Shock absorber with stop collar

A shock absorber assembly of the so-called primary type in which the outer cylinder includes a central main body smooth walled cylindrical portion and reduced diameter threaded portions are provided at each end of the main body portion for mounting purposes. The assembly of the invention includes a stop collar which is adapted to be threaded onto the front reduced diameter threaded portion of the shock absorber and which has a length which is precisely dimensioned relative to the effective length and stroke of the shock absorber such that the object hitting the impact pad of the shock absorber will encounter the front annular edge of the stop collar just prior to bottoming of the piston of the shock absorber against the end wall of the cylinder. In front mount installations, the length of the stop collar is slightly greater than the length of the reduced diameter front portion of the cylinder plus the effective length of the shock absorber minus the prescribed thickness of the front mounting bracket and minus the stroke of the shock absorber cylinder. In rear mount installations, the length of the stop collar is slightly greater than the length of the front reduced diameter portion plus the effective length of the shock absorber minus the stroke of the shock absorber.

BACKGROUND OF THE INVENTION 
This invention relates to a shock absorber device for linearly decelerating 
a machine part by imposing a relatively constant force on the part over 
the stroke of the device. 
Shock absorbers which force fluid through a restricted orifice to convert 
the kinetic energy of a moving part into an increase in the thermal energy 
of the fluid are commonly used on machines. The smoothest deceleration of 
the moving part is obtained by absorbers which offer a constant resistive 
force to the motion over the total duration of the deceleration. 
In a typical installation, a machine tool or transfer arm is repetitively 
moving back and forth between separate operating positions and the 
movement of the tool or arm as it arrives at each position is cushioned 
and decelerated by a shock absorber positioned on the tool or arm or on 
the adjacent supporting structure. Ideally, as the tool or arm is 
decelerated at each end of its reciprocal movement, the shock absorber 
acts to exert a constant resistive force against the tool and smoothly 
decelerates the tool to a stop position in which the piston of the shock 
absorber has traversed substantially the entire length of the cylinder of 
the shock absorber so as to take advantage of the entire range of the 
fluid orifice means typically provided along the cylinder, and the piston 
comes to a stop just shy of the end of the cylinder so as to avoid 
destructive bottoming of the piston against the end of the cylinder. Since 
it is difficult to obtain these ideal deceleration conditions, and since 
it is further desirable to provide a positive delimiting means to 
establish the extent of movement of the tool or arm in each direction of 
reciprocal movement, it is common practice to employ a stop member at each 
end of the movement of the tool or arm against which the tool or arm comes 
to rest as the tool arrives at the end of its movement. Ideally 
positioned, the stops provide proper end limit positions for the tool or 
arm, avoid bottoming of the piston against the end of the cylinder to 
preclude damage to the shock absorber, and precisely position the piston 
end face with respect to the metering orifices adjacent the end of the 
stroke so as to provide proper deceleration at the end of the stroke. 
Although the shock absorber manufacturer commonly provids instructions for 
proper installation of the stop members at each installation site, it is 
not unusual that the stop members are not properly positioned with respect 
to the machine tool or transfer arm with the result that the proper end 
limit positions for the transfer arm are not established, or the piston 
bottoms against the end wall of the cylinder with consequent damage to the 
shock absorber, or the end face of the piston ends up in a position within 
the cylinder such that the proper deceleration is not provided at the end 
of the stroke. 
SUMMARY OF THE INVENTION 
The present invention is directed to the provision of a shock absorber 
assembly which includes a stop member which is part of the shock absorber 
assembly and which is readily installed, even by unskilled labor, in a 
precise position to provide ideal stop performance for the shock absorber. 
More specifically, this invention provides a shock absorber assembly which 
includes a stop member which is assembled to the shock absorber at the 
point of installation and which is dimensioned relative to the other 
elements of the shock absorber such that, once installed, it provides 
ideal stop conditions for the shock absorber. 
The invention is specifically directed to shock absorbers of the so-called 
primary type which include a cylinder which has a main body portion and a 
reduced diameter threaded portion at the front end thereof forming an 
annular shoulder with the main body portion and which further includes an 
end wall closing the rear end of the cylinder. 
According to the invention, the shock absorber assembly includes a threaded 
collar which is threaded onto the reduced diameter threaded portion and 
which has a length having a predetermined relationship to the 
predetermined distance between the piston and the end wall of the cylinder 
in the rest position of the piston so that the object against which the 
free end of the piston is impacting moves into limiting contact with the 
leading edge of the collar just before the piston reaches the end wall of 
the cylinder. This arrangement allows a collar to be provided with the 
shock absorber assembly which is precisely manufactured and dimensioned 
relative to the other dimensions of the shock absorber assembly such that 
it may be threaded onto the reduced diameter threaded portion and 
precisely positioned on the reduced diameter threaded portion to provide a 
precisely positioned stop for the absorber. 
In installations where the shock is intended to be rear mounted by the use 
of a further reduced diameter portion at the rear end of the cylinder, the 
stop collar is adapted to be screwed up against the shoulder between the 
main body portion of the cylinder and the front reduced diameter threaded 
portion and has a length that presents the free front annular edge thereof 
at a distance from the free end of the pad on the free end of the piston 
rod that is a major fraction of the predetermined distance between the 
piston and the end of the cylinder in the rest position of the shock 
absorber so that the front annular edge of the collar comes to rest 
against the impacting object just prior to bottoming of the piston against 
the end wall of the cylinder. 
In installations where the shock is intended to be front mounted by passing 
the front reduced diameter threaded portion through a hole in a mounting 
bracket associated with the mounting structure for the shock absorber to 
abut the shoulder between the main body portion of the cylinder and the 
front reduced diameter threaded portion against the rear face of the 
mounting bracket, the collar is adapted to be screwed up against the front 
face of the mounting bracket and has a length that presents the free front 
annular edge thereof at a distance from the free end of the piston rod pad 
that is a major fraction of the predetermined distance between the piston 
and the cylinder end in the rest position at the shock absorber so that 
the front annular edge of the collar comes to rest against the impacting 
object just prior to bottoming of the piston against the end wall of the 
cylinder. 
According to a further feature of the invention, where the shock is 
intended for rear mounting, the shock absorber assembly further includes a 
lock nut sized to screw onto the rear reduced diameter portion of the 
cylinder to facilitate threaded engagement of the free end of the rear 
threaded portion in a threaded bore in a mounting bracket associated with 
the mounting structure for the shock absorber. 
According to a further feature of the invention, the shock absorber further 
includes a mounting flange having a threaded bore for screwing engagement 
over the free end of the rear reduced diameter threaded portion after the 
lock nut has been screwed onto the rear reduced diameter portion. 
According to a further feature of the invention, the shock absorber further 
includes adjustment means adjusting the deceleration forces provided upon 
decelerating impact and the adjusting means includes an adjustment member 
mounted for rotational movement on the cylinder at a location thereon 
remote from the shoulder between the main body portion of the cylinder and 
the front reduced diameter threaded portion. This arrangement ensures that 
the shoulder between the main body portion of the cylinder and the reduced 
diameter front portion of the cylinder will remain fixed irrespective of 
the position of adjustment of the adjustment means so that the shoulder 
provides a fixed reference plane against which the mounting flange or stop 
collar may be abutted to provide proper positioning of the stop collar 
relative to the other elements of the shock absorber installation. 
In the disclosed embodiments of the invention, the collar has a length that 
is sized relative to the length of the reduced diameter threaded portion; 
the rest distance, or stroke, of the piston from the end wall of the 
cylinder; and the rest distance, or effective length, from the impact 
surface of the impact pad to the front end of the reduced diameter 
threaded portion such that an object impacting the pad will engage the 
front annular edge of the collar just prior to the piston bottoming out 
against the end wall of the cylinder. 
In one disclosed embodiment of the invention, intended for use in 
applications where the shock absorber assembly is rear mounted, the collar 
has a length that is slightly greater than the length of the reduced 
diameter threaded portion plus the effective length of the shock absorber 
minus the stroke of the shock absorber so that, with the shock absorber 
rear mounted by the used of a threaded reduced diameter rear portion on 
the cylinder and the collar threaded onto the front reduced diameter 
portion and into abutting engagement with the shoulder defined between the 
main body portion of the cylinder and the front reduced diameter threaded 
portion, the distance from the front annular edge of the collar to the 
front face of the impact pad will be slightly less than the stroke of the 
shock absorber so that the impacting object will engage the front annular 
collar edge just prior to bottoming of the piston against the end wall. 
In another disclosed embodiment of the invention, intended for applications 
where the shock absorber is front mounted by passing the front reduced 
diameter threaded portion through an aperture in a mounting bracket of 
prescribed thickness, the collar has a length that is slightly greater 
than the length of the front reduced diameter portion plus the effective 
length of the shock absorber minus the prescribed thickness of the front 
mounting bracket and minus the stroke of the shock absorber so that, with 
the reduced diameter threaded portion passing through the mounting bracket 
to front mount the shock absorber assembly and the collar threaded onto 
the reduced diameter portion with its rear annular edge abutting the front 
face of the mounting bracket, the distance from the front annular edge of 
the collar to the front face of the impact pad will be slightly less than 
the stroke of the shock absorber so that the impacting object will engage 
the front annular edge just prior to bottoming of the piston against the 
end wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the shock absorber installation as seen in FIG. 1, a machine tool or 
transfer arm 10 is schematically depicted mounted for reciprocal movement 
between left and right positions by a power cylinder 12. At each end of 
its reciprocal movement, a bracket 14 on the member 10 encounters a pad on 
the leading end of the piston rod of a shock absorber 16 so that as the 
member 10 approaches each end of its reciprocal stroking movement, it is 
decelerated to a stop by the respective shock absorber which functions in 
known manner to absorb the kinetic energy of the moving member. In order 
to avoid bottoming of the piston of the shock absorber against the end of 
the cylinder of the shock absorber, precisely define the end limit 
position of the member 10, and precisely position the piston of the shock 
absorber within the cylinder of the shock absorber relative to the 
serially arranged metering orifices within the shock absorber, it is 
customary to install limit stops 18 at each end of the reciprocal movement 
of the member. It is of course imperative that the limit stops 18 be 
precisely positioned relative to the member 10. However, even though the 
shock absorber manufacturer typically includes detailed instructions with 
respect to the installation of the stops 18, it is not uncommon for the 
stops to be improperly or inaccurately positioned with consequent 
bottoming of the piston of the shock against the end wall of the shock, 
inaccurate positioning of the member 10 at either or both of its terminal 
positions, and inaccurate positioning of the piston within the cylinder 
relative to the serially arranged metering orifices. The present invention 
avoids the necessity for installing stops 18 at the shock absorber 
installation by providing stop means as a part of the shock absorber 
assembly. 
The invention shock absorber assembly, including a stop member as a part of 
the shock absorber assembly, is illustrated schematically in FIGS. 2, 3 
and 4 and in detail, in a preferred embodiment, in FIGS. 5 and 6. In each 
case, the invention shock absorber is of the so-called primary type in 
which the external cylinder 20 of the shock absorber includes a main body, 
smooth walled, cylindrical portion 20a; a front reduced diameter threaded 
portion 20b; and a rear reduced diameter threaded portion 20c. Front 
reduced diameter threaded portion 20b forms an annular shoulder 20d with 
main body cylindrical portion 20a and rear reduced diameter threaded 
portion 20c forms an annular shoulder 20e with main body cylindrical 
portion 20a. The shock absorber further includes a piston 22 slideably 
positioned within the cylinder, a piston rod 24 projecting out of the open 
front end of the cylinder, an impact pad 26 carried on the free or front 
end of piston rod 24, and a return coil spring 28 concentrically 
encircling piston rod 24 and extending between pad 26 and a retainer ring 
30 positioned within the open front end of front reduced diameter portion 
20b. The shock absorber assembly further includes an internally threaded 
stop collar 32 threadably mounted on front reduced diameter portion 20b. 
Collar 32 has a length that is sized relative to the length of reduced 
diameter portion 20b, relative to the rest distance, or stroke, of the 
piston 22 from the end wall 20f of the cylinder, and relative to the rest 
distance, or effective length, from the impact surface 26a of the impact 
pad 26 to the front annular edge 20g of reduced diameter threaded portion 
20b such that an object impacting the pad 26, such as the bracket 14 of 
reciprocating member 10, will engage the front annular edge 32a of the 
collar 32 just prior to the piston 22 bottoming out against the cylinder 
end wall 20f. The invention shock absorber assembly is seen in FIG. 2 
applied to a front mount shock absorber installation and in FIGS. 3 and 4 
applied to rear mount shock absorber installations. 
In the front mount shock absorber installation of FIG. 2, front reduced 
diameter portion 20b is passed through a smooth or threaded bore 34a in a 
support bracket 34 and stop collar 32 is threaded onto reduced diameter 
portion 20b to bring the rear annular edge 32b of the collar into abutting 
engagement with the front face of mounting bracket 34. In this front 
mounted installation, the collar 32 has a precise length which is slightly 
greater than the length of reduced diameter portion 20b plus the effective 
length between the front annular edge 20g of reduced diameter portion 20b 
and the front impact face 26a of impact pad 26 minus the thickness "t" of 
mounting bracket 34 and minus the stroke of the shock absorber. When given 
this carefully controlled and precisely defined length, the distance from 
the front annular edge 32a of the collar to the front impact face 26a of 
the pad is slightly less than the stroke of the shock absorber so that the 
impacting object such as bracket 14 will engage the front annular collar 
edge 32a just prior to bottoming of piston 22 against end wall 20f. 
In a typical front mount installation where the effective length of the 
shock absorber is 1.96875 inches, the stroke of the shock absorber is 1.00 
inches, the length of the reduced diameter front threaded portion is 0.90 
inches, the thickness of the mounting bracket is 0.375 inches, and it is 
desired to stop the piston 0.0625 inches shy of end wall 20f, the length 
of collar 32 will be 1.96875 inches minus 1.00 inches plus 0.90 inches 
minus 0.375 inches plus 0.0625 inches or 1.556 inches. 
In the rear mount shock absorber installation of FIG. 3, rear reduced 
diameter portion 20c is passed through a smooth or threaded bore 36a in a 
rear mounting bracket 36 and the stop collar 32 is threaded onto reduced 
diameter front portion 20b until the rear annular 32b of the stop collar 
abuts against shoulder 20d. In this rear mount embodiment, stop collar 32 
has a length that is slightly greater than the length of reduced diameter 
portion 20b plus the effective length of the shock absorber minus the 
stroke of the shock absorber. With this length, the distance from the 
front annular edge 32a of the stop collar to the front face 26a of the 
impact pad is slightly less than the stroke of the shock absorber so that 
impacting objects such as the bracket 14 will engage the front annular 
collar edge 32a just prior to bottoming of piston 22 against end wall 20f. 
For example, if the shock absorber has an effective length of 1.9685 
inches and a stroke of 1.00 inches, the length of reduced diameter portion 
20b is 0.900 inches, and it is desired to stop the piston 0.0625 inches 
shy of end wall 20f, stop collar 32 will have a length equal to 1.9687 
inches plus 0.900 inches minus 1.00 inches plus 0.0625 inches, or 1.9312 
inches. 
The shock absorber assembly of the invention may also, as seen in FIG. 4, 
include a lock nut 38 and a mounting flange 40. When the lock nut 38 and 
mounting flange 40 are included as a part of the assembly, the shock 
absorber is rear mounted by threading the ring 38 onto reduced diameter 
portion 20c and thereafter threading flange 40 onto reduced diameter 
portion 20c into locking engagement with the rear annular face of lock nut 
38. Flange 40 is then secured to a suitable support surface by suitable 
fasteners passing through mounting holes 40a in the mounting bracket. Lock 
nut 38 may also be used in the rear mount arrangement of FIG. 3, in which 
case lock nut 38 is screwed onto rear reduced diameter threaded portion 
20c and into locking engagement with the rear face of mounting bracket 36 
to preclude movement of the bracket relative to the shock absorber 
assembly. 
Since the precise length of the invention stop collar is critical to the 
effective functioning of the invention shock absorber assembly, it is 
important that the stop collar be surface hardened to avoid wear, and 
consequent loss of dimensional integrity, with extended usage. For 
example, the invention stop collar may be suitably heat treated to produce 
a surface hardness of 60 Rockwell on a C scale. 
A specific practical embodiment of the invention shock absorber assembly is 
seen in FIG. 5. The shock absorber assembly of FIG. 5 includes an outer 
cylinder 42 including a main body, smooth walled cylindrical portion 42a; 
a front reduced diameter threaded portion 42b forming a shoulder 42c with 
main body portion 42a; and a rear reduced diameter threaded portion 42d 
forming a shoulder 42e with main body portion 42a. The rear end of outer 
cylinder 42 is closed by an end cap 44 secured to the inner wall of 
cylinder 42 by a retaining ring 46 with an O ring 48 providing a fluid 
seal therebetween. 
A tubular metering cylinder 50 is fixedly supported at its rear end on end 
cap 44 and projects forwardly into cylinder 42. The outer diameter of 
metering cylinder 50 is substantially smaller than the inner diameter of 
outer cylinder 42 so that an annular volume is formed therebetween. The 
forward inner wall of cylinder 50 engages a cylindrical sleeve bearing 52 
adapted to slidingly support an elongated piston rod 54 that projects out 
of the forward end of the assembly. Bearing 52 is held in place by an 
annular bushing 56 fixed relative to outer cylinder 42 by a retainer ring 
58. An O ring 60 provides a fluid seal between bushing 56 and outer 
cylinder 42. An annular seal assembly 62 provides sealing engagement 
between piston rod 54 and the forward inner end of bearing 52 in a known 
manner. 
At its forward end, piston rod 54 carries a button or impact pad 64 secured 
by a screw 66 threaded into a hole in the end of the piston rod. A spiral 
spring 68 extends between the rear side of pad 64 and retaining ring 58, 
thereby acting to return the piston rod to its normal extended position 
after the impacting part is moved away from the shock absorber. A piston 
head 70 is formed integrally with the rear end of piston rod 54. A groove 
on the outer diameter of piston head 70 carries a piston ring 72 bearing 
against the inner diameter of metering cylinder 50. The rear end of piston 
head 70 is formed with a central aperture 74 which communicates at its 
forward end with a central cavity 76. Cavity 76 in turn communicates with 
a vertically oriented bore 78. The concave surface between the larger 
aperture 74 and the smaller cavity 76 acts as a seat for a ball check 
valve 80. A valve retainer is provided rearwardly of the ball by way of a 
retainer ring 82. When the piston moves rearwardly under the influence of 
a force exerted on impact pad 64 by a machine part, the cavity 76 is 
sealed by ball 80 and when the piston moves in the forward direction under 
the force of return spring 54, a free flow path is established through 
aperture 74, cavity 76, and bore 78. 
Bore 78 communicates with an opening 84 in the forward end of metering 
cylinder 50. Opening 84 is in further communication with the annular 
volume 86 between the inner wall of outer cylinder 42 and the outer wall 
of metering cylinder 50. An accumulator pad 88 substantially fills the 
entire volume 86. Pad 88 is formed of cellular rubber which may be filled 
with nitrogen to give it a high degree of resilience and includes an axial 
slot 90 providing clearance for the adjuster mechanism and metering 
orifices as will be explained. 
Four straight-sided circular holes 92, 94, 96, 98 are formed radially 
through the wall of metering cylinder 50. The four holes 92, 94, 96, 98 
are in longitudinal alignment with one another and their respective 
spacings are arranged at exponentially decreasing distances in the 
direction of the rear of metering cylinder 50. 
A metering sleeve 100 slideably surrounds the outer diameter of metering 
cylinder 50. Four internal grooves 102, 104, 106 and 108 are formed on the 
internal periphery of sleeve 100. The grooves are spaced at exponentially 
decreasing distances in the direction of the rear of the sleeve and 
generally correspond to and respectively coact with the four holes 92, 94, 
96, 98 in the metering cylinder. Each groove is of semicircular cross 
sectional configuration and has a diameter slightly greater than the 
diameter of the cylinder holes 92, 94, 96, 98. Grooves 102, 104, 106, 108 
lie in longitudinally spaced parallel planes normal to the axis of the 
cylinder and sleeve and have a uniform semicircular cross section 
throughout their circumferential extent. A straight-sided hole 110 is 
formed in metering sleeve 100 in association with each groove. Each hole 
110 opens at its outer end in the outer surface of sleeve 100 and opens at 
its inner end in the associated groove. Each hole 110 is centered on the 
associated groove and has a diameter slightly less than the diameter of 
the associated groove so that the hole intersects the associated groove at 
a location close to but spaced from the inner periphery of the sleeve. 
Sleeve 100 further includes a relatively large diameter circular hole 112 
positioned between grooves 102 and 104. 
An adjuster mechanism seen generally at 114 is provided to vary the extent 
of overlap between grooves 102, 104, 106, 108 and cylinder holes 92, 94, 
96, 98. Adjuster mechanism 114 includes a stub shaft 116 having an off-set 
cam portion 118 formed at its innermost end. Cam portion 118 is received 
within hole 112 in sleeve 100. Stub shaft 116 is mounted for rotation by 
way of a surrounding collar 120 fixed to outer cylinder 42. A retaining 
ring 122 lies within a circumferential groove in stub shaft 116 above cam 
portion 118 to restrict upward movement of the shaft. An O ring 124 
provides a fluid seal between shaft 116 and collar 120. A socket 126 
formed along the vertical center line of shaft 116 is adapted to receive a 
suitably conforming tool for rotating the shaft. It will be understood 
that rotation of shaft 116 serves to move sleeve 100 in an orbital pattern 
with respect to metering cylinder 50 so that the metering orifice size is 
selectively varied in response to selective rotation of shaft 116 to 
selectively vary the performance and setting of the shock absorber. 
Further details of the manner in which the semicircular grooves coact with 
the metering cylinder to selectively vary the performance of the shock 
absorber are disclosed in Applicant's co-pending U.S. patent application 
Ser. No. 730,334, filed June 7, 1985. 
The shock absorber assembly of FIG. 5 further includes a stop collar 238 
threaded onto reduced diameter threaded portion 42b. As discussed with 
reference to FIGS. 2 and 3, the length of stop collar 128 will vary 
depending upon whether the shock absorber is intended for front mounting 
or rear mounting. Specifically, if, as illustrated in FIG. 5, the shock 
absorber assembly is rear mounted by the use of a mounting flange 130 
engaging reduced diameter threaded portion 42d, the stop collar 238 will 
have a length that is slightly greater than the length of reduced diameter 
outer cylinder portion 42b plus the effective length of the shock absorber 
assembly (that is, the length between the front annular edge 42f of 
threaded portion 42b and the front impact face 64a of impact pad 64) minus 
the stroke of the cylinder. With this arrangement, and as previously 
described, with the collar threaded onto the front reduced diameter 
portion 42b and into abutting engagement with shoulder 42c, the distance 
from the front annular edge 128a of the stop collar to the impact face 64a 
of the impact pad will be slightly less than the stroke of the shock 
absorber assembly so that the impacting object will engage the front 
annular edge 128a of the stop collar just prior to bottoming of the piston 
70 against end wall 44. 
If front mounting of the shock absorber assembly is intended, and as 
previously discussed, the length of stop collar 128 would be slightly 
greater than the length of reduced diameter portion 42b plus the effective 
length of the shock absorber assembly minus the stroke of the shock 
absorber assembly and minus the prescribed thickness of the front mounting 
bracket against which the rear annular edge of the stop collar would abut. 
In actual practice, the shock absorber assembly would come complete with 
instructions with respect to mounting and, specifically, would precisely 
specify the thickness of the front mounting bracket (for example, 3/8 of 
an inch) which would be employed by the installer to ensure precise 
positioning of the front annular edge 128a on the stop collar relative to 
impact surface 64a. 
The invention shock absorber assembly will be seen to provide many 
important advantages. Specifically, the provision of a stop collar that is 
precisely dimensioned with respect to the other critical dimensions of the 
shock absorber assembly avoids bottoming of the piston against the end 
wall of the cylinder with consequent severe damage to the shock absorber 
assembly; provides a proper and precise definition of the end of stroke 
position of the associated transfer arm or machine tool; and precisely 
positions the piston face at the end of its stroke with respect to the 
orifices in the metering cylinder so as to provide precise and proper 
deceleration of the piston as it moves through the critical end portion of 
its stroke. 
Whereas the preferred embodiments of the invention have been illustrated 
and described with reference to the accompanying drawings, it will be 
apparent that various changes may be made in the disclosed embodiments 
without departing from the scope or spirit of the invention.