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Патент USA US3063708

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Nov. 13, 1962
L. J. HANCOCK
3,063,698
PHOTOELECTRIC CONTROLLED LINE FOLLOWING DEVICES
Filed June 1, 1960
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726/7
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AS USED WITH OXYGEN JET CUTTING MACHINES
2 Sheets-Sheet 1
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LEsL‘l E
Inventor
J. HANC ocK
By \ _ \¢ g .
‘:
Attorney
Nov. 13, 1962
L. J. HANCOCK
3,063,698
PHOTOELECTRIC CONTROLLED LINE FOLLOWING DEVICES
AS USED WITH OXYGEN JET CUTTING MACHINES
FiledJune 1, 1960
2 Sheets-Sheet 2
-
LESLI'E J'- HANCOCK
1n venlor
60
By MA:torneys
United States Patent() ” 1C6
3,963,598
liar-tented Nov. 13, 1962
2
3,063,698
PHOTQELECTRIC CONTROLLED LINE FOLLOW
ENG DEVICES AS USED WITH OXYGEN JET
CUTTING MACHENES
Leslie John Hancock, Puriey, England, assignor to Han
cock & Co. (Engineers) Limited, Croydon, England, a
British company
tion of the outline so that it alternately “looks” at one
side and the other side of the outline. It is provided with
a small aperture so that it only scans a small area at one
time.
As the photoelectric cell moves from its central posi
tion to one side of the outline it develops a signal which
rises from a level corresponding to the dark area of the
outline and this signal increases as the photoelectric cell
Filed June 1, 1960, Ser. No. 33,192
Claims priority, application Great Britain June 1, 1959
moves until it reaches a maximum when the photo—
7 Claims. (Cl. 266-23)
10 electric cell is “looking” entirely at the brightly illumi
nated area at the side of the outline. As it swings back
to the centre the signal diminishes to its original low
level and after it has crossed the outline the signal rises
again to a maximum and thereafter again falls to zero
outline, or the edge of an outline or area, to control the
steering of a movable cutter in an oyxgen jet cutting 15 as the cell returns to its central positon. It is convenient
to vibrate the arm carrying the photoelectric cell at the
machine, the following device turning on its axis, which
mains frequency and a little consideration will show that
is substantially perpendicular to the plane of the out
the photoelectric cell produces a signal which rises from
line, to an extent depending upon the deviation of the
This invention relates to photoelectrically controlled
outline or edge following devices, and more particularly
to a photoelectric following device which follows an
outline from the straight line which is instantly being
followed by the following device.
Following devices now in use in oxygen jet cutting
machines rely either on the amount of light re?ected
from a drawing in which the outline is in the form of
a thick black line, the following device always adjusting
a low level to a high level and back to zero twice in each
cycle of the mains frequency; for example, if the mains
frequency is 60 c./s. then the signal from the photo
electric cell consists of 120 unidirectional impulses per
second. In fact, the output signal from the photoelec
tric cell is similar to the voltage wave which is obtained
itself so that a projected spot of light is half over the 25 by rectifying the mains frequency through a full wave
recti?er.
line, or on the scanning of a short path transverse to
The output signal from the photoelectric cell is passed
the line, for example, by the use of a vibrating photo
to an ampli?er and an ampli?ed signal is obtained.
electric element, in which the following device sets itself
The steering motor previously referred to is a well
so that an equal amount of the White background is viewed
30 known type of two-phase servo motor in which the ?eld
on either side of the line image.
is supplied from the supply mains through a reactor
In order that the cotnrol mechanism for the machine
which produces a 90° phase displacement. If a voltage
may be properly directed the portion of the line pro
which is in phase with the mains supply is applied to
jected on to or scanned by the photoelectric device must
the rotor of the servo motor then it runs in one direc
be in advance in relation to the control mechanism in
tion but if a voltage which is in phase opposition (i.e.
order to allow time for the following device to impose
the required turning effort on the steering mechanism,
and for the latter to respond, when a deviation is required.
The invention may be used in conjunction with line
following devices of known types and to facilitate a full
understanding of the invention a typical prior art type
will be described.
This comprises a casing containing
a vertical shaft rotatable about its axis and having a
tracer wheel mounted on a horizontal axis at its lowerv
end. The tracer wheel is driven by a motor running at
a substantially constant speed and bears upon a table
on which a drawing may be placed containing an out
line of the shape of the piece to be cut. The machine
includes a lower carriage running on a pair of horizon
tal parallel rails and an upper carriage running on a
phase displaced by 180°) with the mains frequency is
applied to the rotor then the motor runs in the opposite
direction. It will be evident that alternate impulses
supplied by the ampli?er are in phase with the mains
supply while the intervening impulses are in phase op
position with the mains supply. If the outline is in the
centre of the transverse scanning line of the photoelec
tric cell the impulses are of equal magnitude and if the
ampli?er output is applied to the rotor of the steering
motor the steering motor will receive a series of impulses,
alternate ones of which tend to make it run in one direc
tion and the intervening ones of which tend to make it
run in the other direction. Since its inertia, and the in
ertia of the apparatus coupled to it, is far too great to
second pair of horizontal parallel rails placed at right 50 allow the parts to respond to impulses at a frequency
angles to the ?rst pair of rails. The upper carriage may
move in all directions in a horizontal plane and the afore—
mentioned casing, as well as a ?ame-cutting torch, are
attached to it. Mounted on the upper carriage adjacent
of 120 c./s., the motor remains stationary. This is the
condition which obtains when the outline is a straight
line and the scanning line of the photoelectric cell is
truly transverse thereto. Under these conditions the
tracer wheel is parallel to the ‘outline and is rotating at
a steady speed so that the upper carriage is being carried
forward along a path which is parallel to the outline.
If the outline deviates then the photoelectric cell at
the casing, or within the casing itself, is a photoelectric
tracing device so ararnged that it “looks” downward at
the drawing on the tracing table. The photoelectric
tracer is capable of being rotated about a vertical axis
once “sees” more light on one side of the outline than
parallel to the vertical axis of the shaft carrying the
tracer wheel. This device and the shaft carrying the 60 on the other, so that the impulses supplied to the ampli
tracer wheel are coupled together so that they rotate
?er become alternately larger and smaller and the am
in synchronism and they are adapted to be rotated in
pli?er faithfully reproduces these signals. The condi
tion now is that the motor still receives alternate impulses
either direction by a steering motor which will be more
particularly described later.
65 tending to drive it in one direction and intervening im
The tracing device is provided with a vibratory spring
pulses which tend to drive it in the other direction, but
arm which carries a photoelectric cell. A lamphouse
the impulses tending to drive it in one of the directions
containing a lamp and lens projects a beam of light down
have become larger while the others have become smaller,
wardly on to the table, so that a small circular area is
brightly illuminated. The machine is adjusted so that
the outline to be traced lies within this circle, the photo
electric cell is vibrated on a line transverse to the direc
so that the steering motor begins to rotate in the one
direction. The mechanism is so arranged that the steer
ing motor rotates both the shaft carrying the tracer wheel
and the photoelectric device in such a direction as to
3,063,698
3
4
steer the upper carriage in the direction in which the
FIGURE 6 is a circuit diagram showing the connections
outline has deviated.
to the electro-magnetic actuator of FIGURES 4 and 5;
In order to give the steering device time to respond
FIGURE 7 is a diagram showing the action of the
to deviations in the outline it is arranged that the photo
device of FIGURES 2 and 3;
electric tracer device is so mounted that it is scanning
FIGURE 8 is an elevation of a following device simi
a portion of the outline in advance of the axis of the
lar to that of FIGURE 2 showing another application
scanning device. This may be achieved either by mount
of the invention;
ing the vibrating photoelectric cell arm off centre with
FIGURE 9 is a plan view of the device of FIGURE 9;
respect to the axis about which the device rotates, so that
FIGURE 10 is a diagram showing the operation of
it swings in an arc, or by mounting it centrally but at an 1O the device of FIGURES 8 and 9;
angle to the vertical so that it “looks” ahead.
FIGURE 11 is an elevation of a following device show
In order to improve the operation of the line follower
ing a further application of the invention;
it is common practice to include a small generator of the
FIGURE 12 is a plan view of the device of FIGURE
type known variously as an induction generator, a rate
11; and
generator or a tacho-generator, which produces a volt
FIGURE 13 is a diagram of the operation of the device
age which varies strictly in accordance with its speed,
of FIGURES 11 and 12.
i.e. it, produces a velocity signal. This is mechanically
Referring to FIGURE 1, a ?ame cutting machine
coupled to the steering motor and electrically connected
suitable for use with the invention comprises a frame
in the circuitry in such a way as to oppose the signals
work 11 provided with a pair of rails 12. A lower car
from the photoelectric cell. The velocity signal stabilizes t riage 13 is provided with pairs of wheels 14 on each
the operation of the steering motor and prevents over
side by which it may run along the length of the rails
shooting. The type of servo motor described and the
12. The movement of the lower carriage 13 is thus nor
use of the tacho-generator are so well known in ordinary
mal to the plane of the drawing of FIGURE 1. The
servo practice that no further description is deemed
lower carriage 13 is provided on its upper surface with
necessary.
a further pair of rails 15 set transversely of the rails
It will be obvious that, as the portion of the outline
12. An upper carriage 16 has wheels 17 adapted to
being viewed or scanned is in advance of the control
run on the rails 15. Thus, the upper carriage 16 is mov
mechanism, that is, the point of contact between the
able in any‘ direction in a plane parallel to the ground
tracer wheel and the ?xed portion of the wheel which
plane on which the frame 11 stands. A support 18
it engages, errors will occur on curves which are related
in magnitude to the degree of curvature and are a maxi
mum at sharp corners, since the following device will
cause movement of the steering motor before the trac
ing wheel has reached the point at which it should be
steered. When negotiating a right-angled sharp corner
the follower mechanism will produce a rounded corner,
the radius of the rounded corner depending upon the
amount of lead and the characteristics of the mechanism.
On the other hand, if the amount of lead is reduced be
low a certain point, instability in steering is likely to
1
mounted on the upper carriage 16 carries a rotatable
photoelectric following device 19, including a photo
electric cell 19a, which may be of a known kind; it may,
for example, consist of an arrangement in which an
image of a part of the thickness of a thick line is pro
jected on to the photoelectric cell from which the signal
falls below a mean level if the amount of light falling
on it is below a predetermined level and from which the
signal rises about the mean level if the light projected
‘ Another object is to provide a method of following
on to it is above this level. These charges are caused
to operate steering mechanism so that the device will
always tend to keep itself in such a position that the spot
projected on to it consists of a semi-circle of the dark
outline and a semi-circle of the white background. Al
ternatively it may consist of a vibratory mechanism in
which either the spot of light used for scanning, or the
an outline which includes deriving a signal dependent
photoelectric element itself, is vibrated, two signals be
upon the rate at which the outline deviates from the in
ing delivered, one corresponding to the amount of light
stantaneous direction of the following device, the signal
being used to reduce the lead of the following device.
seen on one side of the outline and the other correspond
ing to the amount of light seen on the other side of the
> A further object of the invention is to provide a fol
outline, the steering mechanism being operated in such
develop.
One object of the invention is to provide a method of
following an outline in an oxygen jet cutting machine
which is highly efficient and accurate.
lowing device for an oxygen jet cutting machine which 50 a manner as always to maintain a balance between the
will provide a high degree of accuracy of following on
two signals. Assuming ‘that the follower is of the type
curves.
in which the photoelectric cell 19a is vibrated, then it will
Still another object is to provide a following device
be attached to an arm which is coupled to a vibrator.
for an oxygen jet cutting machine in which the portion
The area of the table below the follower 19 is brightly
of the outline being viewed or scanned is normally in
illuminated, for example, by a spot light (not shown)
advance of the relative position of the control mechanism
and an image of a part of the outline is projected up
and the amount of the advance or lead is reduced ac
cording to the rate of deviation of the outline from the
instantaneous direction of the following device.
wards by a lens 31 on to the photoelectric cell. Due to
the vibration of the cell it alternately “looks” at one side
and the other side of the image. If the image is at the
Further objects and advantages of the invention will 60 centre of the vibratory path of the cell then the cell out
appear from the description thereof which follows.
put rises to the same point above a set reference level
To promote a full understanding of the invention
when looking on each side of the image. If, however,
selected embodiments thereof will now be described by
way of non-limiting examples. In the drawings:
FIGURE 1 is a diagrammatic representation of an
oxygen jet ?ame cutting machine of a known kind show
ing a photoelectric outline following device;
FIGURE 2 is an elevation of one form of following
device showing the application of the invention;
the image is not central then the cell output rises to a
higher level on one side of the image than on the other.
The alternate signals are compared and as soon as one
of them rises above the level of the other a dilference
signal is generated and is used to control an ampli?er
which causes the steering motor to run in one direction
70 or the other, in dependence upon the sense of the signal.
FIGURE 3 is a plan view of the device of FIGURE 2;
The framework 11 includes a tracing table 20 lying in a
FIGURE 4 is a sectional elevation of an electro-mag
horizontal plane and the surface thereof is frictionally
netic actuator used in the device of FIGURES 2 and 3;
engaged by tracer wheel 21 which is driven at a set speed
FIGURE 5 is a cross-sectional elevation of the actuator
through appropriate gearing by a motor contained in a
of FIGURE 4;
75 rotatable housing 22. The rotatable following device 19
3,063,698
5
and the rotatable housing 22 are coupled together by
means of a chain 23 engaged in sprockets respectively
on the device 19 and the housing 22. The steering motor
24 rotates the device 19 and the housing 22 synchro
nously through the chain drive. A rate generator or
6
ing a maximum on a sharp corner, as the following de
vice will cause a movement of the steering motor before
the tracing wheel has reached the point where turning
should have taken place. This error is eliminated or re
duced by the following device according to the invention.
tacho-generator driven ‘by the steering motor generates
When, in the known device, a. straight line is being
a signal which is connected in circuit to oppose the sig
followed no deviation signal is produced by the follow
nal from the ampli?er.
ing device. Assuming now that the following device
The arrangement so far described is known. Accord
reaches the junction of two straight lines which form an
ing to a further feature which has been proposed allow 10 obtuse angle then, as the junction is reached, a signal is
ance is made for the kerf or the width of the cut made
produced which rises rapidly as the photoelectric device
by the oxygen jet cutter, by means of an optical de
moves over the junction. The signal causes the steer
viator 25. It will be appreciated that if the photoelectric
ing motor to run in the appropriate direction to steer
tracing device follows the outline in the normal way then
the follower on to the new line and as steering progresses
the flame cutter will follow a path which corresponds
with the outline but since the cut made by the ?ame cut
ter has a de?nite width the object ?nally cut from the
plate will be slightly smaller than the outline all around
its periphery. This may be overcome by making the
the deviation signal dies away to zero.
If, on the other
hand, the follower is following a straight line which runs
into a curve which is a part of a circle then a deviation
signal is generated and the motor begins to run as be
fore, but the signal does not dies away and, in fact, re
original outline slightly larger in all directions but the 20 mains at a constant level, representing a constant rate
dii?culties involved are avoided by using the optical de
of deviation, so that the motor will continue to run at
viator.
This consists of a block of glass which is ar
ranged to de?ect the image received by the photocell
in a direction transverse to the line of movement.
By
a steady speed to provide a steady steering movement
around the curve. It will, however, always lag slightly,
as explained above.
Thus, due to the restoring action
suitable adjustment of the angle of tilt of the deviator
of the steering mechanism, which is continually endeav
allowance may be made for the kerf or, if desired, the
object cut from the plate may be made larger or smaller
than the outline.
Fixed to the upper ‘carriage 16 is a bar 26 which is
ouring to reduce the deviation to zero, the deviation sig
nal becomes effectively dependent upon the rate of de
viation.
In applying the invention a signal is required which is
dependent upon the rate of deviation of the outline from
the instantaneous direction of the device 19. When, in
the known arrangement, the device 19 is following a
provided at its end with a supporting arm 27 for an oxy
gen jet cutting burner 28. Supporting members 29‘ are
provided at the side of the framework 11 to support a
sheet of material 30 from which an object is to be out.
In operation the tracer wheel 21 is rotated at a pre
determined speed and causes the upper carriage 16 to
move in a direction lying along the plane of the tracer
wheel 21. At the same time an image of a part of the
outline is projected through a lens 31 and the deviator
25 to the following device 19. If the portion of the out
line being followed is a straight line and the plane of
the tracer wheel 21 is parallel with this line then the
tracer wheel will continue to move in that direction,
pulling the carriage 16, the cutter 28 and the device 19
with it. If, however, the outline deviates from the straight
path then the deviation causes the following device 19
to provide the appropriate signal through the ampli?er
to the steering motor 24 to rotate the device 19 about
its axis in such a manner that it tends to continue to
follow the deviating outline. Rotation of the device 19
simultaneously rotates the housing 22, thus steering the
tracer wheel 21. The tracer wheel 21 alters the direction
of movement of the upper carriage 16, and enables the
device 19 to continue to follow the outline. The change
in the direction of the upper carriage 16 causes a cor
responding change in the direction of movement of the
cutting head 28, so that the cutting head 28 eventually
cuts a shape corresponding to the shape of the outline.
straight line it provides no signal at all but as soon as
the outline deviates the device 19 provides a signal which
is dependent upon the rate of deviation. The speed of
the steering motor 24 is substantially proportional to the
signal from the device 19. A more powerful signal, also
dependent upon the rate of deviation may be obtained
from a tacho-generator coupled to the steering motor 24.
A tacho-generator is also known as an induction generator
or a rate generator. As has already been pointed out,
the error in following increases as the sharpness of the
curve increases and is a maximum when a sharp corner
is reached.
According to the invention the signal de
pendent upon the rate of deviation is used to reduce the
lead of the device 19 over the control mechanism, i.e.
the tracer wheel, and meanswill now be described for
achieving this objective.
FIGURES 2’ and 3 show the optical system of a follow
ing device comprising a housing 36 which is provided at
its upper end with an element 37, which could be a sta
tionary photoelectric cell, or an oscillating photoelectric
cell, or a light source, according to the particular photo
electric system which is employed. The lower part of
the housing 36 is provided with a pair of trunnions 38
and a casing 39 is supported on a shaft 40 and a stub
shaft 41 in the trunnions 38, the common axis of the
In order to allow time for a deviation of the outline
shaft and stub-shaft being indicated at 57. The casing
detected by the tracer head to operate the steering mecha
39 is adapted to rotate to a limited extent about the axis
nism and to change direction of movement of the upper 60 57. Near its upper end the casing 39 contains a glass
carriage 16 it must be arranged that the portion of the
cylinder 42 which is rotatable about an axis 43 spaced
outline being viewed or scanned by the device 19 is
from, and at right-angles to, the axis 57. At its lower
slightly in the lead in relation to the position of the
end the casing 39 contains a lens 45 which projects an
tracer wheel 21 which constitutes the control mecha
image of a portion of the outline 46 upwardly and on to
nism. Thus, at any moment, the point on the outline 65 the glass cylinder 42. As shown, the direction of move
on which the device 19 is working is slightly in front
ment of the following device is in a direction normal to
of the position of the tracer wheel 21.
the plane of the drawing. It will be evident that if the
The amount of lead must exceed a certain minimum
casing 39 is swung about the axis 57 -so that thetlens 45
or it is found that instability in steering occurs. Apart
moves in the direction in which the following device as
from the feature previously referred to, the jet cutting 70 a whole is moving, the portion of the line 45 which is
machine, the method of operation and the technical con
projected will be in advance of the portion of the line
siderations so far described are known in the art. It will
lying under the axis of the housing 36. In other words,
be evident that, due to the lead, an error will develop
the following device will lead the control mechanism.
when a curve is being followed, the magnitude of the
The shaft 40 has a skew gear 47 attached to its outer
error increasing as the curve becomes sharper and reach
end and this risrengaged by another skew ‘gear- 48 on'dthle
success
S
“I
swung forward with respect to‘the vertical axis 59 to
the extent indicated by the dimension 60. When a curve
actuator comprising a stator 51. The electric-magnetic
is reached the rotation of the rotor 50 under the in?uence
actuator is carried on an arm 6i; it is illustrated in more
of the signal from the tacho-generator causes the casing
detail in FIGURES 4 and 5. Referring to those ?gures,
the electro-magnetic device comprises the stator 51 which CH 39 to swing backwards so that the axis 58 begins to
approach the axis 59 and the dimension 60 is reduced or
carries a suitable winding adapted, when energized with
eliminated.
direct current, to set up a ?eld across its diameter passing
The glass cylinder 42 when in its normal position as
through the axis of the shaft 49. The rotor 50 may be
shown in FIGURES 2 and 3, will allow the image of
of soft iron and may have a winding but is preferably
a permanent magnet with its poles atitwo diametrically 10 the line 45 to pass directly upwards through it to the
element 37. It may, however, be swung in one direction
opposite points,v as indicated by the latters “N” and “S”
or the other on the axis 43 by means of a graduated
in FIGURE 4. At the end of the shaft 49 remote from
knob 62. After it is moved from its central position it
the gear 48 a spring 52 has one end anchored to the
causes the image of the line 46 to be displaced to one
shaft 49 and its other end anchored at 53 to the stator 51.
side or the other so that the following device will then
The spring 52 is wound up to a predetermined tension
end of a shaft 49 of the rotor 5b of an electro-magnetic'
and is prevented from unwinding by a bar 56 engaging
run on one side or the other of the line 45. This enables
one of two stop screws 54 and 55. The ?eld set up by
the winding of the stator 51 is normally out of line with
the ?eld of the permanent magnet of the rotor 50, so
allowance to be made for the kerf or, if desired, enables
the piece cut from the workpiece to be made larger or
smaller than the outline. The adjustment of the knob 62
related to the amount of curvature of the outline which
the line on which the tracer mechanism itself moves.
has been encountered. FIGURE 6 shows the connections
of the tacho-generator to the electro-magnetic actuator.‘
The tacho-generator ?eld 70 is excited by a constant DC.
As shown in FIGURE 10 the lead, indicated by the
dimension 60, is now equal to the amount by which the
casing 39 is moved forward with respect to the vertical
voltage and its armature 71 is connected across a poten
axis 59.
that if the winding 51 is energized with direct current 20 is quite independent of the operation of the lead adjust
ing device previously described.
flowing in the appropriate direction a turning moment is
FIGURES 8, 9 and 10 show an alternative arrange
exerted on the rotor 50 as its magnetic poles endeavor to
ment. In these ?gures elements corresponding with ele
line themselves up with the ?eld set up by the stator
ments shown in FIGURES 2, 3 and 7 have been given
winding. This causes the rotor to turn so that the bar 56
like reference numbers. The casing 39, instead of being
moves away from the stop screw against which it has
mounted on the shaft 4% and stub shaft 41 to enable it
been resting and moves towards the other stop screw.
to swing, is now provided with lugs 63 and 64 projecting
Rotation of the rotor 50 rotates the shaft 40 through the
from opposite sides, the lugs being bored so that they
gears 48 and 47 and thus swings the casing 39 about the
may slide on two bars respectively 65 and 66 inside the
axis 57. The mechanism is so arranged that the spring
housing 36. The electro-magnetic device comprising the
52 normally holds the bar 56 against the stop screw 54
rotor 50 and the stator 51 is of similar construction but
and this swings the casing 39 in the direction to give the
is now mounted with its axis horizontal and has a toothed
maximum lead. While the tracer mechanism is follow
pinion 67 mounted on the end of its shaft 49. The pinion
ing a straight line the steering motor is stationary and the
67 engages a rack 68 attached to the casing 39. Thus,
maximum lead is maintained. As soon as the outline
the casing 39, instead of being swung to and fro about an
begins to deviate slightly the steering motor begins to
axis, is now bodily moved forwards or backwards along
run and the ‘nacho-generator generates a voltage which is
tiometer 72. A part of the armature voltage is tapped
olf by the slider 73 and is applied to the winding 74 of
the stator 51 and the ?eld set up thereby acts upon the
magnetic rotor 50. The voltage applied to the windings
of the stator 51 causes some rotation of the rotor 50
against the tension of the spring 52. As the result the
casing 39 is swung back to some extent, to reduce the
amount of lead. If the deviation of the outline increases
the output of the tacho-generator increases and the rotor
50 experiences a more powerful torque, so that it turns
a little further against the tension of the spring 52, thus
further reducing the lead. If the outline contains a very
sharp curve or a corner then the steering motor increases
its speed up to a maximum, thus giving a maximum out
put voltage from the tacho-generator and maximum
'
FIGURES 11, 12 and 13 show a further method of
carrying the invention into effect. In this embodiment
the housing 36 is not required and the casing 39, of larger
diameter, is ?xed. The glass cylinder 42 is carried in
gimbals so that it may be swung about two axes mutually
at right angles, and at right-angles to the vertical axis
59. The electro-magnetic device comprising the rotor 50
and stator 51 is mounted with its axis vertical as in
FIGURE 2 and has a gear 48 secured to its shaft 49
engaging a gear 47 as before. The gear 47 is carried on
a shaft 69 which carries a frame in which the glass cylin
der 42 is supported. As shown in FIGURE 13 the lead
is now given ‘by swinging the glass cylinder 42 about the
axis 7!) of the shaft 69 and the amount by which it is
swung forward gives a lead, indicated by the dimension
60. To provide’ for the lateral displacement to allow for
kerf, or enlargement or reduction of the size of the cut
torque on the rotor 50, which is rotated through the maxi
mum angle permitted by the stop screw 55. It is ar
piece with respect to the outline, the glass cylinder 42 is
ranged that under this condition the casing 39 is swung
rotated by means of the knob 62 about the axis 43 as in
into, or almost into, a vertical position so that the lead is 60
FIGURES 2 and 8. In the last embodiment the caisng
reduced to a very small amount or to zero. As soon as
is stationary and the glass cylinder 42 is given a com
> the tracer mechanism has negotiated the sharp curve or
pound movement composed of a variable swing about the
corner the curvature of the outline is either reduced or
first axis 70 to provide a variable lead and a presettable
changed to a straight line. The speed of the steering
swing about the second axis 43 at right-angles thereto
motor is then reduced either to an intermediate speed or
to provide for kerf adjustment.
to zero and the output of the tacho-generator follows.
I claim:
The spring 52 now overcomes the torque of the rotor 50
1. In an oxygen jet cutting machine containing a photo
and moves it either partly or wholly back to the stop
electric following device which leads a control mecha
screw 54 so that the lead of the following device is either 70 nism, means to derive a signal dependent upon the amount
partly or wholly re-established.
by which an outline ‘being followed deviates from the
FIGURE 7 shows diagrammatically the operation of
the arrangement shown in FIGURES 2 and 3. When
the casing is swung about the axis 57 under the in?uence
instantaneous direction of said following device, and
electric-magnetic means responsive to said signal for auto
matically reducing the amount of lead of said following
of the spring 52 the axis of the optical system 58 is
device in accordance with the amount of deviation.
3,063,698
10
2. An arrangement as ‘claimed in claim 1 comprising a
steering motor adapted to change the path of said follow
ing device, and a tacho-generator driven by said steering
the speed of said steering motor, an optical system asso
ciated with said following device and having a lead with
respect thereto, and means to move at least a part of said
motor to generate said signal in dependence upon the
optical system in response to the said signals for auto
speed of said steering motor.
5 matically reducing the lead of said following device in
3. An arrangement as claimed in claim 1 comprising
dependence upon the speed of said motor.
an electro-magnetic actuator including a wound stator to
6. A machine as claimed in claim 5 comprising an
electro-magneti‘c actuator including a wound stator fed
with said signal, a magnetic rotor acted upon by the
reduce the amount of lead, and a spring to unge said rotor 10 ?eld of said stator adapted to turn about its axis to move
to the position of maximum lead, said rotor rotating in
at least a part of said optical system, and a spring to urge
respense to said signal against the tension of said spring.
said rotor to the position of maximum lead, said rotor
4. An arrangement as claimed in claim 1 comprising
rotating in response to said signal against the tension of
an optical system including an optical deviator associated
said spring to reduce said lead.
with said following device, said optical deviator being 15
7. A machine as claimed in claim 6 wherein said opti
which said signal is applied, a magnetic rotor acted upon
by the stator ?eld and adapted to turn about its axis to
movable about a ?rst axis transverse to the line of travel
cal system includes an optical deviator, said optical
of said following device in response to said signal to
reduce said lead, and being also adjustable about a sec
deviator is movable about a ?rst aXis transverse to the
line of travel of said following device in response to said
ond axis at right-angles to said ?rst axis to cause trans
signal to reduce said lead, and is also adjustable about a
second axis at right~angles to said ?rst axis to cause
transverse displacement of the image transmitted to said
verse displacement of the image transmitted to said fol
lowing device.
»
5. An oxygen jet cutting machine comprising a car
following device.
riage movable in all directions in a horizontal plane, an
oxygen jet cutter on said carriage movable therewith, a
References Cited in the ?le of this patent
horizontal plane support for an outline, a photoelectric 25
UNITED STATES PATENTS
following device on said ‘carriage adapted to produce
steering signals, a power driven steerable tracer wheel
2,261,644
Cockrell _____________ __ Nov. 4,
engaging the surface of said support and adapted to move
2,419,641
Hart ________________ _._. Apr. 29,
said carriage, a steering motor to steer said tracer wheel
2,499,178
Berry et al. __________ __ Feb. 28,
in response to said steering signals, generator means 30 2,851,643
Limberger ____________ __ Sept. 9,
driven by said motor to generate a signal dependent upon
2,868,993
Henry ______________ __ Jan. 13,
1941
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1958
1959
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