bridge to become stuck. Prior attempts to solve this problem, by 
deliberating introducing play into the trolley members, for example, have 
produced unacceptable side effects, such as bridges which swing from 
overhead rails to an unsafe degree. 
SUMMARY OF THE INVENTION 
The principal object of the present invention is to provide an improved 
tool reaction balancing mechanism and travelling bridge asssembly. It will 
be understood, however, that the example of an improved tool reaction 
balancing mechanism hereinafter illustrated may be used separately from 
the improved travelling bridge, and vice versa. 
The invention accomplishes its objects by providing an articulated arm for 
a tool reaction balancing mechanism which has means for pivotally mounting 
the arm to a support member at one end, which has means for holding an 
object at the other end, and which is configured to permit an object held 
in the holding means of the arm to be displaced along a linear path. More 
particularly, the arm is formed of two pivotally connected arm sections 
having adjustable biasing means urging the arm sections to fold in on each 
other. 
The invention further accomplishes its objects by providing a travelling 
bridge having a three-point, trolley-member connectable with dual, 
spaced-apart overhead rails, instead of the usual four-point 
connectability, thereby reducing the cost of manufacture. The novel 
travelling bridge consists of a main frame unit having two trolleys 
fastened thereto and a slideable frame unit having a single trolley 
fastened thereto. The two trolley members of the main frame unit are 
engageable with and moveable along the first of the overhead rails, and 
the single trolley member of the slideable frame unit is engageable with 
and moveable along the second of the overhead rails. In addition, the 
slideable frame unit is telescopically connected to the main frame unit by 
a telescopic cross beam so that the trolley members are able to move in 
relation to each other to compensate for variances in the distance 
separating the rails along their respective lengths. 
The principles and operation of the present invention will be further 
understood by those skilled in the art by reference to the accompanying 
drawings wherein like numerals designate like or equivalent parts and in 
which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
At FIG. 1 a tool reaction balancing mechanism 10, consisting of a 
fluid-pressure reaction and balancing system 12 and an articulated arm 14, 
is shown with the arm 14 of the mechanism 10 suspended from a pair of 
spaced-apart overhead tracks or rails 16, 18 by a travelling bridge 20. 
The articulated arm 14 of the tool reaction balancing mechanism 10 has a 
first arm section 22 and a second arm section 24, both of which are 
generally tubular and preferably made of metal. Means are provided at one 
end of the first arm section 22 adapted to pivotally mount the first arm 
section 22 to a portion of the travelling bridge 20. As shown, the pivotal 
mounting means is in the form of an open-ended, preferably metallic 
housing 26 fixedly secured, by brazing, welding or other appropriate 
means, to the one end of the first arm section 22, and a preferably 
metallic clevis or yoke 28 fixedly secured to the travelling bridge 20 by 
a plurality of nuts 30 and bolts 32, as set forth in greater detail 
hereafter. Referring now to FIG. 2, a bearing 34 is secured in each end of 
the housing 26. Aligned bores 36, 38 are provided through top and bottom 
walls 40,42 of the yoke 28, a rod 44 is journalled through the bearings 34 
and passed through the aligned bores 36,38 such that a portion 45 of the 
rod 44 is axially disposed within the housing 26, and means are provided 
for retaining the rod 44 through the bearings 34 and bores 36,38, as also 
explained in detail hereafter. 
Means are provided at the other end of the first arm section 22, for 
pivotally connecting the first arm section 22 to an end of the second arm 
section 24. As shown, the pivotal connecting means is identical in 
structure to the pivotal mounting means. An open-ended, preferably 
metallic housing 26' is fixedly secured, by brazing, welding or other 
appropriate means, to the other end of the first arm section 22 and a 
preferably metallic clevis or yoke 28' is fixedly secured proximate its 
top wall 40' to the end of the second arm section 24 in a similar fashion. 
A bearing 34 is secured in each end of the housing 26', aligned bores 
36',38' are provided through top and bottom walls 40',42' of the yoke 28', 
a rod 44' is journalled through the bearings 34 and passed through the 
aligned bores 36',38' such that a portion 45' of the rod 44' is axially 
disposed within the housing 26, and means are provided for retaining the 
rod 44' through the bearings 34 and bores 36',38'. 
The second arm section 24 has two hinged portions 46,48 hingedly connected 
as shown at FIG. 8. Hinged portion 46 of the second arm section 24 is in 
the form of a clevis having aligned bores 50,52 through sidewalls 54 and 
56, respectively. The other hinged portion 48 of the second arm section 24 
is elongated and generally tubular except for a solid swivelling portion 
58 adapted to be fitted within the clevis 46 and having a transverse bore 
60 at one end. A stud or bolt 62 is passed through bores 50,52 and 60 and 
is retained therethrough by a nut 64, for example. A plurality of bearings 
66 are concentrically disposed around the exterior periphery of the bolt 
62 within the bore 60 and a grease fitting 65 is axially fitted in one end 
of the bolt 62. 
Arm section 24, hinged portion 46, and hinged portion 48 will be seen to 
constitute a three portion articulated arm assembly with arm section 24 
comprising a first arm portion, hinged portion 46 comprising a second arm 
portion, and hinged portion 48 comprising a third arm portion. 
The other end of the generally tubular hinged arm portion 48 of the second 
arm section 24 is provided with means for holding an object, such as a 
tool. In the illustrated embodiment, as best shown at FIG. 9, the holding 
means is in the form of a member 67 having a yoke 68 and an integrally 
depending, elongated portion 69 protruding at right angle from a wall of 
the yoke 68. The elongated portion 69 of the member 67 is generally 
tubular and has dimensions enabling it to be slideably engaged within an 
end of the hinged portion 48 of the second arm section 24 with a snug fit, 
FIG. 2. Bolts 70 transversely passed through bores in the elongated 
portion 69 of the holding means member 67 and through aligned bores in the 
hinged portion 48 of the arm section 24, and nuts 72 threaded on the end 
of each bolt 70, retain the elongated portion 69 within the hinged portion 
48. It is apparent that, if desired, a plurality of aligned bores can be 
provided in the hinged portion 48 of the arm section 24 for adjusting the 
distance by which the yoke 68 of the holding means extends beyond the end 
of the arm section hinged portion 48. 
The yoke 68 of the holding means member 67 is further provided with aligned 
bores 76,78 in sidewalls 80,82 for mounting directly therebetween, if 
desired, an object, such as a tool. However, further pivoting or 
swivelling means can be mounted between bores 76,78, as is well known in 
the art, with the tool being secured to such pivoting or swivelling means 
in any appropriate manner. 
An additional aspect of an articulated arm according to the invention is 
biasing means urging the pivotally mounted first arm section 22 to pivot 
in one direction and the pivotally connected second arm section 24 to 
pivot in an opposite direction such that the articulated arm 14 tends to 
fold in on itself as shown in phantom lines at FIG. 10. The biasing means 
also add an aspect of rigidity to the articulated arm 14 when the arm 14 
is extended, to assist a worker in pulling the travelling bridge structure 
20, FIG. 10. 
An example of biasing means for the pivotal mounting means of the first arm 
section 22, and the pivotal connecting means between the first and second 
arm sections, is shown at FIG. 5. The biasing means is in the form of a 
torsion spring 80 concentrically disposed around the rod portion 46 
axially disposed in the housing 26, with one end 79 of the spring 80 being 
affixed within a transverse aperture or slot 82 in the rod portion 46 and 
the other end 83 of the spring 80 being affixed in an angled slot 84 
through a wall 85 of the housing. Identical biasing means are provided for 
the pivotal mounting means of the first arm section 22 and pivotal 
connecting means between the first and second arm sections 22,24 except 
that the torsion spring 80' concentrically disposed around the rod portion 
46' has a right-hand instead of left-hand winding, or vice versa. 
The amount of force applied by the biasing means for the pivotal mounting 
means, and the amount of force applied by the biasing means for the 
pivotal connecting means, are each individually adjustable by rotation of 
the respective rods 44,44'. In other words, rotation of rod 44 winds or 
unwinds spring 80 and rotation of rod 44' winds or unwinds spring 80'. 
Referring again to FIG. 8, the previously mentioned means for retaining 
the rod 44' through the respective bearings 34' and bores 36',38' is also 
adapted to lock each rod 44' in any desired axial position. Rod 44 has 
identical retaining means. In particular, a pair of aligned threaded bores 
86,88 are provided through the top wall 40' of each yoke 28', each 
threaded bore 86,88 opening into the bore 36 holding the rod 44'. Each 
bore 86,88 has an Allen-head bolt 90,92, for example, threaded therein 
with an end of each bolt 90,92 frictionally engaging the exterior surface 
of the rod 44'. The end of each Allen-head bolt 90,92 is tightened against 
the rod 44' after the torsion spring 80' has been wound up to the desired 
degree. To facilitate rotation of either rod 44 or 44', by a lever, for 
example, not shown, a transverse hole 94 is preferably provided proximate 
the top end of each rod 44 or 44', FIG. 2. 
Referring now to the conventional pressurized-fluid reaction and balancing 
system 12, best shown at FIG. 2, a dual-chamber cylinder 96 is fluidly 
connected to a source of compressed fluid 98, such as air, for example, 
through an adjustable regulator valve 100 by conduits 101,103 having 
suitable connections 105 at each end. More particularly, the cylinder 96 
is separated into two chambers 102,104 by a reciprocable piston 106, 
chamber 104 receiving highly pressurized air from source 98 and being at a 
substantially constant air pressure at all times. The pressure of air in 
chamber 102 is substantially atmospheric at all times. A piston rod 108 
protrudes from one side of the piston 106 and extends through an end wall 
107 of the cylinder 96. A member 109 threadably connected to the free end 
of the piston rod 108 by an integral nut 111 is pivotally connected to the 
bottom wall of hinged portion 48 of the second arm section 24 by a 
U-shaped bracket 110. As shown in more detail at FIG. 7, piston rod member 
109 is fastened between the sidewalls 112 of the U-shaped bracket 110 by a 
bolt 114 passed through aligned transverse apertures 116,118 in the 
sidewalls 112 and rod member 109, and by a nut 120 threaded over the end 
of the bolt 114. Bearings 122 are concentrically fitted around the 
exterior periphery of the bolt 114 in the apertures 116 of the bracket 
sidewalls 112, and a grease fitting 123 is axially secured in the bolt 
114. 
The bottom wall 125 of the cylinder 96 has a projecting mounting portion 
124 pivotally connected to a member 126 protruding at right angle from the 
yoke 28' proximate the bottom wall 42 thereof, as shown in detail at FIG. 
6. The mounting portion 124 of the cylinder 96 is solidly cylindrical as 
shown, except for a diametric slot 128. The member 126 protruding from the 
yoke bottom wall 40' is solid and rectangular in cross-section, having 
dimensions enabling it to be inserted in the cylinder mounting portion 
slot 128 with a snug fit. Aligned bores 130,132 are provided in the 
cylinder mounting portion 124 and the yoke protruding member 126. A bolt 
134 is passed through the bores 130, 132 and a nut 136 is threaded over an 
end thereof. Bearings 137 are concentrically disposed around the bolt 134 
in bore 130 and a grease fitting 138 is axially fitted in the bolt 134. 
In use, the fluid-pressure, reaction and balancing system 12 operates in a 
conventional manner to "balance" the hinged portion of arm section 24 by 
normally maintaining same in the "weightless" intermediary position shown 
at FIGS. 1 and 2. The system further provides lift to the hinged portion 
48 of the second arm section 24, and controllably permits the lowering of 
the hinged portion 48, as desired. For example, if the hinged portion 48 
of the second arm section 24 is urged upwardly by a worker wishing to lift 
a tool mounted at the end of the second arm section 24, the piston rod 108 
is pulled upwardly by its pivotal end connection with the bracket 110, the 
piston 106 is slideably displaced toward the top wall 107 of the cylinder 
96 and the volume of pressurized air chamber 104 increases. The pressure 
regulator valve 100 senses the movement of the piston 106, in a manner 
well known in the art, and provides additional pressurized air to the 
chamber 104, thereby helping to lift the hinged portion 48 of the second 
arm section 24 by the piston rod 108. Conversely, if the hinged portion 48 
is controllably urged downwardly by a worker, the piston rod 108 is pushed 
downwardly, the piston 106 is displaced toward the cylinder bottom wall 
125 and the volume of pressurized air chamber 104 progressively decreases. 
The pressure regulator valve 100 again senses the controlled movement of 
the piston 106 and progressively releases pressurized air from the chamber 
104, thereby helping to controllably lower the hinged portion 48 of the 
second arm section. 
However, if the hinged portion 48 is suddenly and uncontrollably jerked or 
tugged toward the cylinder 98, such that piston 106 attempts to move 
rapidly toward the cylinder bottom wall 125, the air in chamber 104 
compressing at a faster rate than it is released, thereby absorbing the 
shock. After the system 12 "reacts" in this fashion, it immediately 
rebalances the hinged arm portion 48 by valve 100 providing air to chamber 
104 to reestablish the substantially constant pressure therein. 
As is also well known in the art, the pressure regulator valve 100 is 
preferably provided with a balance adjusting knob 139 which permits a 
worker to adjust the initial amount of air pressure transmitted to the air 
chamber 104 as a function of the weight of an object mounted at the end of 
the second arm section 24. For convenience of use, the regulator valve 100 
may be directly mounted to the first arm section 22 and connected to the 
conduit 101 by a tubing 137 passed through the first arm section 22. 
Referring now to the travelling bridge structure 20 illustrated at FIGS. 1, 
3 and 4, the bridge 20 has a two piece construction consisting of a main 
frame unit 140 and a slideable frame unit 143 telescopically connected to 
the main frame unit 140 by a telescopic cross beam 141. Two spaced-apart 
conventional, four-roller trolley members 142, engageable with and 
moveable along rail 16, are mounted to the top of the main frame unit 140 
between a set of panels 144,146 by bolts 148 which extend between the 
panels, through aligned bores provided proximate the top of the panels 
144,146 and through a transverse bore 150 in the bottom of each trolley 
member 142. The bolts 148 are locked in position by nuts 152. A single, 
conventional, four-roller trolley member 142', engageable with and 
moveable along rail 18, is mounted to the top of the slideable frame unit 
143, between a set of panels 154,156, in the same manner as the trolley 
members 142 mounted to the top of the main frame unit 140. 
One of the panels 146 of the main frame unit 140 has a cut-out portion and 
one end of an elongated tubular sleeve 158, forming a portion of the 
telescopic cross beam 141, is mounted in the cut-out portion at right 
angle to the panels, 144,146. Another elongated tubular member, in the 
form of a depending load support beam 160, is affixed between the bottom 
of the panels 144,146 and protrudes downwardly therefrom. Two reinforcing 
beams or gussets 162 are angularly affixed between the support beam 160 
and a free, open end 164 of the tubular sleeve 158. 
One of the panels 154 of the slideable frame unit 143 also has a cut-out 
portion with one end 166 of an elongated tubular sleeve 167, forming 
another portion of the telescopic cross beam 141, mounted therein at right 
angle to the panels 154,156. 
Both frame units 140,142, are preferably formed of metal, with the panels 
144,146, tubular sleeve 158, load support beam 160 and gussets 162 of the 
main frame unit 140 brazed or welded together, and with the plates of the 
slideable frame unit 143 brazed or welded to the tubular sleeve 167. 
The telescopic cross beam 141 telescopically connecting the main frame unit 
140 and slideable frame unit 143 is shown in detail at FIGS. 1 and 4. The 
tubular sleeve 167 of the slideable frame unit 142 is dimensioned to 
enable it to be inserted into the open end 164 of the tubular sleeve 158 
of the main frame unit 140 with a finger tight fit therebetween. The 
slideable frame unit tubular sleeve 167 is further provided with a pair of 
spaced-apart, elongated transverse slots 169 having midpoints the same 
distance apart as the midpoints of two sets of aligned bores 170 through 
the main frame unit tubular sleeve 158. A bolt 172, or similar member, is 
passed through each set of aligned bores 170 in the main frame unit 
tubular sleeve 158 and through a corresponding slot 169 in slideable frame 
unit tubular sleeve 167. Nuts 174 are loosely threaded over the end of 
each bolt 172. 
At FIG. 3 it can be seen that the trolley members 142 engageable with and 
moveable along rail 16 are spaced a substantially equal distance apart 
from the trolley member 142' engageable with and moveable along rail 18 so 
that the travelling bridge has a secure, three point connection with the 
rails. Although conventional, four-roller trolley members 142,142' are 
shown in the drawing, it will be understood that any trolley means 
engageable with, and moveable along a rail or track may be substituted. 
At FIGS. 1 and 3 it can also be seen that the bottom of the main frame unit 
depending load support beam 160 has a plurality of mounting holes 176. 
These mounting holes are uniformly spaced-apart a distance corresponding 
to the distance between bores 178 in the rear wall of articulated arm yoke 
26. As previously mentioned, the yoke 26 may be mounted to the support 
beam by nuts 30 and bolts 32, at any desired height and although the 
mounting holes 176 are shown extending upwardly only to the midpoint of 
the load support beam 160, they can be provided across its entire length, 
if desired. 
FIG. 10 illustrates the advantages of the novel tool reaction balancing 
mechanism and travelling bridge assembly by depicting the several 
movements which the assembly makes possible. In the first instance, the 
travelling bridge 20, having two trolley members 142, engageable with and 
moveable along on rail 16 and a single troley member engageable with and 
moveable along on rail 18, permits the entire assembly to travel in either 
direction shown by the arrows without becoming stuck, due to the 
telescopic cross beam 141 telescopically connecting the frame units. The 
articulated arm 14 is normally in the position shown in dotted-line by 
urging of the biasing means. The free end of the articulated arm, having 
means for holding a tool, may be pulled outwardly horizontally to the 
point A, for example, due to the pivotal mounting of the first arm section 
22 and the pivotal connection of the second arm section 24. The free end 
of the articulated arm may then be displaced along a linear path to point 
B, without any movement of the travelling bridge 20. As the free end of 
the articulated arm is displaced to point B, the pivotal connecting means 
moves back toward its rest position, as shown at "X" and the second arm 
section pivots horizontally to the right. Between points B and C, the 
pivotal connecting means moves arcuately away from its rest position to 
point Y. Point D is the point of maximum horizontal linear displacement of 
the free end of the articulated arm which can be accomplished without 
moving the travelling bridge. 
It will be understood that in addition to the linear movements of the free 
end of the articulated arm heretofore described, the articulated arm free 
end can be swung across an arcuate path between points "A" and "D" and can 
also be raised or lowered vertically to the plane of the drawing along the 
hinged connection of the first and second arm sections with an assist from 
the fluid-pressure system, not shown at FIG. 10. 
The embodiment shown in the drawings is merely an example of structure, and 
the scope of the invention is defined by the appended claims.