Note: Descriptions are shown in the official language in which they were submitted.
~037292
APPARATUS FOR OBTAINING RELATIVE ORBITAL
MOVEMENT IN ELECTRICAL DISCHARGE MACHINING
The present invention relates gen~rally to machine tools and
pertains, more specifically, to apparatus for obtaining relative
orbital movement between the tool and the workpiece in electrical
discharge machining.
Present techniques in electrical discharge machining recog-
nize the advantages of providing relative orbital motion between
the workpiece and the electrode employ~d for machining the work-
piece. Prior to the use of such techniques, two or more elec-
trodes were used as machining proceeded from rougher to finer
surface finishes in a complete machining operation. The employ-
ment of relative orbital movement has enabled the use of only a
single electrode for both rough machining and subsequent finer
finishing.
In addition to the above ability to attain rougher and then
finer surface finishes with a single electrode, the availability
of relative orbital movement between the electrods and the work- -
piece enables the machining of a cavity having a configuration
compl~mentary to that of the electrode, but with dimensions en-
larged by an amount determined by the amplitude of the orbital
movement. Well controlled relative orbital motion thus can
achi ve closely controlled tolerances in the manufacture of pre-
cision parts, such as master dies, utilizing electrical discharge
machining.
It is therefore an object of the invention to provide appar-
atus for obtaining closely controlled, accurate orbital movement
of a driven member such that relative orbital motion can be at-
tained between the workpiece and the electrode in electrical dis-
charge machining.
Another object of the invention is to provide apparatus ofthe type described wherein the amplitude of the orbital movement
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037Z92
~$ selectively adjustable for accurate setting of the orbital
displacement, and wherein adjustment may be accomplished while
the apparatus is in operation.
A further object of the invention is to provide a
simplified arrangement of component parts for attaining
selectively adjustable orbital movement of a driven member.
A still further object of the invention is to provide
apparatus as described above which is rugged and will perform as
required, essentially unaffected by the environment present in
electrical discharge machining apparatus.
Still another object of the invention is to provide
apparatus of the type described which economically can be
manufactured from a minimal number of easily fabricated
component parts.
In one aspect briefly as an apparatus for obtaining orbital
movement of a driven member, the apparatus includes a frame, a
first cam mounted for rotation on the frame, the first cam
having a given cam surface and throw and the 1hrow of the first
cam extending in a first direction, and a second cam mounted for
rotation of the frame, the second cam having a given cam surface
and throw and the throw of the second cam extending in a second
direction transverse to the first direction. Drive means are ~-
provided for simultaneously rotating both cams in synchronism.
First coupling means couple the driven member with the first cam
for reciprocating movement along the first direction in response
to rotation of the first cam, the first coupling means
permitting simultaneous reciprocating movement of the driven
member relative to the first cam along the second direction
independent of the ro-tation of the first cam. Second coupling
means couple the driven member with the second cam for
reciprocating movement along the second direction in response to
rotation of the second cam, the second coupling means permitting
simultaneous reciprocating movement of the driven member
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t41ative to the second cam along the first direction independent
of the rotation of the second cam. The given cam surface and
throw of each cam lS such that movement of the driven member
simultaneously along the first and second directions in response
to the synchronized rotation of the cams results in orbital
movement thereof.
The invention will be more fully understood, while further
objects and advantages will become apparent, in the following
detailed description of embodiments of the invention illustrated
in the accompanying drawing, wherein:
FIG. 1 is a plan view of an apparatus constructed in
accordance with the invention, sectioned along line 1 - 1 of
FIG. 4;
FIG. 2 is an elevational view of the apparatus, sectioned
along line 2 - 2 of FIG. 1;
FIG. 3 is a plan view of the apparatus, sectioned along
line 3 - 3 of FIG. 4;
FIG. 4 is an elevational view of the apparatus, sectioned
along line 4 - 4 of FIG. 3;
FIG. 5 is an enlarged, fragmentary plan view illustrating a
segment of a drive shaft of the apparatus;
FIG. 6 is an elevational view of the segment;
FIG. 7 is a cross-sectional view taken along line 7 - 7 of
FIG. 5;
FIG. 8 is a plan view of another apparatus constructed in
accordance with the invention, sectioned along line 8 - 8 of
FIG. ~;
FIG. 9 is an elevational view of the apparatus of FIG. 8,
sectioned along line 9 - 9 of FIG. 8;
FIG. 10 is an elevational view of the apparatus of FIG. 8,
sectioned along line 10 - 10 of FIG. 8; and
FIG. 11 is a fragmentary cross-sectional view taken along
line 11 - 11 of FIG. 10.
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1~37Z92
Referring now to thP drawing, and especially to FIGS. 1
through 4 thereof, an apparatus constructed in accordance with
the invention is illustrated in the form of a work-supporting
table 10. Table 13 has a frame 11, which includes a base 12
and an upstanding side wall 14, and a member in the form of a
platform 16 supported upon the side wall 14. A retaining rim
18 is affixed to the uppermost peripheral edge 20 of the side
wall 14 and includes an upper lip 22 which captures the platform
16 in place upon the side wall 14.
Table 10 is constructed to be placed within an electrical
discharge machine 24 (see FI~. 2), beneath an electrode 26 of
the machine 24. A workpiec~ 28 is affixed to the upper surface
30 of platform 16 to be operated upon by the electrode 26 in an
alectrical discharge machining operation.
As best seen in FIGS. 1 and 2, sufficient clearance is pro-
vided between the platform 16 and retaining rim 18 to permit
lateral movement of platform 16 relative to the side wall 14
and rim 18 in orthogonal directions X and Y. Beneath platform
16, within the confines of side wall 14 and base 12, there is
located a drive mechanism 32 which is coupled to platform 16 by
means which enables the drive mechanism to drive the platform,
which is the driven member, in orbital movemPnt. In this manner,
relative orbital motion is attained between workpiece 28 and
electrode 26.
Drive mechanism 32 includes a drive motor 34 mounted on the
base 12 and carrying a drive sprocket 36. A drive chain 38
drives a sprocket 40 which is affixed to a first drive shaft 42
and the first drive shaft 42 is coupl~d with a second drive
shaft 44 by means of bevel gears 46 such that the drive motor
will rotat~ both drive shafts 42 and 44 in synchronism. The
1037292
longitudinal axes I. and LL of drive shafts 42 and 44, respec-
tively, are orthogonal and each shaft is locat~d precisely, rel
ative to frame 11 and relative to one another, by end bearings
50 and 52 and by V-blocks 54, all carried by the frame 11.
Drive shaft 42 carries a cam 56, while drive shaft 44 in-
cludes two such cams 60. ~ follower in the form of a drive pin
64 lies between cam 56 and a confronting drive surfac~ 66 pro-
vided by a bearing rod 70 carried by a leg 67 of a bracket 68
(see FIG. 4). Brack~t 68 is affixed to platform 16 and leg 67
projects downwardly from the platform toward the drive shaft 42
so as to locate bearing rod 70 at drive pin 64. Resilient m~ans
in the form of a cantilever spring column 72 engag2s l~g 67 of
bracket 68 and bias~s the bearing rod 70 against drive pin 64,
and drive pin 64 against cam 56. The resilient biasing force of
the spring column 72 thus biases the drive shaft 42 into the re-
spective V-blocks 54. Lik~wise, a drive pin 74 li~s between each
cam 60 and a confronting drive surface 76 provided by a b~aring
rod 80 carried by a leg 77 of a bracket 78. Brackets 78 are af- ~
fixed to platform 16 and legs 77 project downwardly from th~ plat- - : :
form toward drive shaft 44 so as to locate a b~aring rod 80 at
each drive pin 74. Resilient means are provided in the form of
cantilever spring columns 82, each spring column 82 engaging a
corresponding brack~t 78 to bias a bearing rod 80 against a cor-
responding drive pin 74 and the drive pin 74 against a corres-
ponding cam 60. In addition, resili~nt means in the form of
spring mechanism 84 maintains a biasing force upon the common end
bearing 52 to maintain tho adjacent ends of th~ drive shafts 42
and 44 in appropriate alignment.
Upon rotation of the drive shafts 42 and d4, by thG opGra-
tion of motor 34, cam 56, the throw of which ~xtends in the X di-
rection, i.e., perpendicular to the longitudinal axis L of drive
1037292
shaft 42, will drive pin 64 and brackPt 68 against the bias force
of spring column 72. In this manner, bracket 68 and, hence, plat-
form 16 will be driven through reciprocating movement along the X
direction. ~t the same time, cams 60, each of which has a throw
extending in the Y direction, i.e., perpendicular to the longi-
tudinal axis LL of drive shaft 44, will drive pins 74 and brack-
ets 78 against the bias force of spring columns 82. Thus, brack-
ets 78 and, hence, platform 16 will be driven through reciprocating
movement along the Y direction. The term "throw" as used herein
denotes the structure of the cam which provides for the movement
imparted by a cam to a corresponding follower and is akin to the
eccentricity of an eccentric. Since the drive surfaces 66 and 76
are parallel to the Y and X directions, respectively, bracket 68
is free to move in the Y direction ralative to the drive pin 64
and cam 56, and brackets 78 and free to move in the X direction
relative to drive pins 74 and cams 60 while the platform 16 is
driven in both the X and Y dirPctions. The combin~d reciprocating
movement of platform 16 simultaneously along the X and Y direc~
tions results in orbital movement of the driven memb~r. Pr~cise ;-~
location and movement of the platform 16 is assured by the three~
point coupling means provided by the three cams, three drive pins
and three bearing rods.
It is readily seen that mounting and precise location of the
drive shafts 42 and 44 is attained by the simple expedients of
V-blocks, end bearings, and the corresponding resilient means,
portions of which also form a part of the means for coupling the ~;
cams 56 and 60 to the platform 16. As best seen in FIGS. 5
through 7, the cams themselves are fabricated readily with the
necPssary precision by forming a cylindrical surface 90 in each
drive shaft, at the drive shaft segment 92 where the cam is
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~037292
located, the cylindrical surface 90 having a central axis C
making an acute angle A with the longitudinal axis L, or LL, of
the drive shaft 42, or 44. All of the cylindrical surfaces 90
can be fabricated with pr~cision by grinding th corresponding
segments 92 of the drive shafts to the same diameter and at the
same angle A. The cylindrical surfaces 90 extend along a finite
length substantially greater than the portions contacted by drive
pins 64 and 74 for purposes which will now be described.
Referring now to FIGS. 1, 3 and 4, as well as to FIGS. 5 to
7, the amplitude of the orbital movement of platform 16 is s lec-
tively adjustable by selectively adjusting the stroke of the re-
ciprocating movement along each of the X and Y directions. To
this end, drive pin 64 is s~lectively movable in a direction par-
allel to axis L (the Y direction) of drive shaft 42, while drive
pins 74 are likewise selectively movable in a direction parallel
to axis LL (the X direction) of drive shaft 44. Since each cam
56 and 60 is comprised of a cylindrical surface 90 having a cen-
tral axis C making an acute angle with the longitudinal axis of
the corresponding drivs shaft, the throw of each cam changes
along the direction of selective movement of the drive pin which
engages the cam. The stroke of the reciprocating movement of the
drive pins, and the corresponding stroke of the hrackets engaged
by the drive pins, is directly related to the throw of the cams.
Thus, selective movement of the drive pins along the cams will
change the stroke of the drive pins and brackets and, hence, the
amplitude of the orbital movement of the platform 16.
In order to accomplish such selective movement of the drive
pins 64 and 74, drive pin 64 is carried by an arm 100 and driv~
pins 74 are carried by arms 102, each of the arms being mounted
upon base 12 for pivotal movement about a separate pivotal axis
P hy means of a mounting block 104. A first link 106 is pinned
~37~92
to arm 100 at 108 while a second link 110 is pinn~d to arms 102
at 112. Both links are pinned to a bellcran~ 114 mounted for
rotation on the base 12 at 116. A rack 118 is affixed to one
snd of link 106 and is engaged by a pinion 120 tsee FIG. 3), af-
fixed to a control shaft 122 which is journalled for rotation in
frame 11 and carries a dial 124 (see FIG. 1). By turning dial
124, links 106 and 110 will be displaced in a direction along
the lengths thereof by equal amounts, thereby moving drive pins -
64 and 74 through equal amounts of displacement and changing the
stroke of the reciprocation of the drive pins accordingly. Lhe ~ -
drive surfaces 66 and 76 provided by bearing rods 70 and 80 ex-
tend in directions parallel to the displacement of drive pins 6
and 74 a distance sufficient to accommodate the displacement of
the drive pins while coupling the platform 16 with the drive
pins. It will be apparent that such adjustment of the amplitude
of the orbital movement of the platform can be accomplished during
operation of the apparatus.
The cylindrical configuration of drive pins 64 and 74 and of
bearing rods 70 and 80 enables only localized contact between the
drive pins and the bearing rods, thus assuring accuracy in accom-
plishing small changes in the stroke of the reciprocation of the
drive pins with concomitant sensitivity and accuracy in changes
in the amplitude of the orbital movement of platform 16.
~ rive mechanism 32 may be sealed-off within the frame 11 to
exclude any deleterious elements in the environment where table
10 is to be used. At the same time, the entire chamber 130 within
which drive mechanism 32 is enclosed can be filled with lubricant
and ~aled. Thus, a seal 132 is provided around the perimeter of
platform 16 to close the chamber 130 established by the base 12,
side wall 14 and platform 16.
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~037Z92
Turning now to FIGS. 8 through 11, another embodiment of the
invention in th~ form of another apparatus constructed in accor-
dance with the invention is illustrated in the form of a work-
supporting table 210. Table 210 has a frame 211, which includes
a base 212 and an upstanding side wall 214, and a member in the
form of a platform 216 supported upon the side wall 214. The
platform 216 is held down against the side wall 214 by magnets
218 which aro affixed to the platform 216 and are attracted to
magnets 220 affixed to frame 211 and juxtaposed with magnets 218.
As best seen in FIGS. 9 and 10, sufficient clearance is pro-
vided between the platform 216 and the sid~ wall 214 to permit
lateral movement of platform 216 relative to the side wall 21~ in
orthogonal directions X and Y. A drive mechanism 232 is coupled
to platform 216 by means which enables the drive mechanism to
drive the platform in orbital movement. Drive mechanism 232
includes a drive motor 234 located externally with respect to
side wall 214. A flexible drive cable 236 is coupled to a drive
shaft 242 such that the drive shaft 2~2 is rotated by drive motor
234. Drive shaft 242 is located precisely, relative to frame 211, .-
by V-blocks 254 carried by the frame, as will be descr~bed in ~ -
greater detail below.
Drive shaft 242 carries a pair of first cams 256, one adja-
cent each end of th~o shaft, and a second cam 260 at the end of
the shaft opposite to the end which is coupled to drive cable
236. A followQr in the form of a drive pin 264 serves as a drive
member and lies between each cam 256 and a confronting drive sur-
face 266 provided by a bearing rod 270 carried by a leg 267 of a
bracket 268 (see. FIG. 10). Brackets 268 ar~ affixed to the plat-
form 216 and each leg 267 projects downwardly from the platform
toward the drive shaft 242 so as to locate a bearing rod 270 at
_g ~
10~7292
~ drive pin 264. Resilient means in the form of a helical
spring 272 extends between the platform 216 and the side wall
214 and biases the platform in a direction which biases the
bearing rods 270 against the eorresponding drive pins 264, and
drive pins 264 against cams 256. The resilient biasing foree of
helical spring 272 also loeates the drive shaft 242 relative to
V-blocks 254, by biasing cylindrical bearing portions 273
carried by cams 256 against the V-surfaces 258 of the V-blocks.
In a similar manner, a drive member in the form of a drive
10 ball 274 lies between cam 260 and a confronting drive surface
276 provided by bearing pad 280 carried by leg 277 of bracket
278. Bearing pad 280 is biased against drive ball 274, and
drive ball 274 is biased against cam 260 by helical spring 272.
In addition, the biasing foree which maintains drive ball 274
against cam 260 serves to locate drive shaft 242 longitudinally
by biasing bearing shoulders 282 carried by eams 256 against
bearing surfaces 259 of V-blocks 254.
Upon rotation of drive 242, by the operation of motor 234,
eams 256, each of which has a throw extending in the X
direction, i.e., perpendicular to the longitudinal axis L of
drive shaft 242, will drive pins 264 and brackets 268 against
the bias force of helical spring 272. In this manner, bracket
268 and, hence, platform 216 will be driven through
reciprocating movement along the X direction. At the same time,
cam 260, which has a throw extending in the Y direetion, i.e.,
parallel to the longitudinal axis L of drive shaft 242, will
drive ball 274 and braekets 278 against the bias force of
helieal spring 272. Thus, braeket 278 and, henee, platform 216
will be driven through reeiproeating movement along the X
30 direetion. Sinee the drive surfaees 266 and 276 are parallel to
the Y and X directions, respectively, brackets 268 are free to
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~03qZ92
move in the Y direction relative to the drive pins 254 and cams256, and bracket 278 is free to move in the X direction relative
to drive ball 274 and cam 260 while the platform is driven in
both the X and Y directions. ~hP combined reciprocating movement
of platform 216 simultaneously along the ~ and Y directions re-
sults in orbital movement of the driven m~mher. Pr~cise location
and movement of the platform 216 is assured by the three-point
coupling means provided by the three cams and th.e rslated coupling
means.
Mounting and precise location of the drive shaft 242 is at-
tained by the simple expedients of V-blocks and corresponding
bearing surfac~s provided on the drive shaft, together with the
resilient means provided by helical spring 272, which also forms
a part of the m~ans for coupling the cams and the platform. The
cams 256 are fabricated readily with the nece.ssary precision by
forming a cylindrical surface 290 on each cam, cylindrical sur-
face 290 having a central axis C. Each cam 256 is then affixed
in place on the drive shaft 242 so that central axis C makes an
acute angle A with the longitudinal axis L of drive shaft 242.
Each cam 256 is provided with the bearing shoulder 282 and an ex-
tension which supplies the cylindrical bearing portions 273. Cam
260 has a flat surface 292 which makes an acute angle B with a
plane PP perpendicular to lonyitudinal axis L of drive shaft 242.
Thus, cam 260 is fabricated readily as a plate and is affixed at
the end of drive shaft 242, in the manner of a swash plate.
The amplitude of the orbital movement of platform 216 is
selectively adjustable by selectively adjusting the stroke of the
reciprocating movement along each of the X and Y directions. To
this end, drive pins 264 are selectively movable in a direction
parallel to axis L (the Y direction) of drive shaft 242, while
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~03729Z
drive ball 274 is selectively movahle in a direction perpendicular
to axis L (the ~ direction), parallel to plane PP. Since cams 256
are comprisecl of a cylindrical surface 290 having a central axis
C making an acute angle A with axis I., and since cam 260 has a
flat surface 292 which makes an acute angle B with plane PP, the
throw of each cam changes along the direction of selective move-
ment of the drive members, in the form of a drive pin or drive
ball, which engage the cam. The stroke of the reciprocating move-
mant of the drive pins and drive ball and the corresponding stroke
of the brackets engaged by th~ drive pins and drive ball, is di-
rectly related to the throw of the cams. Thus, selective movement
of the drive pins and the drive ball along the cams will change
the stroke of the drive pins and the drive ball, and the brackets,
and, hence, the amplitude of the orb.ital movement of the platform
216.
In order to accomplish such selective movement of the drive
pins 264 and drive ball 274, drive pins 264 are each carried by an ;
arm 300 and drive ball 274 is carried by an arm 302. ~rms 300 are
flexible in the X direction, but not in the Y direction and are
affixed to a first slide 304 which is mounted for sliding movement
relative to frame 211 parallel to the longitudinal axis L (in the
Y direction) by means of guide blocks 306 and 308 fixed to base.
212. Likewis~, arm 302 which is flexible in the Y direction, but
not in the X dir~ction, is affixed to a second slide 310 which is
mount~d for sliding movement relative to frame 211 perpendicular
to the longitudinal axis L (in the X direction) by means of a guide
block 312 fixed to base 212. A first rack 314 carried by first
slide 3Q4 is engaged by a pinion 316 carried by a control shaft
318 journaled for rotation in frame 211. A control dial 320 is
carried by control shaft 318 outside the side wall 214 and is jux-
taposed with a pointer 322 and a clamp 324. IJpon release of clamp
1~37292
324, dial 320 may be rotated to rotate control shaft 31~ and pin
ion 316 to move first slide 304 in the Y direction, together with
drive pins 264. Simultançously, a s~cond rack 32~, also carried
by slide 304, will move in th~, Y direction, rotating another pin--
ion 328 which engages a rack 33n on second slide 310 to move
slide 310 in the X direction, togeth~r with driv~. ball 274. Thus,
by turning dial 320, slides 304 and 310 each will be displaced in
a direction along the length thereof by equal amounts, thereby
moving driv~ pins 264 and drive ball 274 through equal amounts of
displacement and changing the stroke of the reciprocation of the
drive pins and drive ball accordingly. ~he drive surfaces 266
and 276 provided by bearing rods 270 and bearing pad 280 extend
in directions parallel to the displacement of drive pins 264 and
drive ball 274 a distance sufficient to accommodate the displace- ''
ment of the drive pins and drive bal.l while coupling the platform
216 with the drive pins and drive ball. Once the appropriate ad-
justment of the amplitude of the orbital movement of the platform
is made, clamp 324 may be closed to fix the position of dial 320
and slides 304 and 310. Adjustment can be made during operation
of the apparatus.
It is to be understood that the above detailed description of
embodiments of the invention are provided by way of example only.
Various details of design and construction may be modified with-
out departing from the true spirit and scope of the invention as
set forth in the appended claims.
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