Linear motion impactor device

A linear motion impactor device includes an impactor (28) which provides force to a hammer shank (56) only upon application of the hammer against a surface to be impacted thereby saving power and reducing noise during periods of non-use. The impactor (28) which operates on the hammer shank (56) is mounted in a housing (12) and is formed with a bore (30) normally coincident with the axis of rotation (22) of an eccentric cam (24) which is rotated by a power source (20). The impactor (28) is retained in this center-line position by a compression pad (38) positioned between the impactor (28) and the housing (12) and further positioned diametrically opposite the hammer shank (56). In the two embodiments described, either linear bearings (76, 78) or shear pads (42, 44) ensure linear motion to the impactor (28) during operation.

TECHNICAL FIELD 
This invention relates to an impactor device. In particular, it relates to 
an impactor device which may be used in combination with rock breakers, 
crushers, pile drivers, compactors or the like. Specifically, the device 
provides high energy, for example, to break rock or the like. 
BACKGROUND ART 
In earlier impact tools such as that described in U.S. Pat. No. 3,770,322, 
issued to Cobb et al. on Nov. 6, 1973 and also in U.S. Pat. No. 3,922,017, 
issued to Cobb on Nov. 25, 1975, the reciprocated hammer is driven by an 
eccentric cam to which the impactor is journaled. In the manner described 
in these patents, energy is constantly utilized to reciprocate the hammer 
under load or no load conditions. As a result, power requirements are 
higher than necessary. Additionally, ambient noise from the impacting 
device is constant under load or no load conditions. 
Eccentric impactors of the type described in the above patents generally 
provide non-linear motion to the impactor. Although the non-linear motion 
may be converted to linear motion at the hammer by various schemes, some 
energy is lost during the conversion process. Commonly, it has been found 
that a ball and socket type joint, similar to that described in U.S. Pat. 
No. 3,922,017, is satisfactory to convert the non-linear motion of the 
eccentric to linear motion at the hammer. Other schemes could include a 
pivoted arm arrangement or the like, such as disclosed in U.S. Pat. No. 
3,770,322. In both these earlier schemes, a thrust bearing is required 
between the eccentric cam and the impactor portion of the device. 
In eccentric driven impactor devices of the type described herein, it is 
usually necessary to seal the rotating eccentric or driving mechanism from 
the environment in which it operates. This is necessary because of the 
generally highly abrasive nature of the material being broken. This 
material usually is rock of some form or another and would certainly have 
detrimental effects on bearings and attendant components in the drive 
mechanism. Because of the reciprocating nature of the impactor operating 
on the hammer, a flexible seal is necessary between the drive chamber and 
the hammer. Fatigue in the flexible seal becomes a real problem and must 
be guarded against by both the manufacturer and the user. It is well known 
that fatigue in any member may be measured by the number of flexures of 
that member. 
It is elementary that useful life may be lengthened by either increasing 
the available number of flexures in the material or decreasing the 
absolute number of flexures of the material. Materials suitable for 
flexible seals of the type envisioned herein are well developed and it is 
unlikely that a substantial increase in the mean time before failure will 
occur in such seals in the immediate future. Accordingly, the manufacturer 
of impacting devices is desirous of decreasing the number of flexures, 
particularly unnecessary flexures which occur during repositioning of the 
impactor device, notwithstanding efforts of the operator to shut-down the 
machine during such times. Further, it is appropriate to limit the degree 
of flexure by limiting deflection of the impactor to that necessary to 
accomplish the job. 
In some conventional devices, the throw of the impactor is constant 
irregardless of the work to be accomplished. Control of the force applied 
to the hammer by the constantly reciprocating impactor is usually 
accomplished by positioning the hammer at varying distances from the 
impactor. Therefore, if a relatively light breaking force is appropriate, 
the hammer or other work member is positioned relatively further away from 
the impactor so that impact on the hammer for delivery to the workpiece is 
present only at the extreme throw of the eccentric. Nevertheless, full 
flexure of the case seal occurs on each blow of the impactor. 
In another type of impactor drive mechanism, such as disclosed in U.S. Pat. 
No. 3,868,145, granted to Cobb et al. on Feb. 25, 1976, the impact member 
is an annular ring journaled on an eccentric shaft, so that the impact 
member contacts the hammer upon the orbital rotation of the ring on an 
eccentric shaft. In this particular type of drive mechanism, the impact 
ring is rotated either in a regular or an irregular pattern to prevent 
flattening of the faces of the impactor ring, thus necessitating a 
replacement or change. Rotation is accomplished in several ways, such as 
providing conical washers which rotate the impactor ring. Nevertheless, 
the resulting pattern formed by the ring upon rotation is non-linear. 
Thus, at the point of contact of the impact ring with the hammer, a 
"wiping" action may occur across the face of the hammer, resulting in 
unnecessary wear on the hammer and the impactor. 
DISCLOSURE OF THE INVENTION 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
In one aspect of the present invention, an impact device compresses a shaft 
mounted for rotation in a mounting. The shaft defines an axis of rotation 
and has an eccentric portion defining a predetermined throw diameter. An 
impactor defines a bore having a diameter at least equal to the 
predetermined throw diameter of the eccentric portion of the shaft and is 
mountable in the mounting about the eccentric portion of the shaft so that 
the eccentric is free to rotate therein. 
The present invention overcomes loss of power inherent in conventional 
eccentric driven impact devices while providing linear motion to the 
impactor. This linear motion eliminates "wiping" or "rolling" across the 
face of the hammer shank and further can lessen deflection of a case seal 
mounted about the impactor shank. The impactor, because of its bore having 
a diameter at least equal to the throw diameter of the eccentric portion 
of the shaft, is passive until an exterior load applied to the hammer 
laterally displaces the impactor in the mounting so that the impactor may 
then operate on the hammer with a counterforce.

BEST MODE FOR CARRYING OUT THE INVENTION 
Reference is made to FIG. 1 wherein an impact device 10 is depicted partly 
in section. Impact device 10 is comprised of a mounting or housing 12 in 
which a shaft 14 is journaled by appropriate means, such as a first 
bearing 16 and a second bearing 18, as shown schematically in FIG. 2. 
Shaft 14 is rotated by appropriate means, such as a motor 20. Motor 20 may 
be powered by a hydraulic source or the like. Shaft 14 defines an axis of 
rotation 22. 
Shaft 14 has affixed thereto by appropriate means well known in the art a 
cylindrical eccentric cam 24 which may be balanced by one or more 
counterweights 26, also mounted for rotation with shaft 14 in a manner 
well known in the art. Eccentric cam 24, when rotated by shaft 14, 
generates a circle having a radius R and a center coincident with the axis 
of rotation 22. This circle is hereinafter referred to as the throw 
diameter of eccentric cam 24. 
Resiliently mounted in housing 12 about eccentric cam 24 is an impactor 28. 
Impactor 28 is generally in the form of an annular ring having an opening 
or bore defined therein by a cylindrical surface 30. The diameter of 
surface 30 is equal to at least twice the throw radius R of eccentric cam 
24 and such diameter is preferably greater (1.2 to 1.5 times) than the 
outside diameter of cam 24. It should be understood that cam 24 could 
assume other shapes (e.g. elliptical, irregular) in accordance with well 
known design principles. 
Impactor 28 has formed therewith an extension 32 which extends outwardly of 
housing 12 through a neck 34. Extension 32 is mounted in neck 34 by an 
elastomeric case seal 36. Affixed to housing 12 at a point generally 
displaced 180.degree. circumferentially from neck 34 of impactor 28 is an 
elastomeric compression pad 38 which contacts the outer surface 40 of 
impactor 28. Athough an elastomeric pad is shown, other shock absorbing 
means such as springs would suffice to resiliently bias impactor 28 so 
that the bore defined by cylindrical surface 30 is coaxial with axis of 
rotation 22. 
Referring specifically to FIG. 1, diametrically opposed shear pads 42 and 
44 are also composed of an elastomeric material and are mounted between 
housing 12 and the outer surface 40 of impactor 28 substantially midway 
between compression pad 38 and extension 32 and on opposite sides of 
impactor 28. The compression pad 38 and the shear pads 42 and 44 may be 
each affixed to the housing 12 by a plate, such as a plate 46 bonded to 
the respective pad, and a threaded hole 48 or the like in which a bolt 50 
may be engaged to affix the compression pad 38 or the shear pad such as 
shear pad 42 to the housing 12. A similar structure may be seen in FIG. 1 
affixing shear pad 44 and compression pad 38 to housing 12. 
Case seal 36 and compression pad 38 cooperate to retain impactor 28 
centered on the axis of the throw diameter of eccentric cam 24, in the 
direction of arrows T in FIG. 1. Shear pads 42 and 44 maintain the 
linearity in the motion of impactor 28 when it is displaced by a force 
acting on a hammer shank 56. 
Referring now to FIG. 2, it can be seen that a passage 52 extends radially 
from an axial bore 54 formed in eccentric cam 24. Axial bore 54 is 
connected with the source of lubricating fluid (not shown) so that 
lubricating fluid may be passed under pressure to axial bore 54 and 
passage 52 to impinge upon inside surface 30 of impactor 28. The point of 
contact of lubricant should be less than 90.degree. in advance of the 
point 57, the point of closest approach of eccentric cam 24 to inner 
surface 30 of impactor 28. Thus, oil or other lubricating fluid 
communicated through passage 52 lubricates the inside cylindrical surface 
30 of impactor 28 to reduce wear as the point 57 rotates about inside 
surface 30 of impactor 28. 
INDUSTRIAL APPLICABILITY 
It is envisioned that the impact device embodying this invention may be 
utilized, for example, in a rock breaker such as described in U.S. Pat. 
No. 3,868,145. In particular, impactor 28 may be utilized to operate on a 
shank 56 of a hammer (not shown) which, in turn, may operate on rocks or 
other such materials. Shank 56 may be constrained for reciprocation 
between minimum and maximum throws by a portion of housing 12 or the like 
in a manner well known in the art. Illustrative of this is a tang 58 which 
may extend outwardly of shank 56 for reciprocation between bifurcated legs 
60 and 62 of housing 12. A force applied to shank 56 to move the shank 
toward impactor 28 will cause the shank to contact impactor 28. 
As a force applied to shank 56 increases, impactor 28 will move downwardly 
in FIG. 1 compressing compression pad 38 so that a point 64 on inside 
surface 30 of impactor 28 is located inside the throw radius of eccentric 
cam 24. As eccentric cam 24 rotates, the point 57 on the surface of 
eccentric cam 24, representing major radius R of the cam, will act on the 
inside surface 30 of impactor 28, thus forcing impactor 28 upwardly as 
indicated in FIG. 1 to act on shank 56 and, in turn, the hammer (not 
shown) of the rock breaker in which this particular device is envisioned 
as being used. 
Concurrently, lubricating fluid (oil) is supplied through passages 54 and 
52 to impinge on inside surface 30. This constant flow of lubricant 
provides an oil film at all times between the contacting metal surfaces to 
retard wear thereof. It should be noted that the condition shown in FIG. 1 
is the steady state, that is, without a force imposed on shank 56. It can 
be seen that impactor 28 is held in a position so that the center of the 
circle formed by inside surface 30 is substantially coincident with the 
axis of rotation 22 of eccentric cam 24. Thus, in the normal steady state 
condition, no impact force is applied to shank 56, nor will any impact 
force be applied to shank 56 until an opposite force is applied thereto. 
The result of this invention is a substantial savings in power in the 
impactor device in that no power is expended on shank 56 until the actual 
work begins. Thus, power expended during the steady state and no impact 
condition illustrated in FIG. 1 is only sufficient to rotate eccentric cam 
52 and a counterweight 26. Rotation of these devices is appropriate during 
the steady state operation in order to maintain the inertia of the device. 
During operation, the shear pads 42 and 44 act on the impactor 28 so that 
motion of the impactor 28 is substantially linear. In prior art devices, 
since the inside surface, corresponding to surface 30, of the impactor was 
coincident with and journaled on the cam surface corresponding to surface 
66 by a thrust bearing, the resulting motion of the impactor was 
non-linear. The linear motion provided by the present device reduces wear 
on the case seal 36 and further reduces wear on the bearing surfaces 
between shank 56 and impactor 28 by eliminating the wiping action found in 
the conventional impactor device. Furthermore, no thrust bearing is 
necessary between the impactor 28 and the eccentric cam 24. 
AN ALTERNATE MODE FOR CARRYING OUT THE INVENTION 
Referring to FIGS. 3 and 4, an alternate mode or embodiment is shown for 
carrying out this invention. In this alternate mode, like parts are 
indicated by the same numerals as used in the primary embodiment with the 
addition of a prime symbol ('). In FIG. 3, an impactor 70 is formed with 
two parallel sides or faces 72 and 74 which are aligned substantially with 
the axis of reciprocation of the impactor. Faces 72 and 74 are formed to 
bear against parallel sides or linear bearings 76 and 78 which are affixed 
to a housing 12' by appropriate fastening means, such as bolts 80. 
As in the first described embodiment, a compression pad 38' and a case seal 
36' cooperate to retain the impactor 70 in a position so that an eccentric 
cam 24' may rotate freely with an inner cylindrical surface 30' of 
impactor 70. Once impactor 70 is moved downwardly as indicated in FIG. 3, 
the eccentric cam 24' will act against the inner surface 30' to impart 
reciprocal motion to impactor 70 and thus shank 56' as in the embodiment 
of FIGS. 1 and 2. 
INDUSTRIAL APPLICABILITY OF THE ALTERNATE EMBODIMENT 
The industrial applicability of the alternate embodiment of FIGS. 3 and 4 
corresponds to that of the FIGS. 1 and 2 embodiment. Specifically, this 
impact device may be used on a rock breaker type machine and overcome 
power losses and provide the other operational desiderata discussed above 
in comparison to prior art devices of similar application. 
In both embodiments, it should be apparent to those skilled in the art that 
the tool which has been described as being associated with shank 56(56') 
could be affixed directly to impactor 28(70). 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and appended claims.