 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention relates to a tracer unit particularly suitable for
use with measuring machines, comprising a plurality of tracer tools which
generate an electric output signal for signalling a position of contact of
the tracer tool with a workpiece, said position being signalled, in
accordance with the type of tracer tool, either when the tracer tool
leaves the position of equilibrium or when it passes through a position of
equilibrium.
There are known individual tracer tools, both omnidirectional and
bidimensional or unidimensional, i.e., in which the tip of the tracer tool
is movable along three, or two, or one axis. For example, the tracer tools
described in U.S. Pat. No. 4,023,045 of the same Applicant are electronic
omnidirectional tracers of the type in which en electric signal is
generated when the tracer leaves the position of equilibrium. Other tracer
tools, bidimensional and unidimensional, are known for instance from the
U.S. Pat. No. 3,727,119 and from the British patent specification No.
855,676.
When carrying out measurings on outer surfaces or in inner regions where it
is possible for the whole column of the machine to be penetrated along its
axis (axis z), or when utilizing bidimensional or unidimensional tracers,
it is sometimes necessary to use tracer tools whose axis is disposed in
successive stages along different directions. Therefore, it is necessary
to detach the individual tracer tool from the head of the measuring
machine and to substitute it or to dispose it in another position.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a tracer unit comprising
a plurality of tracer tools of the type mentioned hereinabove, which will
allow carrying out, quickly and in a simple way, measurings on outer
surfaces or in inner regions into which a penetration of the tracer unit
is possible, without having to substitute the individual tracer tools for
disposing them in different positions.
According to the present invention there is provided a tracer unit for use
with measuring machines, comprising: a plurality of tracer tools, each of
which is provided with a rod arranged to come into contact with a surface
to be scanned, a movable body connected to said rod, a fixed body, first
means which supply a first signal either when said movable body leaves the
position of equilibrium relative to said fixed body or when said movable
body passes through a determined position relative to said fixed body; and
second means arranged to indicate from which the various tracer tools said
first signal is originated.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention some embodiments thereof, given
by way of a non limitative examples, will now be described with reference
to the accompanying drawings, in which:
FIG. 1 is a side elevational view of a tracer unit according to the
principles of the present invention;
FIG. 2 is a top view, sectioned along line II--II, of the tracer unit shown
in FIG. 1;
FIG. 3 is a partially sectioned side elevational view of the tracer unit of
FIG. 1, with a cable for connection to a measuring machine;
FIG. 4 is a top view, sectioned along line IV--IV, of the outer body of the
tracer unit shown in FIG. 3;
FIG. 5 is a partial side elevational view, partially sectioned along line
V--V, of the tracer unit shown in FIG. 2;
FIGS. 6, 7 and 8 are, respectively, a top view of the fixed body and a
bottom and a top view of the movable body of the cutout device of each of
the individual tracer tools included in the unit shown in FIG. 1;
FIGS. 9 and 10 are, respectively, a wiring diagram of the tracer unit
according to the present invention and a wiring diagram of the cutout
device of each of the individual tracer tools included in the unit shown
in FIG. 1;
FIGS. 11 and 12 are part setioned side elevational views of parts of two
further different embodiments of the tracer unit according to the present
invention; and
FIG. 13 is a block diagram of a portion of the electric circuit of the
individual tracers included in the units shown in FIGS. 11 and 12.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to Figures from 1 to 5, the tracer unit of the present
invention comprises a container body 1 and an upper cover 2 fixed by means
of four screws 8 (FIGS. 2 and 5). Container 1 has at its bottom end a
plane surface 4 and at its upper end four chamfered plane portions 6
equispaced by 90.degree. from each other. Formed centrally on the cover 2
and extending upwards is a cylindrical tang 11 having a ground outer
surface and being provided with an inner thread, which is mechanically
connected in a well-know manner to a head of a measuring machine (not
shown). The plane bottom surface 4 and the four chamfered plane portions 6
of the body 1 have each a through hole 12 (FIG. 4), and such five holes 12
are coaxial with five recesses 13 formed inside the container 1. In a
central region of the body 1 there is fixed by means of four screws 15
(FIGS. 4 and 5) a block 14 substantially cubic in shape. Glued onto each
of, five sides of the block 14 are three posts 17 arranged in the
respective recess 13 and equispaced by 120.degree.. Connected to the lower
end of the posts 17 by means of screws 18 is a fixed block 21 (FIGS. 3 and
6) in the shape of an annular crown with a frusto-conical central through
hole 22. On the upper portion of said block 21, whose surface is rendered
insulating, there is fixed an insulating cage 23 which is provided with
three holes 24 for the passage of the posts 17 and from which there are
projecting a metal block 207 having a plane surface, a pair of metal balls
208 and three metal balls 209, according to the configuration described in
U.S. Pat. No. 4,023,045. The cage 23 carries also a printed circuit with
an input connection 212 disposed between the outer edge of the cage 23 and
one of the balls 208, a connection 213 disposed between the other ball 208
and the block 207, and three output connections 214 each of which is
disposed between one of the balls 209 and the outer edge of the cage 23.
Disposed on the fixed block 21 is a movable block 27 provided with three
outer oblique grooves 28 (FIG. 8) disposed at 120.degree., which allow the
passage of the posts 17. Fixed on the lower surface of said movable block
27, which is made to be insulating, is an insulating cage 221, from which
project a pin 218 and two balls 219 and 220, according to the
configuration already described in U.S. Pat. No. 4,023,045. This cage 221
too carries a printed circuit including a connection 222 disposed between
the balls 219 and 220. In an axial threaded hole 33 of the movable block
27 there is screwed the end of a measuring rod 35 which comes out from the
container body 1. Bearing in the upper zone of the movable block 27 is a
cylindrical spring 37 whose other end bears against an adjusting screw 38
which is disposed in a threaded seating 41 formed in the central block 14.
Between the central block 14 and the respective fixed block 21, in each of
the five recesses 13, there is disposed an annular cylindrical element 42
which carries a printed circuit whose terminals are connected to the input
connection 212 and to the three output connections 214 of the cage 23.
Cage 23 and cage 221 provide electric connections between the various
elements (balls, blocks and pin) of the blocks 21 and 27, so as to define
six switches connected in series and in parallel, which may be compared to
a unitary cutout device arranged to supply a signal at the opening of
anyone of said six switches. Referring to FIG. 10, said cutout device,
indicated generally by reference numeral 150, is formed by the input
connection 212 which arrives at the series of two switsches 160 and 161
provided by means of the two balls 208 cooperating with the pin 218.
Switch 161 is connected, through the connection 213, to a switch 162
formed by the block 207 and the ball 219. The switch 162 is in its turn
connected through the connection 222 to three switches 163 formed by the
ball 220 and one of the three balls 209 respectively. Said three switches
163 are connected, by means of connections 43, to a logic OR gate 165
which is connected to a printed circuit 44 housed in the container 1 (FIG.
4). Connected to said printed circuit 44, which forms an intermediate
connection element, are the connections 43 pertaining to the five tracer
tools housed within the five recesses 13, as well as the connection wires
from four signal lamps 45 disposed in the four chamfered plane portions 6.
Said printed circuit 44 is connected through five connection wires 46,
which pass through a central opening 47 of the cover 2, to the five lower
contacts of a double electrical plug 48. Plug 48 is fixed by means of two
pins 51 (FIG. 2) to a block 53 which is disposed inside the tang 11 and is
positioned by means of a threaded locking ring 53 screwed into the
threaded inner opening of the tang 11. Vertically screwed into the block
52 two centering pins 54 which project with two portions, one of which has
a larger cross-section and the other one has a reduced cross-section.
Insertable into the interior of the tang 11 (FIG. 3) is a connecting block
55 connected by means of a cable 56 to a union 57 which provides the
electrical connection to the measuring machine. Disposed in the lower
portion of the connecting block 55 are an electric plug 63 for connection
to the double plug 48, and two seatings 64 for lodging therein the two
centering pins 54.
The electric circuits of the tracer unit of the present invention are shown
in FIG. 9 in which there is diagrammatically shown, as unitary cutout
device, the switch 150 formed by the assembly of the six switches
constituted by balls 208, 209, 219 and 220, pin 218 and block 207, for
each of the five tracer tools forming the tracer unit of the present
invention. Reference numeral 70 indicates a supply cable having a negative
voltage, for instance of -12 volts, which arrives at a terminal of a
switch 71 pertaining to the tracer tool whose measuring rod 35 projects
from the lower plane surface 4. The other terminal of the switch 71 is
connected to input terminals of two switches 72 and 73 pertaining to two
tracer tools whose measuring rods 35 project from two orthogonal portions
6. The outputs of the switches 72 and 73 arrive at the inputs of other two
switches 74 and 75 respectively which pertain to tracer tools whose
measuring rods 35 project from portions 6 which are parallel respectively
to the portions 6 of the rods 35 of the corresponding series switch 72 or
73. The output terminals of the switches 74 and 75 are connected by
connections 76 and 77 to impedance adaptor blocks 80 and 81, through
resistore 78 in series and resistors 79 branched from a supply source
having a voltage +V, conveniently of +5 Volts. The outputs of the two
blocks 80 and 81, which are apt to supply in output a signal at logic
level, arrive at a logic adder circuit 82 of the type OR, whose output
arrives at the inputs which are respectively complementary of two memory
circuits 83 and 84, and at an output connection 86. The circuits 83 and
84, which conveniently comprise monostable multivibrators, are arranged to
be activated on mutually opposite wave fronts, do not accept successive
signals of the same type for a predetermined period of time, and are each
provided with an output connection 87 arranged to lock for a
pre-established period of time the operation of the other circuit. The
output of the circuit 83 transmits, through a connection 88, a measuring
signal to the measuring machine.
The connections of the switches 72, 74 and 73, 75 respectively are
connected to the anodes of two diodes 90 and 91 whose cathodes are
connected, through a resistor 92, to the connection 70 and, directly, to
an impedance adaptor block 93. The outputs of the adaptor blocks 80, 81
and 93 arrive at the input of a memory circuit 94 at which arrives also,
as consent signal, the output of the circuit 83; said circuit 94 supplies
the output signals to the measuring machine. The outputs of the blocks 80,
81 and 93 arrive also at the inputs of a decoder circuit 95 which receives
also the output of the OR circuit 82; circuit 95 supplies control signals
to a visualizer 96 having seven segments, which is disposed inside the
union 57 (FIG. 3). The output of the logic OR circuit 82 arrives also, as
consent signal, to a gate circuit 99, at which arrives a signal from a
generator 100 which generates square waves at low frequency, for example
of 4 Hz. Originating from circuit 99 is an output connection 101 which
feeds the four signal lamps which are connected to the connection 70. The
circuit shown in FIG. 9 is included in two dashed portions 103 and 104
respectively, the first of which is disposed inside the container 1 and on
the printed circuit 44, whilst the second is disposed inside the union 57.
The connections between said portions 103 and 104 is obtained by means of
five connection wires formed by the wires 46, the five contact plugs 48
and 63 and the cable 56 (FIG. 3).
The operation of the tracer unit described hereinabove, provided by the
present invention, is as follows.
When the ends of each of the five measuring rods 35 are not in contact with
the surfaces to be scanned, they are disposed in the position of
equilibrium determined by the movable block 27 being pressed against the
fixed block 21, under the action of the spring 37; namely, the ball 220
bears on the three balls 209, the pin 218 bears on the two balls 208, and
the ball 219 bears on the plane block 207. When the end of one of the
measuring rods 35 meets the surface which has to be scanned, it inclines
and/or lifts the movable block 27 and therefore at least one of the
switches 160, 161, 162 and 163 shown in FIG. 10 is opened, so that the
switching assembly 150 of the tracer tool results in being open in its
generality and a signal of a different type, for instance of the type "1",
is obtained at the output of the OR gate 165. Whatever tracer tools
results in being involved in the measuring stage, and accordingly whatever
switch 71, 72, 73, 74 or 75 opens, the potential of one of the connections
76 and 77, or of both of them, changes and a different signal, for example
a signal of the type "1", is obtained at the output of the block 80 or 81
or of both of them. Accordingly, a signal of the type "1" is obtained at
the output of the OR circuit 82 and consequently circuit 83 is activated,
which circuit sends the measuring signal, along the connection 88, to the
measuring machine and locks the circuit 84 for a convenient period of
time, for example of 0.1 seconds, through the connection 87. Through the
connection 86 there is obtained also the transmission of a signal to the
machine, which signal informs about the open condition of any switch
pertaining to one of the tracer tools. The signal of the type "1" at the
output of the circuit 82 drives the circuit 99, allows the feeding of the
low frequency signal from generator 100 to the four signal lamps 45 which
are periodically lighted and extinguished so as to be visible by an
operator in practically position of the tracer unit, in order to signal
such open condition of the individual tool.
However, it is also necessary to send to the measuring machine an
information about which of the five switches 71, 72, 73, 74, 75 pertaining
to the five tracer tools is open. Such information is transmitted through
the outputs of the blocks 80, 81 and 93 whose output logic level
combination changes as a function of the switch which has been opened. In
fact, the opening of the switch 71 causes a change of the level at the
output of the blocks 80 and 81. The opening of the switches 72 or 74
causes a change of the level at the output of the block 80, whilst the
opening of the switch 73 or 75 causes a change of the level at the output
of the block 81. The identification of the opening of the switch 72 or 74,
as well as the identification of the opening of the switch 73 or 75 takes
place on the basis of the variation of logic level of the signal at the
output of the block 93. Therefore, the combination of the signals at logic
levels "0" and "1" at the output of the blocks 80, 81 and 93, which
identifies as a number in binary form the tool which has moved away from
the position of equilibrium, and which is present at the inputs of the
memory circuit 94, is memorized, by means of the consent of the of the
signal taken from the output of the circuit 83 and present, as explained
above, when any one of the switches 71, 72, 73, 74 or 75 opens. Therefore,
at the outputs of the circuit 94 there becomes present the number in
binary form which identifies the tool which has moved away from the
position of equilibrium, and this information, which is supplied to the
machine, will be utilized by the machine itself at the right moment. The
combination of the signals at logic levels at the outputs of the blocks
80, 81 and 93, which identifies the operated tool as a number in binary
form, are decoded by the decoder circuit 95, under the consent signal of
the type "1" at the output of the circuit 82, for driving the inputs of
the visualizer 96 of the "7 segments type", which therefore gives the
indication of a digit in decimal form corresponding to the number of the
tool which has moved from the position of equilibrium, and such indication
is visible to the operator, on the union 58. Therefore, when one of the
tools moves away from the position of equilibrium, there is a general
indication of this condition, in the form of a signal present on the
connection 86 and sent to the machine, and in a visible form through the
periodic lighting and extinguishing of all the lamps 45, and moreover
there is an indication of which of the various tools has been moved, in
the form of a signal combination present at the output of the circuit 94
and available to the machine, and in a visible form through the indication
of a corresponding digit in decimal form on the visualizer 96.
Successively, when the tracer tool returns to the position of equilibrium,
under the action of the spring 37, the switching assembly closes and
cosequently a signal of the type "0" is obtained at the output of the
circuit 82. Thus, circuit 84 is activated and locks the operation of the
circuit 83 for a period of time of, for example, 0.1 seconds. In such
condition of stable equilibrium there occurs also the transmission to the
machine, along the output connection 86, of the signal informing about the
condition of closure of the switches, and such signal of type "0", at the
output of the circuit 82, by controlling the gate block 99 cuts off the
supply to the signal lamps 45, which thus are extinguished again. In this
way, whilst in the memory circuit 94 there remains memorized, as long as
no new condition of opening of a switch arises again, the combination of
signals at logic levels which identifies as a number in binary form the
tool which has moved away from the position of equilibrium in fact no new
consent signal arrives from the output of the circuit 83 to store in the
circuit 94 the new input signals, the signal at the logic level "0" from
the circuit 82 blocks the decoder circuit 95 which therefore does not
supply the visualizer 96. Since the visualizer 96 gives no indication, it
indicates that all the switches are closed.
The tracer unit according to the present invention, instead of being
provided with three dimensional tracer tools, may be provided with
unidimensional tracer tools, as shown in FIG. 11, or with bidimensional
tracer tools, as shown in FIG. 12. In fact, the tracer unit shown in FIG.
11 has five unidimensional tracer tools 300, each of which is housed in
the corresponding recess 13 inside the container 1. Each of said tracers
300 is provided with a cylindrical rod 301, to which there is connected a
measuring tip 314 and on which there is inserted a cylindrical core 302
made of a magnetic material, for example soft iron. The rod 301 slides in
two bushings 303 and 304, the first of which pertains to a hollow
cylindrical body 305, whilst the second pertains to a hollow cylindrical
body 306. The upper section of the body 306 is threaded and connected to
the central block 14, whilst the body 305, which is disposed coaxially
with the body 306 and outside of it, has an upper section 307 which is
disposed around the lower end of body 306 and is fixed to the latter.
Fixed to the upper end of the rod 301 is a cup 308 which abutting against
the inner base surface of body 306 limits the external range of movement
of the rod 301 and also serves as a support for a cylindrical spring 309,
disposed inside body 306, which spring on the other side bears against a
cap 310 fixed to the body 306. Disposed inside the body 305, coaxially
with respect to the rod 301, is a cylindrical support 311 for a series of
windings of a differential transformer (not shown), which windings are
connected by connections wires 312 to the printed circuit 44. The
differential transformer and the corresponding electric circuit of the
tracer tool in FIG. 11, are represented in FIG. 13 in which an oscillator
320 having a high frequency, for example of 50 KHz, feeds a primary
winding 321 of said differential transformer 322 which is disposed inside
the cylindrical support 311. The differential transformer 322 has two
secondary windings 323 which have one end connected together and the other
end connected to the ends of a potentiometer 324. The common end of the
secondary windings 323 and one end of the primary winding 321 are
connected to earth. The slider of the potentiometer 324 is connected to
the inverting input of a differential amplifier 325 which provides a
threshold comparator with hysteresis, whose output arrives at an input 326
of a demodulator 327 which may conveniently be a bistable multivibrator.
Oscillator 320 supplies also a generator 328 which generates clock signals
and whose output is connected to another input 329 of the demodulator 327.
The output of demodulator 327 is connected to a control input 330 of a
block 331 which is provided with two outer terminals 332 and 333 and whose
operation may be compared with that of a switch. Said block may for
example comprise a field effect transistor.
The operation of the tracer unit of FIG. 11, with reference to the diagram
of FIG. 13, is as follows. In rest conditions, when the ends of the five
measuring tips 314 are not in contact with the surface which has to be
scanned, because of the action of the spring 309 the rod 301 is in the
position shown in the Figure, having a greater external extension, and the
core 302 gives rise within the secondary windings 323 of the differential
transformer 322 to waveforms such that, when taken from the potentiometer
324 and supplied, through the differential amplifier 325, to the input 326
of the demodulator 327 where they are compared with the signals present at
the input 329 and coming from the generator 328, at the output of the
demodulator 327 there is obtained a signal of constant value which arrives
at the input 330 of the block 331 and maintains in a constant
configuration (for example, closed) the equivalent switch between the
terminals 332 and 333. When the end of one of the tips 314 meets the
surface to be scanned, the rod 301 enters again the bodies 305 and 306,
and the core 302, by passing through a position of electrical equilibrium
relative to the position of the two secondary windings 323 of the
differential transforme 322, gives rise in said secondary windings 323 to
waveforms having a changed amplitude, which are such that the signal taken
from the slider of the potentiometer 324 results in having an inverted
phase, and by means of the demodulator 327 which compares the changed
signal of the differential amplifier 325 with the always identical signal,
at frequency of 50 MHz, of the generator 328, there is obtained at the
output of the demodulator 327 a signal of different constant value which
arrives at the input 330 of the block 331 and maintains in a complementary
constant configuration (for example, open) the equivalent switch between
the terminals 332 and 333. Since the behaviour of the block 331 may be
compared to that of a switch, each block 331 pertaining to the five tracer
tools of the tracer unit may be compared to one of the five switches 71,
72, 73, 74 and 75 of the diagram of FIG. 9, which thus has an operation
identical to that described before, and there is obtained an identical
indication as to which of the five tracer tools has carried out the
scanning.
With reference to FIG. 13, all the various elements shown, except the
differential transformer 322, may conveniently be disposed on the printed
circuit 44.
The trcer unit of FIG. 12 has five bidimensional tracer tools 400, each of
which is housed in the corresponding recess 13 inside the container 1.
Each tracer tool 400 has a scanning rod 401 provided with a measuring tip
406 and connected by means of a pin 402 ot a supporting structure 403
formed by two side walls 404 connected to parts 405. Fixed to the rear end
of the rod 401 is a core 407 made of a magnetic material, for example
ferrite, whose heading surface has a contour extending along an arc of a
circle. Confronting the core 407 is an E-shaped core 408 of magnetic
material, such as ferrite, with the three arms which terminate, generally,
according to the contour of an arch of a circle concentric with that of
the core 407. On the central arm of the core 408 there is wound a primary
winding of a differential transformer, whilst on the two side arms of the
core 408 there are wound the secondary windings of the differential
transformer. Said windings are not shown, but they correspond to the
windings 321 and 323 of the differential transformer 322 shown in FIG. 13.
The core 408 is fixed to a body 410, to which there is fixed also the
upper portion of the supporting structure 403, and has also a portion 411
of circular cross-section, to which there is fixed a screw 412, and a
cylindrical portion 413 which is inserted into a double cage bearing 414.
Fixed to the upper end of the cylindrical portion 413 by means of a screw
416 is a body 417 having fixed thereto a pin 418 to which there is
connected the end of a spring 419 whose other end is connected to a pin
421 fixed to a container 422 in the shape of a hollow cylinder, which
encloses the cylindrical portion 413 and has an externally threaded upper
portion 423 which is screwed onto the central block 14. Container 422 has
at its lower portion a missing section extending along a sector of
90.degree., which limits to such value the angular movement of the screw
412.
The operation of the tracer unit shown in FIG. 12 which utilizes the same
electric diagram shown in FIG. 13, is as follows. In the rest condition,
in which the ends of the five measuring tips 406 are not in contact with
the surface to be scanned, the rod 401 is inclined and the core 407, which
is not in the position of equilibrium relative to the core 408, gives rise
in the differential transformer 322 to such waveforms that the equivalent
switch between terminals 332 and 333 of the block 331 remains in a
constant condition (for example, closed). As the end of one the tips 406
meets the surface to be scanned, the rod 401 rotates about the pivot 402
and the core 407, by passing through a position of electrical equilibrium
with respect to the core 408, gives rise in the differential transformer
322 to waveforms which are such that the equivalent switch between the
terminals 332 and 333 of the block 331 assume the complementary condition
(for example, closed). Therefore, the operation of the diagram of FIG. 9,
for the tracer unit of FIG. 12, is identical to that already described for
the tracer units of FIGS. 11 and 3. Said tracer tool 400 may carry out
scannings in two directions orthogonal to one another; in fact, when
rotating through 90.degree. the supporting structure 403, which rotation
is limited by the head of the screw 412 which abuts against the edges of
the removed section at the lower end of the body 422, the rod 401 may
rotate in a direction orthogonal to the former. The spring 419, which
results in being stretched in the two positions of the supporting
structure 403 which are orthogonal to one another, serves to maintain the
stability of said two positions.
The tracer unit of the present invention, described hereinabove, has many
advantages of being conveniently and reliably operable and of having a
relatively simple constrution. First of all it allows carrying out
scannings in different directions in a very simple way, without having to
substitute the tracer tool or to change its position, by simply utilizing
a different one of the five measuring rods.
Thus, the tracer unit of the present invention affords convenient
combinations of tracer tools of the unidimensional or bidimensional type
for obtaining performances which otherwise would be obtainable by means of
tracer tools of the three dimensional type. The indication as to which of
the five tracer tools has carried out the scanning and has therefore moved
away from the position of equilibrium or has passed through the position
of equilibrium, takes place at logic levels, and there are obtained a
memorized signal which arrives at the measuring machine when required, and
a signal which arrives at a visualizer device for the operator. The
particular mutual connection of the switching assemblies pertaining to the
five tracer tools allows having an electric connection between the tracer
unit and the union of attachment to the machine, by means of only five
connection wires, which allows a simple construction of the tracer unit.
Finally, it is obvious that modifications and variations of the embodiment
described hereinabove might be possible both in the shape and arrangement
of the various component parts, without departing from the scope of the
present invention. For example, in a single tracer unit there may also be
included single tracer tools of different types, i.e., three dimensional
and/or bidimensional and/or unidimensional tracer tools.
The tracer unit of the present invention may also include tracer tools
constructed in a different way with respect to each other; thus, it may
also include tracer tools of the type described in the U.S. Pat. No.
3,727,119 or of the type described in the British patent specification No.
855,676. Also, it may include tracer tools of a known type different from
those mentioned hereinabove, for example tracer tools in which the
detection of the contact may be achieved through variation of a capacity,
or by means of an emitter and a corresponding receiver for example of the
photoelectric type or of the laser ray type, or also in another way.
* * * * *
|
|
 |
|
 |
Description |
|
