Autonomous selective cutting method and apparatus

Real time in-process data is collected to determine the contour and position of the interface between dissimilar layers of material. A control system is automatically programmed, based on the determined contour and position of the interface, to autonomously control the trajectory of a cutter through a conventional motion control system to separate the dissimilar layers of material. The motion control system controls the cutter movement through, for example, a conventional linear motion device including a servomotor, lead screw, and slidable carriage that holds the cutter.

BACKGROUND OF THE INVENTION 
The invention relates to cutting generally, and more specifically to 
autonomously controlling the position of a cutting tool to selectively 
remove one layer of material from a dissimilar layer of material. 
Selective cutting generally involves removing an undesired layer of 
material from a desired layer. In conventional machine tools, including 
machine tools of the numerical control (NC) and computer numerical control 
(CNC) type, a cutting tool typically is mounted on a carriage which is 
moved by a motor driving the carriage through a lead screw. Typically, 
control signals are supplied to the motor by a motion control system to 
control the cutting path of the cutting tool. In this way, the tool can 
automatically machine a rotating workpiece, for example, to a 
predetermined profile. However, since the cutting path of the 
predetermined profile must be pre-programmed into the system, it must be 
known in advance of the cutting. This is a problem in selective cutting 
applications where the location of the interface between dissimilar layers 
of material to be separated is not known. Accordingly, selective cutting 
generally has been limited to manual operations. However, in manual 
operations operator error can result in over extension of the cutter and 
damage to the desired layer. 
SUMMARY OF THE INVENTION 
The present invention is directed to a selective cutting method and system 
that avoids the problems and disadvantages of the prior art. This goal is 
accomplished by providing a system that autonomously scans a particular 
workpiece to be cut and collects real-time in-process data relating to 
features of that workpiece. The system processes that data and generates a 
program to autonomously control the trajectory of a cutter to selectively 
remove an undesirable layer of material from the workpiece, for example. 
According to a preferred embodiment, a structure having first and second 
dissimilar layers of material is provided with one layer disposed on the 
other. The structure is scanned and the position of points on the first 
and second layers of material is detected by a laser optics system, for 
example, and fed into a processor. Based on the detected position of the 
points, the processor autonomously generates data indicative of the 
position and contour of the surface of the first layer adjacent the second 
according to an algorithm. That is, the processor processes the digitized 
samples and generates, corrected samples that represent the position of 
the aforementioned first layer surface. Based on the processed data, the 
processor then autonomously controls the position of a cutter to follow 
the surface of the first layer adjacent the second layer and remove the 
second layer from the first layer. Accordingly, the present invention 
provides autonomous selective cutting of dissimilar layers of material, 
when the interface between those layers is unknown before cutting. 
The use of real-time data also permits the system to accurately remove a 
layer of material from another layer having substantial variances in 
thickness or being out-of-round, for example. In addition, the autonomous 
acquisition of real-time data allows the system to readily adapt to 
different applications where the layer characteristics and configuration 
significantly differ from workpiece to workpiece. 
Another advantage of the real-time acquisition of data specific to a given 
workpiece is that it allows the system to accommodate applications where 
poor set-up or fit-up of the workpiece is involved (e.g., where a 
cylindrical member is not concentrically positioned on a lathe) or where 
the workpiece is noncylindrical. This provides significant reduction in 
set-up costs since the system can accommodate poor set-up. Specifically, a 
method for cutting a rotating workpiece at a constant depth according to 
the present invention comprises the steps of providing a workpiece on a 
workpiece holder, scanning the outer peripheral surface of the workpiece 
(i.e., the surface to be cut such as the outer cylindrical surface of a 
cylindrical workpiece) and detecting points representing that surface, 
rotating the workpiece holder and, thus, the workpiece, and autonomously 
controlling the position of a cutter based upon the points detected in the 
scanning step such that the cutter follows a path parallel to the contour 
of the peripheral surface and at a constant depth in the workpiece. Thus, 
the cutter is maintained at a constant depth even though the workpiece may 
be mounted on the workpiece holder such that the peripheral surface of the 
workpiece is not concentric with the rotational axis of the workpiece 
holder. 
The above is a brief description of some deficiencies in the prior art and 
advantages of the present invention. Other features, advantages and 
embodiments of the invention will be apparent to those skilled in the art 
from the following description, accompanying drawings and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings in detail, wherein like numerals indicate like 
elements, a selective autonomous cutting method and system in accordance 
with the principles of the present invention will be described, Referring 
to FIG. 1, a cutting head 2 and control system 4 for autonomously 
separating dissimilar layers of material is shown according to the present 
invention. Cutting head 2 includes a cutting tool, a servomotor for 
reciprocating the cutting tool, and optical sensors. Control system 4 
includes a central processing unit (CPU) and a conventional display, power 
distribution system and operator interface (e.g., a remote go-stop control 
unit). The optical sensors are coupled to the CPU which, in turn, is 
coupled to the servomotor system for autonomously controlling the 
trajectory of the cutting tool based on data gathered from the sensors, as 
will be described in more detail below. 
Cutting head 2 includes a casing 6 (shown in phantom) which houses the 
cutting tool mount 8, cutting tool carriage 10, drive 12, light or laser 
emitters 14, 18 and photosensors 16, 20. Cutting tool mount 8 is fixedly 
secured to the casing and includes a flange 22 which is preferably 
dimensioned to fit into a conventional adjustable tool post of a 
conventional machine tool lathe. In this way, the cutting head is 
retrofitable onto a conventional lathe. Carriage 10 is slidably coupled to 
cutting tool mount 8 so that the carriage can be reciprocated back and 
forth. Preferably, the bottom portion of cutting tool mount 8 and the 
upper portion of the carriage are configured to provide a dove-tail slide 
mechanism therebetween. In the embodiment illustrated in FIG. 1, cutting 
tool mount 8 includes fan-shaped tenon 24 which fits into corresponding 
mortise 26 formed in the carriage. Cutting tool holder 28 extends from one 
end of carriage 10 and includes cutting tip or cutter 30 which preferably 
is detachably mounted to the cutting tool holder as is conventional in the 
art. Cutting tip 30 also preferably includes a conventional insert such as 
a carbide insert. The insert composition generally selected according to 
the workpiece material as would be apparent to one of skill in the art. 
One suitable cutting tip insert is commercially available from Kennemetal, 
Inc. of Latrobe, Pa., under model no. TNMG332-KC730. 
Carriage 10 and, thus, cutting tip 30, are reciprocated by drive 12, which 
preferably is a servomotor, and lead screw 32 as is conventional in the 
art. Lead screw 32 is rotatably coupled to planetary nut 34 (FIG. 2) 
which, in turn, is fixedly secured to carriage 10. One suitable planetary 
nut it commercially available from ITW Spiroid of Chicago, Ill. under 
model "Spiracon" roller screw and nut. In this way, rotation of lead screw 
32 linearly displaces carriage 10 either forward or backward, depending on 
the direction of rotation of the screw. Lead screw 32 is coupled to the 
output shaft 36 of servomotor 12 through a conventional zero-backlash 
coupling 38. Servomotor 12, which is fixedly secured within casing 6, is 
provided with a conventional encoder 40 for counting the revolutions of 
the shaft. In this way, the position of cutting tip 30 can be monitored at 
all times. Motor control line 42 for actuating and deactuating the motor, 
and encoder signal line 46, are connected to the CPU. Each line comprises 
a plurality of leads as is conventional in the art. The central processing 
unit processes the signals from the encoder to determine the position of 
the cutting tip and control rotation of the servomotor through control 
line 42. 
As described above, cutting head 2 includes light or laser emitters 14, 18, 
and photosensors 16, 20. Emitter and photosensor pair 14 and 16 are used 
to determine the RPM and detect each revolution of the workpiece being 
cut, while emitter and photosensor pair 18 and 20 are used to scan the 
workpiece and detect (or sense) the distance between the points on the 
surfaces of the first and second layers of the workpiece and 
photosensitizer 20 or some other datum point. Emitter 14 and photosensor 
16 are of conventional design and are coupled to preamplifier 48 which 
includes a driver for emitter 14. Signals indicative of an "on" condition 
are transmitted to the CPU from photosensor 16 and preamplifier 48 through 
line 50 which also couples the driver of preamplifier 48 to the control 
system. As illustrated in FIG. 1, emitter 14 emits a light or laser beam, 
designated by reference number 52, which is reflected by mirror or prism 
54 arranged at an angle of about 45 degrees relative to the path of beam 
52, for example, such that beam 52 is directed toward reflective strip 56 
when strip 56 is in the position shown in FIG. 1. The reflected beam 58 is 
then directed to the photosensor 16 by mirror or prism 54. Photosensor 16 
then sends a signal through preamplifier 48 and lead 50 to the CPU 
indicative of an "on" condition. Light-reflective strip 56, having a 
surface made of micro-glass beads, for example, is attached to either 
workpiece 60 or workpiece holder 62 of a lathe, for example. As the 
workpiece rotates in the direction of arrow 64 the reflective strip 56 
also rotates such that receiving photosensor 16 detects each revolution of 
the workpiece when the reflective strip comes into alignment with emitted 
beam 52. Any suitable emitter and photosensor can be used such as those 
commercially available from Banner Engineering of Minneapolis, Minn., 
under model number SM312LV and BRT-T-100, respectively. 
The second optical sensing system includes light or laser emitter 18 and 
triangulation photosensor 20, both of conventional design. For example, 
emitters and photosensors commercially available from Keyence of Japan 
under model number LC 2100 are suitable. Emitter 18 emits a beam 66 
preferably having a minimum spot diameter of about 0.2 millimeter. Beam 66 
is reflected off the workpiece 60 as designated by reference numeral 68 
and received by photosensor 20. Photosensor 20 includes a conventional 
photosensitive strip of material having a resistance that varies as a 
function of the location of the reflected beam along the longitudinal axis 
of the strip. The photosensitive strip is oriented in the same plane as 
the incident and reflected laser beams 66, 68. In addition, the angle of 
the incident laser beam and the orientation of the photosensitive strip 
preferably are arranged such that the reflected beam strikes the 
photosensitive strip at a point in the middle region of the strip. Laser 
beam emitter 18 is coupled to conventional laser beam driver 70 (which is 
coupled to the control system through line 74), while photosensor 20 is 
coupled to amplifier 72 (which is coupled to the CPU through line 76). The 
control system determines the position and path of consecutively detected 
points on the workpiece by noting the path of the laser beam along the 
axis of the elongated strip as the workpiece is rotated. For example, if 
the detected points follow a cylindrical path, the reflected laser beam 
will stay approximately in the middle region of the photosensitive strip. 
However, if the detected points follow an elliptical path, the laser beam 
will reciprocate up and down the axis of the photosensitive strip as the 
major axis and then the minor axis of the elliptical path traverses laser 
beam 66. 
Cutting head 2 also is provided with a system for limiting the linear 
translation of carriage 10 and, thus, cutting tip 30. This limiting system 
includes guillotine 78 which is fixedly secured to carriage 10, forward 
limit sensor 80, and rearward limit sensor 82. Sensors 80 and 82 are 
coupled to a driver 84 to generate a light beam between the legs of the 
U-shaped sensors 80 and 82. Driver 84 also includes electronics for 
detecting the interruption of the laser beam between the legs of either of 
the U-shaped sensors 80 and 82 by guillotine 78 when carriage 10 travels 
to the extent that the guillotine is positioned within one of those 
sensors. Driver and interruption detector 84 is coupled to the CPU as 
designated by line 76. The control system processes signals received from 
detector 84 and deactivates the motor when the carriage is moved to these 
limits. This ensures that the carriage will not fly out of cutting tool 
mount 8 and, in addition, detects a problem in the motion control program 
which will be described in more detail below. Although a conventional 
guillotine-type limit sensing system is illustrated in FIG. 1, other limit 
sensing systems can be used without departing from the scope of the 
present invention. 
In operation, the CPU receives and analyzes the real-time data transmitted 
by sensors 16 and 20 in order to determine and execute the desired 
trajectory of cutting tip 30 through a conventional motion control system 
that is incorporated into control system 4. In the first step of analyzing 
the information from optical sensors 16 and 20, the workpiece is rotated 
and the CPU digitizes the data from the sensors and then filters and 
discards nonsignificant data and noise according to an algorithm as will 
be described in more detail below with reference to the example 
illustrated in FIGS. 3-9. After the CPU carries out the algorithm and 
determines the position and contour of the surface of the first material 
from which the second material is to be removed, it goes on to plan the 
trajectory of the cutting tip for the final cutting of the workpiece to 
remove the undesired second layer and any faults (such as bumps on the 
first layer). That is, the information gathered by the photosensors is 
translated by the CPU into a program which is used to control the 
trajectory of the cutting tip through the motion control system during the 
final cut. 
In the case where a constant depth of cut into the peripheral surface of 
the workpiece (which may be generally smooth, for example) is desired, 
photosensor 20 detects the points on that surface as the workpiece is 
rotated and the CPU processes that information (i.e., the distance between 
those points and a datum point) to map the profile or contour of that 
surface. As the workpiece is rotated, the control system controls the 
position of the cutter to follow a path parallel to the contour of that 
surface at a constant depth in the workpiece. 
Merely to illustrate how the algorithm is developed in accordance with the 
present invention, the following example case is provided in which an 
undesired layer of honeycomb is removed from the smooth underlying 
metallic surface. However, it should be understood that the following 
example is in no way intended to limit the scope of the present invention. 
Referring to FIGS. 3 and 4, a jet engine part 88 having a layer of 
honeycomb 90 superimposed upon a smooth underlying metallic surface, i.e., 
base metal 92, is shown. For purposes of illustration, a portion of the 
honeycomb is shown removed as by the selective cutting system of the 
present invention (FIG. 3). Honeycomb 90 comprises a plurality of cells 93 
some of which may be partially or wholly plugged, for example, as 
indicated by reference numeral 94. Although jet part 88 can be in the form 
of a ring segment or a full ring, for example, it is shown as having a 
ring-shaped configuration in FIG. 5. Part 88 is further shown secured to 
the inside of ring fixture 96 so that it can be mounted to the workpiece 
holder of a conventional lathe for rotation therewith. As would be 
apparent to one of ordinary skill, the laser emitters, photosensors and 
cutter would be arranged so that the laser beams and cutter would approach 
part 88 from the inside of the ring. Referring to FIG. 6, as part 88 is 
rotated, incident laser beams 66 will reflect off of the upper surface 100 
of base metal 92 (i.e., the interface between the undesirable layer 90 of 
honeycomb and the base metal layer 92), cell walls 102 of the honeycomb, 
and other features of the composite structure such as material 94 that may 
obstruct a particular cell. FIG. 7 illustrates the data obtained from the 
reflection patterns shown in FIG. 6 in ideal conditions where the X-axis 
represents time and the Y-axis represents the distance between the point 
of incidence in the workpiece and a datum or reference point "d" which 
preferably is at photosensor 20 The O-coordinate corresponds to the 
position of upper surface 100 of base metal 92. However, actual 
conditions, noise and inconsistencies in the honeycomb, such as 
obstructions 94 in the cells, cause the signals received by photosensor 20 
and sent to the CPU to generate a much more complex pattern as illustrated 
in FIG. 8. It then becomes more difficult to determine the exact position 
of the base metal. The present invention incorporates an algorithm 
described below so that the CPU can process the information, such as that 
illustrated in FIG. 8, to determine the exact position and contour of the 
base metal. The position of the upper surface of base metal 92 (determined 
according to the present invention) is shown by line 104 in FIG. 8 to 
illustrate the relationship between significant and insignificant data. 
The autonomous separation of dissimilar materials (e.g., honeycomb 90 and 
base metal 92) generally is carried out in two steps: a precut (or rough 
cut), during which the part to be cut is simultaneously scanned by 
photosensor 20 and the real-time data digitized and sent to the CPU, and a 
final cut, during which the control system controls the trajectory of the 
cutter 30 to precisely follow the surface of the base metal based on the 
information gathered during the precut and processed by the CPU. 
That is, the CPU processes this data during a first rough cut to determine 
the position of the base material and autonomously generates a program, 
which it runs during a final cut, to control the motion of the cutting tip 
and remove the layer of honeycomb from base metal 92 as will be described 
in more detail below. 
In the first step or precut, the cutter preferably is positioned such that 
it penetrates into the honeycomb by at least about 50% the thickness of 
the honeycomb and preferably near 100% the thickness of the honeycomb with 
a minimal amount of honeycomb remaining between the cutter and base metal 
92. This degree of penetration will vary according to how out-of-round the 
workpiece is, for example. Although it is not necessary that the cutter be 
positioned to cut any material in this scanning step in accordance with 
the present invention, when the rough cut is performed while scanning, a 
subsequent rough cut step is avoided which is clearly advantageous. Once 
the cutter is positioned for the rough cut, according to the preferred 
method for this example, the motor and encoder are deactuated so that the 
cutter remains stationary relative to the cutting head throughout the 
scanning and data gathering step. Thus, the cutter does not reciprocate 
and appears to behave like a standard cutter to the machinist. Then, laser 
emitters 14, 16, photosensors 16 and 20 are actuated, the work piece 
holder is rotated such that ring fixture 96 is rotated therewith, and 
cutter head 2 (through its tool post described above) is moved along a 
straight path so that cutter 30 moves substantially parallel to the 
rotational axis of ring fixture 96 (i.e., gradually across the width of 
parts 88) at a substantially constant feed rate. An adjustable feed 
mechanism associated with the tool post, as is conventional in the 
machining art, can be used. Thus, as ring fixture 96 rotates and cutter 30 
is fed along the inner surface of fixture 96, cutter 30 cuts a spiral 
path. In addition, emitter 18 directs a laser beam at the inner surface of 
fixture 96 so that the point of incidence of the loser beam leads the 
cutter so that photosensor 20 detects the characteristics of the part 
along the spiral path that the cutter will follow. Thus, a number of 
frames data, each corresponding to one revolution of fixture 96, is 
collected by the CPU. 
Ring fixture 96 is provided with a reflective strip, such as strip 56, 
which is orientated such that photosensor 16 senses the beginning and end 
of each revolution of the fixture as described above. Thus, the reflective 
strip can be attached to the edge of fixture 96 so as to extend therefrom 
in a direction generally perpendicular to the rotational axis of the 
fixture. Preamplifier 48 sends signals to the CPU, each representing a 
revolution of fixture 96, The CPU processes this information with the 
information detected by photosensor 20 and generates a matrix. Thus, the 
distance between each sensed point on part 88 and photosensor 20 (i.e., 
sampling) is put into the matrix according to the angular position of a 
sensed point within a frame (i.e., a 360.degree. revolution). In the 
example case where the radius of part 88 is about 15 inches, the distance 
between sensed points in a frame in the matrix is in the range of about 
0.1.degree.-0.001.degree. depending on the workpiece RPM. It has been 
found that at about 30 RPM this distance preferably is about 0.05.degree.. 
A sensed point, thus, can represent the base metal 92, the wall of a 
honeycomb cell 93, the upper edge of a honeycomb cell, or an obstruction 
94 or some other imperfection. Thus, the CPU must verify whether or not 
each distance represented in the matrix is a valid representation of the 
distance between the base metal 92 and photosensor 20. The algorithm used 
to make this determination will be described with reference to the example 
CPU generated matrix illustrated in FIG. 9. 
Referring to FIG. 9, the angular orientation (.alpha.) of each sensed point 
is indicated along the top row and the frame number is indicated along the 
left column. For purposes of simplification, only 11 consecutive points 
and 5 frames are shown. In addition, the actual values of the samplings 
(as opposed to binary code) are shown for illustrative purposes. The 
numerals in the matrix representing .alpha. correspond to positions at 
0.05, 0.10, 0.15, 0.20, 0.25, etc. from the beginning of a particular 
frame. During verification, each piece of information in the matrix 
indicating distance is compared with each adjacent piece of information. 
If the difference between the piece of information being verified and a 
compared piece of information does not exceed a predetermined value, the 
piece of information being verified is kept in memory as the distance 
between the base metal and photosensor 20 at its particular location on a 
respective part 88. Through experimentation it has been found that the 
difference discussed above should not exceed about 0.004 inch, and 
preferably should not exceed about 0.002 inch, for honeycomb having a cell 
height of about 0.25 inch, and a cell density of about 500-1000 
cells/in.sup.2. For example, referring to the circled 1.000 inch distance 
shown in FIG. 9 at 0.20.degree. (.alpha.no. 4) from the beginning of frame 
3, none of the adjacent data (1.000, 1.001, 1.000, 1.001, 1.000, 1.000, 
1.998, 1.002) differs from the 1.0 inch distance being verified by more 
than 0.004 inches. Thus, the circled value is kept in memory as a valid 
distance. However, this is not the case for the 1.200 inch distance shown 
at 0.50.degree. (.alpha.no. 10) from the beginning of frame 2. Adjacent to 
this data is 1.000, 1.000, 1.100, 1.000, 1.200, 1.000, 1.000 and 1.200. 
Since the data being verified (1.200) differs from at least one adjacent 
piece of information for sampling by more than 0.004 inch it is dumped 
from memory and replaced with the value corresponding to the last verified 
data in frame 2 (i.e., 1.000), unless a sufficient number of subsequent 
values in frame 2 verifies the 1.200 value. In the latter case, the 1.200 
value is kept in memory as a valid distance between base metal 92 and 
photosensor 20. That is, the subsequent data can verify that the distance 
between base metal 92 and photosensor 20 actually increased more than 
0.004 inch. It has been found that the required number of consecutive 
verifying values for the example case is about 10-100, and preferably 
about 40 values, to provide the desired cutting accuracy. Thus, if the 
difference between adjacent verifying values for the subsequent 40 
consecutive values, for example, does not exceed 0.004 inch, the sample 
being verified is considered good and kept in memory. However, if a 
difference between any adjacent values exceeds 0.004 inch throughout the 
entire verifying group the value undergoing verification is dumped and 
replaced with the preceding value. In this way, the contour of the base 
material of the workpiece is determined exclusively by the information 
generated by photosensor 20. The information generated by photosensor 16 
is used to flag the beginning of each revolution of the workpiece so that 
the CPU can compare two or more adjacent contours (as shown in adjacent 
frames in FIG. 9) of the workpiece. 
Based on the verified data representing the position of the base metal 
relative to photosensor 20 and the distance between photosensor 20 and 
cutter 30 when at a zero reference position, the CPU generates a program 
for the motion control system that is provided within control system 4. 
The motion control system is of conventional design. The program runs the 
motion control system during the final cut to control the trajectory of 
cutter 30 and remove the honeycomb material without removing base metal 
92. 
Referring to FIGS. 10-13 and 14A-C, simplified flow charts illustrating a 
method of carrying out the invention are shown. FIG. 10 illustrates the 
overall autonomous selective cutting process, while FIGS. 11, 12, 13 and 
14 illustrate the edge detection, correction, precut, and finish cut 
subroutines. Referring to FIG. 1, the operator actuates a start button 
which initiates a standard self test which includes testing the CPU, and 
the servomotor, for example. The limit sensors 80 and 82 are tested. Then 
the operator determines whether the workpiece is a continuous ring or a 
segmented ring. If it is a segmented ring, then the edge detection 
subroutine is used to differentiate data obtained between adjacent segment 
edges from other data and eliminating the data gathered between those 
edges. However, if the workpiece is in the form of a continuous ring, the 
emitters and photosensors are actuated for data collection which 
optionally includes a precut step. The collected data, representative of 
points on the workpiece, is smoothed and the smooth data written out so 
that the data points indicative of the desired trajectory of the cutter 
can be used during the finish cut to position the cutter to remove the 
undesired material. 
Referring to FIG. 11, the edge detection includes the steps of shifting the 
data in a time domain, subtracting the shifting data from the original 
data, marking the places where the difference exceeds a specific value and 
writing out the position and direction of the difference. The correction 
step shown in FIG. 12 includes reading in the data points or samplings, 
reading in the correction table which includes the verification steps 
described with reference to the algorithm discussed above, remapping the 
data points to provide a program to control the intended trajectory or the 
cutter, and writing the remapped data points to a disk. 
The combined collecting, smoothing and precut process is shown in FIG. 13, 
where the operator is first asked for the diameter of the workpiece since 
this will determine the depth to which the cutter is initially positioned 
into the layer of material being removed. The diameter is read into the 
CPU and then the operator waits for a stable RPM of the workpiece. Once 
the workpiece RPM has stabilized, the operator pushes go to begin the 
precut. During the precut data is collected for one revolution and that 
data displayed, corrected, and summarized. If the operator does not push 
the stop button, the workpiece continues to rotate and data is collected 
for another revolution and that data displayed, corrected and summarized. 
When all of the data necessary to be collected is collected, the operator 
pushes the stop button and a final summary of the corrected data is made. 
Then, the workpiece is ready for a finished cut. As shown in FIGS. 14A-C, 
the operator pushes the start button for finish cut, and the desired 
trajectory of the cutter is read into the CPU. The trajectory of the 
cutter is then adjusted according to the set-up and geometric 
characteristics of the workpiece including its diameter. This is to 
compensate parallax between the cutter and laser sensor 20 centerlines. 
The system then tells the user that the set-up is ready for rotation. Once 
it is confirmed that the lathe is rotating, the system tells the user to 
proceed with the finish cut. At that point the user decides whether to 
proceed with the finish cut or whether to cancel that operation. If the 
user determines to proceed with the finish cut, the cutter is moved to the 
given trajectory in synchronization with rotation at which time the CPU 
takes over control of the cutter to control its position in accordance 
with the collected and smoothed data. The process is aborted if the user 
decides to stop the operation, the lathe rotation becomes unstable or it 
stops, motion error is detected, and electronics error is detected or a 
power failure is detected. 
Although the invention has been described with respect to a part having a 
layer of honeycomb and a smooth base metal layer, the invention can be 
applied to numerous other applications where it is desirable to remove one 
material from another, or merely to remove material from its environment. 
In addition, the sensed characteristic of the workpiece surface can differ 
from that described. For example, it can be color, color gradients, 
density, conductivity, roughness, or any combination of these or other 
physical properties. Then the algorithm verifying the validity of 
collected data is modified accordingly. For example, if the surface of the 
undesired layer is relatively rougher than the surface of the underlying 
desired layer, the width of the reflective beam will be wider (more 
scattered) when reflecting off the undesired layer versus the desired 
layer. The pattern recognition subroutines or algorithm of the CPU will be 
modified to interpret the scattering to mean that the beam is focused on 
the undesired layer. Further, the workpiece or structure to be cut is not 
limited to those having a circular configuration as shown in FIG. 1 as 
would be apparent to one of ordinary skill. 
As is apparent from the foregoing, the present invention has many diverse 
applications. For example, it is contemplated that the cutting head be 
incorporated into a catheter for removing plaque from the wall of the 
artery. In this case, the sensed property preferably would be density and 
the sensing medium preferably ultrasound. The cutter also can be provided 
with three-dimensional movement so that it can selectively remove cancer 
cells from healthy cells in a patient. It is also contemplated to use 
selective cutting system of the present invention in the shipping industry 
where it can be used to remove barnacles from ship hulls, for example. 
This is especially advantageous to avoid reduction in hull speed and 
visibility to enemy sonar due to turbulent flow created by the barnacles. 
In a similar way, the invention can be used to remove paint from an 
underlying surface. It is also contemplated that the present invention has 
application in agriculture to sense ripe fruit on a tree and direct a 
cutter mounted on a large flexible hose to that particular fruit to cut 
the fruit so that it falls through the hose into a receptacle. 
The system and method of the present invention also can be used in 
semi-conductor fabrication. In that case, it would be used to remove a 
certain amount of dielectric insulator deposited over an active layer to 
ensure that the insulation layer is truly flat before positioning another 
active layer upon the insulator when fabricating a chip. Generally, when 
building a chip, the active layer is provided. A passive layer is 
deposited on that active layer by plasma deposition, for example. The 
dielectric layer ends up having a three-dimensional terrain due to the 
configuration of the transistors in the active layer. Since the dielectric 
layer comprises glassy material, the system is programmed to detect the 
deepest depression that does not penetrate below the highest point on the 
active layer. The deepest point of that depression is then used to set the 
position of the cutting apparatus to remove all insulator material above 
that location, resulting in a flat surface of the insulator material. 
The above is a detailed description of a particular embodiment of the 
invention. It is recognized that departures from the disclosed embodiment 
may be made within the scope of the invention and that obvious 
modifications will occur to a person skilled in the art. The full scope of 
the invention is set out in the claims that follow and their equivalents. 
Accordingly, the claims and specification should not be construed to 
unduly narrow the full scope of protection to which the invention is 
entitled.