Laser device for removing material from rotating object for dynamic balancin

Popick, H.

Roberts, D. L.

English

NASA Technical Reports Server

REPLY TO 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
T o t  USX/Scientific & Technical Information DivisLQn 
Attentiont ML8s Wknnie M, Morgan 
FROM: G P / O f f i c e  of Assistant General Counsel for 
Patent Matters 
SUBJECT: Announcement of NASA-Owned U. S. Patents i n  STAR 
In  accordance w i t h  the procedures agreed upon by Code GP 
and C o d e  U S I ,  the attached NASA-owned U. S. Patent is being 
forwarded fo r  abstracting and announcement in NASA STAR. 
U. S.  Patent  No. 
Government or 
Corporate Employee 
t 3,472,998 
: Korad Corporation 
New York, New York 
Supplementary Corporate 
Source (if applicable) : Union Carbide Corporation 
New York, New ,York 
NASA Patent Case No. t ME'S-11279 
NOTE - If this  patent cwers an invention made by a corporate 
employee of a NASA Contractor, the following i s  applicabler 
Yes 
Pursuant t o  Section 305(a) of the National Aeronautics and 
Space A c t ,  the name of the Administrator of NASA appears- on 
the first page of the patent; however, the name of the actual  
inventor (author) appears a t  the heading of Column No. 1 of 
ing the  words 
Copy sf Patent o i ted  above 
https://ntrs.nasa.gov/search.jsp?R=19710010925 2020-03-17T02:52:53+00:00Z
LASER APPARATUS FOR REMOVING MATERIAL F.U.01; RGTEITI:;5 OT;!.'. :; 
iled April ." 3, 1967 
3,472,998 United States Patent 0 atented Oct. 14, 1969 
1 
3,472,998 
LASER APPARATUS FOR REMOVING MATERIAL 
FROM ROTATING OBJECTS 
Harvey Popick, Canoga Park, and Donald L. Roberts, 
Thousand Oaks, Calif., assignors, by mesne assign- 
ments, to the United States of America as represented 
by the Administrator of the National Aeronautics and 
Soace Administration . -  
Filed Air. 3, 1967, Ser. No. 428,094 
Int. C1. B23k 9/04 
U.S. C1. 219-121 1 Claim 
ABSTRACT OF THE DISCLOSURE 
T h i s  disclosure relates to an apparatus for removing 
material from a rotating object such as a gyroscope wheel 
to effect dynamic balancing of the wheel. A laser beam 
is employed to remove the material and to this end the 
time of firing of the laser is made to correspond to a 
given position of the rotating object at which position the 
portion of the object from which material is to be removed 
intercepts the beam path of the laser. First and second 
power supply means are provided for the laser, the first 
charging networks pumping up the laser to  a threshold 
condition in response to a control signal received from 
transducing means connected to the rotating object. After 
the laser has reached a threshold condition, a second 
charging network is automatically connected to the laser 
to further pump the laser in response to a trigger signal 
received a delayed time period after the control signal. 
This delayed period is sufficient to permit the laser to 
reach a threshold condition. The second charging network 
is of a shorter time constant and higher voltage so that the 
laser pulse is narrow thereby providing a h e  degree of 
control over the material removed from the rotating ob- 
ject. 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronautics 
and Space Act of 1958, Public Law 85-568 (Stat. 435; 42 
U.S.C. 2457). 
This invention relates to an apparatus for removing 
material from rotating objects by means of laser radia- 
tion. 
Laser radiation has proved to be an ideal means for re- 
moving material from objects, particularly objects rotat- 
t h g  at high speed. The impingement of a laser pulse it- 
self on ip portion of an object rotating at a high speed 
will actually result in a cutting away or vaporization of 
a portion of the object and by controlling the intensity 
and pulse width of the laser radiation striking the object, 
the amount of material removed may be carefully con- 
trolled. Use of a laser for such material removing opera- 
tions is ideal in balancing gyroscope wheels since dynamic 
balancing can be carried out whiIe the object is ratating. 
Normally, the output radiation from a pulsed laser has 
a pulse width determined by the pumping characteristic 
curve which in turn depends on the time constant of the 
basic charging network for operating the light pump. In 
this respect, the laser must first be pumped to a threshold 
condition before lasing begins and by the time the laser 
has reached this threshold condition, the remaining power 
from the charging network for pumping follows a fairly 
shallow curve with the result that the output laser pulse 
itself i s  .fairly broad. While material may be removed by 
such a pulsed laser, the scar, particularly on high speed 
rotating objects, is relatively long because of the pulse 
width of the radiation and there is thus lacking a certain 
degree of control over the point of impingement and the 
amount of material removed from the object. 
With the foregoing considerations in mind, it is a pri- 
mary object of this invention to provide an improved ap- 
paratus for removing material from rotating objects where- 
in a laser system is provided in which an extremely nar- 
row or short pulse of radiation is caused to impinge on 
the rotating object to the end that a relatively short scar 
results and a finer degree of control over the impingement 
point and material removed can be realized. 
Briefly, this object is realized by providing first and 
second charging networks for the laser device itself. The 
10 first charging network is caused to pump the laser to a 
threshold condition in response to a control signal re- 
ceived from suitable transducing means coupled to the 
rotating object. This control signal occurs at a point in 
time when the portion of the object from which mate- 
15 rial is to be removed passes through the beam path of the 
laser. A trigger signal is then generated a delayed time pe- 
riod after the control signal corresponding to the point in 
time when the laser has been pumped to its threshold 
condition. This trigger signal serves to connect the second 
20 charging network to the laser so that energy from the 
second charging network is all pumped into the laser to 
effect the generation of the laser pulse. In this respect, 
the second charging network has a very short time con- 
stant so that the resulting laser pulse is relatively short 
25 with the attendant advantages of a short scar length and 
thus a finer degree of control over material removal. The 
apparatus is particularly useful with respect to very high 
speed rotating objects wherein accuracy in removal of 
material from portion of the object is extremely impor- 
A better understan'ding of the invention will be had by 
referring to the accompanying drawings, in which: 
FIGURE 1 is a schematic diagram partly in block form 
of the invention; and, 
FIGURE 2 illustrates wave forms useful in explaining 
Referring first to FIGURE 1, there is shown an object 
10 which may, for example, constitute a gyroscope wheel, 
mounted for rotation at 11 preparatory to carrying out a 
Cooperating with the rotating object are transducing 
means including a balancing machine 12 and timing cir- 
cuit 13. The balancing machine 12 includes suitable trans- 
ducers for converting unbalance forces into suitable elec- 
45 trical signals, these unbalance forces being generated 
dynamically unless the rotating wheel 10 is exactly 
dynamically balanced about its axis of rotation. The 
particular signals provided by the timing circuit 13 can 
be synchronized to correspond to the unbalance point of 
50 the wheel or portion of the wheel from which material 
should be removed in order to effect balancing by refer- 
encing the signals to a given angular position of the wheel 
10 from a fixed reference. A fixed reference signal may be 
provided from a stationary sensing means labeled REF, 
55 as shown. The arrangement is such that a control signal 
will be provided by the timing circuit 13 whenever an un- 
balanced portion of the wheel passes through a given point 
in space. 
The laser system for removing material from this por- 
00 tion in order to effect dynamic balancing of the wheel in- 
cludes a first power supply 14 and cooperating lamp trig- 
ger means. This means is connected to receive the con- 
trol signal from the timing circuit 13 through a lead 15, 
lamp control 14, and ionization initiator plate 17 disposed 
65 adjacent to the helical coils 18 of a flash lamp for the laser. 
As shown, the first power supply means 14 is arranged 
to pump the flash lamp upon discharge of the storage con- 
denser C1 through the inductor L and lead 19. For the 
particular apparatus illustrated, a five kv. power supply 
70 in conjunction with the storage condenser C1 and induc- 
tor L, will pump the laser to a threshold condition in ap- 
proximately three hundred microseconds. As stated, this 
30 tant. 
35 the operation of the invention of FIGURE I. 
40 dynamic balancing operation. 
3,472,998 
3 
pumPing %initiated by the control signal from the timing 
circuit 13. The power supply, condenser, and inductor con- 
stitute a first charging network. 
Firing of the laser rod 20 by means of the first charging 
network operating by itself will result in a pulse of radia- 
tion 21 impinging on the rotating device at a point 22 
which corresponds to the point through which a portion 
of the rotating object from which material is to be re- 
moved passes. With only the pumping supplied by 14, the 
pulse width of the radiation 21 is relatively wide and thus 
the scar on the rotating object a t  22 is relatively long. 
In accord with an important feature of this invention, 
the pulse width of the laser radiation 2% is made consider- 
ably shorter by employing a second charging network. 
Thus as illustrated in FIGURE 1, there is provided a 15 
switch means in the form of an ignitron tube 23 having its 
cathode 24 connected to the lead 19 to the flash lamp and 
its plate 25 connected to a second power supply shown at  
26. The storage condenser C2 with the second power sup- 
ply constitutes the second charging network and defines a 20 
considerably shorter time constant than the first charging 
network and further the applied voltage is considerably 
higher. The igniter for the ignitron tube 23 is indicated 
at  27 and connects to the output of a delay circuit 28 in 
turn receiving the control signal from the timing circuit 25 
13 through the lead 29. 
The control signal received in the delay 28 is the same 
control signal passed through the lead 15 to initiate lamp 
operation. The delay 28 provides an output signal which 
is delayed in time to a point corresponding to the length 30 
of time for the laser rod 20 to be pumped to threshold 
condition. This output signal constitutes a trigger signal 
for the ignitron tube 23 and when received on the igniter 
terminal 27, the second power supply 26 will be con- 
nected to additionally pump the laser 20 for an intense 35 
short period of time thereby providing the desired nar- 
row pulse. 
The foregoing operation will be better understood by 
now referring to FIGURE 2.  In the lower wave foim of 
FIGURE 2, there is shown a control pulse 30 which con- 40 
stitutes the control signal from the timing circuit 13. When 
this signal is passed to the lamp control 16 at the time fl, 
the spiral flash lamp commences pumping the laser rod 
20, the pumping curve being illustrated in the upper wave 
form at 31. At the time fa, the pumping curve has reached 45 
a magnitude T which corresponds to the threshold of 
operation of the laser. At this time fa, the trigger pulse 
from the delay 28 indicated at 32 in FIGURE 2 will close 
the ignitron switch 23 thereby providing additional pump- 
ing from the second power supply 26 to the flash lamp. 60 
The additional pumping curve is illustrated at  33 and has 
a considerably narrow width w because of the shorter 
time constant of the power supply. Thus, with the second 
power supply provided, the pulse width of the laser pulse 
of radiation 21 of FIGURE 1 will be considerably nar- 55 
rower resulting in a shorter scar 22 on the rotating ob- 
ject 10. 
Jt will be apparent accordingly that the apparatus en- 
ables a finer degree of control to be realized over the 
amount of material removed as well as a pin-pointing of 60 
the exact location on the rotation object from which mate- 
rial i s  to be removed. In this respect, the timing of the 
control and trigger pulses is extremely important. For ex- 
ample, period P between il and tz in FXGURE 2 may be 
of the order of three hundred microseconds. The pulse 65 
width w in turn may be of the order of four to forty micro- 
seconds. The period P corresponds to the time to pump 
the laser rod to a threshold condition and thus in the em- 
bodiment illustrated in FIGURE 1, the delay circuit 28 
4 
will be set to provide a trigger pulse at exactly this time 
period after the control pulse is received. The directing 
of the laser rod 20 can be adjusted to  take into account the 
r.p.m. of the rotating object such as to precisely have its 
beam impinge on the desired unbalance point of the rotat- 
ing object from which material is to be removed. This 
particular point will be directly in the path of the beam 
at  the time t2 when the trigger pulse 32 closes the ignitron 
tube switch 23 to provide the additional pumping for the 
laser rod thereby effecting laser operation. 
In the circuit of FIGURE 1, the trigger pulse is de- 
rived from the control pulse by means of the delay 28. 
It will be understood of course, that a lamp current sens- 
ing coil could be employed to  provide the trigger pulse 
32 only when the lamp current corresponded to that re- 
sulting when a threshold condition of the laser rod 20 is 
attained. 
From the foregoing description, it will be evident that 
the present invention has provided an improved laser ap- 
paratus for removing material from rotating objects where- 
in the desired ends of accuracy and finer control of ma- 
terial removal are realized. 
What is claimed is: 
1. An apparatus for removing material from a rotat- 
ing object, comprising, in combination: a laser medium 
positioned to direct its beam when fired at  a given point 
in space through which a portion of said object from 
which material is to be removed passes when said object 
is rotating; transducer means responsive to rotation of said 
object for providing a control signal when said portion 
passes said point; a flash lamp optically coupled to said 
laser medium; a first charging nelwork connected to said 
flash lamp for pumping said laser medium with light 
energy from said flash lamp to a threshold condition in 
response to said control signal; means for generating a 
trigger signal at a point in time when said laser medium 
reaches said threshold condition; a second charging net- 
work connected to said flash lamp for providing pump- 
ing energy of higher voltage and shorter time constant 
than said first charging network; normally open switch 
means connected between said second charging network 
and said flash lamp and responsive to said trigger signal 
to close such that said laser medium is additionally 
pumped by light from said flash lamp generated by power 
from said second charging network to provide laser radi- 
ation of narrower pulse width than would occur in the 
absence of said second charging network to result in a 
shorter scar length of material removed from said por- 
tion and thereby provide a finer degree of control of the 
material removed; said means for generating a trigger 
signal including delay means receiving said control signal 
and designed to provide an output signal a given time 
delay after said control signal corresponding to  the time 
to attain said threshold condition, said output signal de- 
fining said trigger signal. 
References Cited 
UNITED STATES PATENTS 
3,172,056 311965 Stitch _ _ _ _ _ _ _ _ _ _ _ _ _ _  331-94.5 
3,178,657 4/1965 Morse _ _ _ _ _ _ _ _ _ _ _ _ _  331-94.5 
3,259,730 7/1966 Wehde et al. 
3,199,049 8/1965 Morse et al. _ _ _ _ _ _ _ _  331-94.5 
JOSEPH V. TRUHE, Primary Examiner 
W. DEXTER BROOKS, Assistant Examiner 
U.S. C1. X.R. 
2 19-69 


Laser apparatus for removing material from rotating objects Patent

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