Indexing apparatus for electron beam drilling

In an apparatus for manipulating workpieces in an electron beam drilling machine, workpieces are mounted on rotatable disks which in turn are mounted on a housing which is rotatable and translatable. Each disk, as a fixture holding the workpiece, is unlocked, rotated, and locked in a new position by the motion of a single driving member and associated elements. The single driving members associated with each workpiece indexing assembly are driven through a system of gears from a single central shaft which passes through the vacuum chamber wall to externally mounted actuators and controls.

BACKGROUND ART 
1. The present invention relates to the field of indexing mechanisms, most 
particularly those adapted for use with welding and drilling processes 
using beam energy, such as that provided by electron beams. 
2. There are a great number of indexing mechanisms which are revealed by 
the prior art. Indexing mechanisms, as the name denotes, have as their 
function the sequential positioning of parts with respect to some fixed 
point. However, special problems arise when indexing is required to be 
undertaken in the harsh environment of an electron beam chamber. Not only 
does the presence of a high vacuum complicate the design, but the 
apparatus must be tolerable of the heat and shower of molten metal 
particles which are generated during the drilling process. 
When specifically applied to the drilling of small diameter holes in the 
surface of a superalloy airfoil, the complexity of manipulation is 
increased. One reason for this is in the asymmetric nature of a gas 
turbine airfoil. Characteristically, the desired holes are oblique to the 
surface, which is often highly contoured in three dimensions. For 
practical purposes, in most electron beam drilling machines, the beam path 
is fixed within a small angle. Therefore, to put a row of holes in an 
airfoil, the part must be translated along the length of the row. To 
produce more than a single row on an airfoil, means must be further 
provided to translate the airfoil laterally with respect to the row 
length. To change the angle of any particular hole or part of a row, the 
part must be rotated with respect to the beam axis. If a multiplicity of 
airfoils are placed in a welding chamber at the same time, then further 
means must be provided for presenting each of the airfoils to the beam 
path. Thus, when a multiplicity of parts is sought to be simultaneously 
drilled with complex hole patterns, the cumulation of mechanical movements 
which are necessary can lead to systems which are unduly complex and 
therefore unreliable. 
A further demand of electron beam hole drilling in airfoils is the accuracy 
which is desired. For example, a typical airfoil may require that holes of 
0.45 to 1 mm diameter be spaced apart a distance of about 1.753.+-.0.254 
mm, with the hole axes being aligned with better than 0.1 degree of the 
desired positions. 
As might be expected, there are a great number of known devices for 
indexing parts in rotary manner. U.S. Pat. No. 3,532,009, Hogan et al., 
shows a typical apparatus where rotational motion to the nominal position 
is accomplished by an indexing pawl, and thereafter a final, exact 
position is accomplished by a second independently operated positioning 
plunger. U.S. Pat. No. 2,985,038, Tandler et al., shows a relatively 
complex peg and pawl positioning system. Mead, in U.S. Pat No. 2,968,973, 
shows a chain-motivated rotary table where the nominal position is 
achieved by means of a spring-loaded pin; the pin is disengageable by 
means of a linkage activated by the same prime mover piston as activates 
the chain. As reference to the foregoing patents will indicate, the prior 
art mechanisms for rotational indexing are comprised of a great number of 
elements. For use in a vacuum chamber necessary for electron beam 
drilling, it is desirable that the number of elements be reduced, that the 
number of actuators or actuator rods be reduced, and that the prime movers 
be located external to the chamber. 
DISCLOSURE OF INVENTION 
An object of the invention is to provide a simple and reliable apparatus 
for manipulating and indexing a multiplicity of workpieces within a vacuum 
chamber. 
According to the invention a multiplicity of assemblies is mounted on a 
translatable and rotatable housing which is insertable into a vacuum 
chamber. Each assembly contains a rotatable disk for holding an airfoil. 
Means are provided for rotating or indexing the disks with respect to the 
housing, to positions which correspond with the rows of holes which are 
sought on the airfoils. Means are further provided for locking the disks 
in precise position. 
In each assembly, a single driving member actuates rotation and locking of 
the disks. In the preferred embodiment the single driving member is a rack 
gear shaft capable of simple linear motion. Each assembly has a rack gear 
shaft driven by a spur gear. The spur gears at all assemblies are driven 
by a central gear mounted on a single shaft which extends through the 
vacuum chamber wall. 
The motion of the central gear and multiple rack gear shafts not only 
causes rotary motion of the disks but also causes engagement and 
disengagement of a shot pin which precisely locates the disk. This is 
embodied by each disk having both teeth and precision dimension cavities 
on its periphery. The number of teeth and cavities corresponds with the 
number of rows of holes to be drilled in the workpiece. Each rack gear 
shaft is mounted on the housing in proximity to each disk. Through a 
linkage, each rack gear shaft is connected to a tapered shot pin which 
selectably engages with the holes on the periphery of each disk. When a 
rack gear shaft is moved, the shot pin is caused to withdraw from a disk, 
thereby unlocking it from its position. Further translation of a rack gear 
shaft causes a spring loaded pawl mounted theron to engage with one of the 
teeth on the periphery of a disk, thereby causing the disk to rotate to a 
new nominal index position. The rotation of each spur gear is then 
reversed by action of the central gear with which they are all engaged. 
This causes every rack gear shaft to reverse direction. Each pawl 
disengages from each disk and the rack gear shaft and pawl combinations 
are returned to their original positions without further interaction with 
the disks. The reverse motion of the rack gear shafts also causes the shot 
pins to engage the proximate cavities on the disk peripheries. The shot 
pins are tapered. Thus a shot pin, on entering a cavity, will bring a disk 
to an accurate and final position, where it is locked by continuation of 
engagement of the shot pin. Thus, all stations are simultaneously 
unlocked, rotated to a nominal new position, precisely positioned and 
re-locked. This action is all caused by the simple rotation, first in one 
direction and then in the opposite direction, of the shaft on which the 
central gear is mounted. Rotation of the shaft may be undertaken by 
various means; the preferred means is a rotary vane air cylinder and 
attendant control system. 
To drill several rows of holes in a part, the airfoils are identically 
mounted on disks which are all initially set at their zero position. Then 
a row of holes in each airfoil is produced by programmably rotating and 
translating the main housing. Next, rotation of the housing is ceased and 
the above-described indexing system is used to place the airfoils in a 
second position. Drilling of the second row then takes place by rotation 
and translation of the housing, in a manner analogous to that employed to 
drill the first row. Further rows may be made in like manner. 
Particular features of the invention are that only mechanical elements are 
present within the vacuum chamber, and the system is therefore highly 
reliable. Further, since there is but a single actuating shaft passing 
through the wall of the chamber, preservation of the vacuum integrity of 
the system is greatly simplified. 
The foregoing and other objects, features and advantages of the present 
invention will become more apparent from the following description of 
preferred embodiments and accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The invention is described in terms of the drilling of holes in airfoil 
workpieces using an electron beam, but it will be seen that the invention 
will be useful in other manufacturing operations where precise indexing 
and positioning are desired. As FIG. 3 illustrates, the invention is 
described in the context of drilling a series of precisely located small 
holes 19 along the length of an airfoil 21 in a manner well-known to 
provide for film cooling. For illustration, three rows of holes are 
drilled in five parts. The invention will be applicable to other 
quantities of hole rows and parts. 
With reference to FIG. 1, to perform electron beam drilling, parts are 
inserted into a vacuum chamber 40 having an electron beam gun apparatus 42 
mounted thereon. While the angle at which the beam approaches the 
workpiece may be varied somewhat by manipulation of the beam path, the 
primary means of obtaining holes at a particular position and angle on a 
surface of a workpiece is to appropriately position and tilt the workpiece 
directly under the beam. It is desirable to have as many workpieces as 
possible inserted into the chamber prior to the initiation of a drilling 
sequence, to speed production by avoiding repetitive evacuation times. The 
airfoil parts 44 are mounted off a base plate 54 at the end of the primary 
manipulator shaft 46 which enters the chamber through a rotary and sliding 
seal plate 48 and has connected to it driving means 50 and 52, located 
external to the chamber. The shaft 46 is mounted in a frame 49 and is 
capable of motion through linear driver 52 and rotary driver 50. When the 
parts are fixed with respect to base plate 54, a hole in each part is 
obtainable by rotating the plate 54 by driver 50 to position each part in 
sequence under the beam; thereafter, a row is obtainable by longitudinally 
translating base plate 54 and parts thereon along the length of the row 
while repeating the drilling in each part, as for the first hole. In the 
most convenient practice, the rows are progressively drilled in all parts 
by continuous rotation of the main plate and timed beam pulsing in 
coordination therewith. It will be seen from FIGS. 2 and 4 that when the 
airfoils 44 are mounted fixedly at the end of the shaft 46 on base plate 
54, only certain surfaces may be presented to the beam path 56 by the 
foregoing motions. Previously, after a single row was drilled in a group 
of parts, the vacuum would be broken and the parts were then manually 
rotated with respect to the base plate 54; then the group was reinserted 
into the chamber to drill a new row. Thus, an object of the present 
invention is to provide better means for rapidly and accurately rotating 
the parts 44 with respect to the base plate 54 without removal from the 
vacuum. The mechanisms which accomplish this are comprised generally of 
the apparatus mounted on the base plate 54 denoted in FIG. 8 generally by 
the dashed line 58 together with the mechanisms contained within the 
dashed line 60, mounted on the opposing exterior end of the main shaft. 
The mechanisms 60 primarily constitute the actuators and controls which 
cause motion within the chamber of the apparatus which grip the parts. 
FIG. 2 shows a fragmentary end view of the apparatus 58 which is located 
inside the chamber. Elements of this apparatus are also shown in cross 
section in other Figures which may be referred to. A housing 62 is 
attached to the base plate 54. Mounted on shafts 88 at equally spaced 
increments around a circumference of the housing 62 are five rotatable 
disks 64. A gear, pawl and shot pin mechanism described in more detail 
below, both causes rotational motion of each of the disks and accurately 
locks them in position. 
The disk 64, shown in more detail in FIG. 3 has a series of cavities 20 and 
teeth 16 on its exterior, the number of each at least equal to the number 
of rows to be drilled. The disk 64 is adapted to receive a fixture 68 
which in turn is suited to accurately hold a part 44, 21. The circular 
shape of disk 64 is somewhat arbitrary, other than the portion which has 
the teeth and cavities, as will be evident from the following discussion. 
Thus, it is seen that rotation of the disks 64 will present a new portion 
of the surface of each airfoil 44 to the beam, as in turn each airfoil is 
presented for drilling by rotation of the base plate 54. Consequently, it 
is necessary that the rotation of all the disks 64 be accurately 
controlled, from one index position to another. The rotational indexing 
mechanism is now described. 
FIG. 4 is an end view of one of the five indexing assemblies mounted on the 
housing 62. FIGS. 5-7 show fragmentary cross sections of the indexing 
mechanisms and should be also now referred to. The airfoil, not shown in 
FIG. 4, is mounted on the disk 64 which pivots about shaft 88. Rotational 
motion of the disk is obtained by engagement of a spring biased pawl 14 
with teeth 16 which protrude from the rim of the disk. Once the disk is 
shifted to a new position by action of the pawl, it is very accurately 
located by engagement of a sliding shot pin 18 with one of the cavities 20 
also located on the periphery of the disk, but at a different plane than 
the aforementioned teeth 16, as is evident from FIGS. 3 and 5. 
The pawl 14 is mounted on a slidable rack gear shaft 22 which is contained 
in bushing 24 mounfted on the housing 62. The shat 22 has a rack gear 
portion 26 which engages a gear 66, 28 fixed to shaft 68 that is rotatable 
in the housing. Thus rotation of the gear 66, 28 will cause the rack gear 
shaft 22 to translate. 
The rack gear shaft 22 is also connected to the extension of the shot pin 
18 by means of a link 30 which is pivotally mounted at each end. The rack 
gear shaft and the shot pin are mounted at 90.degree. angles while the 
link is mounted at nominally a 45.degree. angle to the shot pin and rack 
gear shaft. The shot pin 18 is slidably mounted in a bushing 32 which is 
fixed to the housing 62. The dimensions of the three interconnected 
elements (18, 30, and 22) are such that, upon initial sliding motion of 
the rack gear shaft and motion of the pawl in the direction of the disk 
64, the shot pin 18 is caused to retract from the hole 20, 90 in the disk. 
As the shot pin is retracted fully from the hole, the motion of the rack 
gear shaft continues until the pawl engages a tooth 16, 94 and thereby 
causes rotary motion of the disk. When the desired angular degree of 
rotation is attained the motion of the rack gear shaft is reversed. 
Whereupon the shot pin is caused, by virtue of the linkage motion, to 
advance toward the disk and thereafter to enter the hole 20, 92 which has 
been newly positioned on the axis of its path. The shot pin has a taper at 
its nose 34 an thus causes any slight further movement of the rotary table 
necessary to bring the principal diameter of the shot pin and the hole 
into alignment. Since the shot pin closely fits the hole in the disk, and 
since the shot pin is accurately and firmly fixed to the housing upon 
which the disk is mounted as well, the accurate desired re-positionable of 
the airfoil is obtained. Thus it is seen the slidable rack gear shaft is a 
single driving member which both causes rotation and locking. 
The pawl 14 is spring biased (not shown) toward the disk teeth, to engage 
them. Travel in the absence of proximity to a tooth is limited by pin stop 
95. Thus, during the just-described reversing motion of the rack gear 
shaft 22, the pawl rides up over any teeth 16 in its reverse path and 
thereafter resumes its original position, ready for the next indexing. Of 
course, modifications in the pawl-teeth configuration may be made within 
the scope of the invention. Overshoot of the disk during forward rotation, 
or reverse motion due to pawl friction is prevented by a ball spring 
plunger mounted on the housing which engages a series of detents on the 
disk corresponding with the disk cavities. These elements are not shown. 
Other frictional means may be used to proximately stabilize the disk in 
its position. 
In the preferred embodiment, rotation of the disks 64 is controlled by the 
gears 66. The manner in which the motion of a gear 66 is obtained will now 
be treated. Referring to FIG. 8, in which one of the five similar gear 
sub-assemblies in housing 62 is shown, gear 66 is mounted on a rotatable 
shaft 68 which has at its opposing end spur gear 70. The spur gear 70 
engages a central gear 72 which is fixedly mounted to an inner drive shaft 
74 which is rotatable within the housing 62, main plate 54, and bellow 
manipulator shaft 46. Seal 96 preserves the vacuum in the chamber. Thus, 
it may be seen that if the housing 62 is rotationally fixed, rotation of 
the single main drive element, shaft 74, both clockwise and 
counter-clockwise, will cause corresponding rotation of the gears 66, and 
consequent indexing of all the five airfoil holding disks simultaneously. 
The necessary motion of the drive shaft 74 is achieved by means of a rotary 
vane type air cylinder 76, as shown in FIG. 9. Air supplied by a four-way 
flow valve 82, in response to a signal from the control system 84, causes 
90.degree. rotation of the cylinder output shaft 80 which is coupled to 
the drive shaft 74. Mechanical stops (not shown) limit the rotational 
motion of the shaft 80 with precision. The rotational motion of the drive 
shaft at its end points is confirmed by magnetically activated switches 
86, according to the magnetic field produced by magnet 86' which is 
fixedly attached to the shaft 80. Signals from the magnetic switches 
activate the control system for the next step. When indexing is partially 
accomplished, the next step is reverse rotation of the inner shaft to 
complete indexing by shot pin insertion. When indexing has been fully 
completed, the next step is motion of manipulator 46 or initiation of beam 
drilling. 
As pointed out, the manipulator shaft 46 rotates and translates in space, 
and the rotary motion of inner shaft 74 is with respect to the manipulator 
shaft. Thus, the actuator cylinder 76 and desirably the sensor system 86, 
86' move with the shaft. The controls (82, 84) may move with the shaft or 
be connected to in with suitable connectors. It should be apparent that 
other means of effecting the desired rotation of the shaft 74 may be 
employed. 
It should be seen that the exact degree of rotation of shaft 74 and the 
separate but simultaneous movements of the gears 66 is not highly 
critical. The disk 64 need only be caused to assume a new position with 
accuracy sufficient to present a new hole 20 for engagement by the 
tapered, smaller diameter end of the shot pin 18. Then, when the shot pin 
advances into the hole and engages it with its maximum diameter, any 
mis-positioning will be corrected and a location obtained consistent with 
the close tolerance characteristics of shot pins and locating holes 
(.about.0.025 mm). The final linear resting position of the shot pin 
mechanism is not critical, once the major shot pin diameter intercepts the 
hole. In practice it is found that angular location of parts on a 10 cm 
diameter housing may be obtained to a tolerance .+-.0.02 degrees. The 
apparatus consequently avoids any costs or problems which would result 
from the need for highly accurate gear positioning, anti-backlash 
mechanism, feedback loops, and the like. At the same time the apparatus 
provides only mechanical actuators in the chamber, with a single easily 
sealed rotary shaft driving means. Electrical, air, or hydraulic devices 
within the chamber are avoided. 
To generalize, the invention provides indexing with both disengageable 
rotating and locking devices at all disk assembly stations, through 
rotation of the inner shaft from outside the chamber. In the inner shaft 
rest position all disks are locked for drilling; in moving to its actuated 
position the disks are unlocked and rotated to a nominal new position; in 
returning to its rest position, all disks are precisely located and 
locked. 
Generally each assembly on the housing is comprised of a disk which is 
coupled with a nominal rotating mechanism (the rack gear shaft, pawl, and 
teeth) and a precision locating mechanism, (the shot pin and disk cavity). 
The rotating and precision locating mechanisms are alternately actuated by 
a single driving member, the rack gear shaft. This simplicity is a feature 
of the invention. Other members rather than the rack gear may be used as 
the driving member, to obtain the requisite interrelated motion of the 
pawl-carrying shaft 22, line 30, and shot pin 18. That is any one of the 
three, interconnected elements (18, 30, and 22) may be driven, as by 
action of other gears, cams, or linkages, interconnected with the inner 
shaft 74. 
In use, the operator of the machine mounts each of the parts upon a disk, 
generally in the manner indicated by FIG. 3. The location of the airfoil 
44 with respect to the disk 64 is determined by keyed fixtures and disk 
assemblies. To set any disk to its starting position the operator actuates 
the cylinder to disengage the shot pin. He then manually disengages the 
pawl and freely rotates the disk. He then actuates the cylinder to engage 
the shot pin, locking an airfoil in the position desired for drilling the 
first row of holes. When all assemblies are set he advances the housing 
into the chamber. After evacuation, rotational and translational motion of 
the shaft 46 is employed to drillthe first row of holes. Then the cylinder 
78 is actuated to rotate the shaft 74 the 90 degrees previously determined 
as being necessary to rotate the disks to the nominal position for the 
next row. Then the cylinder motion is reversed and the shaft 74 is 
restored to its rest position thereby causing engagement of the shot pins 
with the disks. Thereafter the motion of the manipulator shaft is 
commenced again and the second row of holes is drilled. In like manner 
succeeding rows of holes are also drilled. Upon the completion of the 
desired drilling, the vacuum is broken and the manipulator is retracted 
from the chamber, to remove the parts. 
In the best practice of the invention, automatic processor control is used 
to speed the motion of the manipulator and the indexing mechanism. With 
suitable sensing devices and programming the aforementioned operations can 
be carried out at high speed and with a degree of simultaneity. Also, 
interlocks may be employed to insure that all the disks are in the same 
position, to avoid problems from operator error in setting the disks at 
the zero position or from failure of an individual assembly to index. 
Although this invention has been shown and described with respect to a 
preferred embodiment, it will be understood by those skilled in the art 
that various changes in form and detail thereof may be made without 
departing from the spirit and scope of the claimed invention.