Bidimensional tracer of machine tools or measuring machines

A bidimensional tracer for machine tools or measuring machines is described. Said tracer comprises a body for the connection to the machine, an end arranged to come into contact with a surface, and two detector elements apt to emit signals of detection of the movements of the said end, along two orthogonal directions, produced by the contact with the said surface. The main characteristic of the tracer is that said detector elements simultaneously detect the said movements along the said two directions, the said two detector elements comprising each a portion stationary relative to the said connection body and a portion movable as a function of the movements of the said end.

BACKGROUND OF THE INVENTION 
The present invention relates to a bidimensional tracer for machine tools 
or measuring machines, which comprises a body having the form of a 
cylindrical tang for connection to the machine, and a terminal bar having 
an end which is pointed or ball-shaped or simulates a tool and is intended 
to come into contact with a surface on which the operation is to be 
carried out, and further comprises means which emit detection signals of 
the movements of the said end along two orthogonal directions, which take 
place in consequence of the contact of the said end with the surface on 
which the operation is being carried out. 
The prior art bidimensional tracers do not work in a completely 
satisfactory manner, inasmuch as they either are not practical in use 
because of their inability to detect the movements of the end of the bar 
in the two orthogonal direction simultaneously or do not ensure a 
detection of such movements with the precision required for particular 
applications, which precision may reach even the level of one tenth of a 
.mu.m, or do not have a sufficiently repeatable rest position. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a bidimensional tracer 
which will not have the aforementioned disadvantages, and will therefore 
be able to be advantageously used mainly in the detection of the profiles 
of models of mechanical pieces according to detection systems of known 
type, such as for example scanning measurement or contour measurement or 
point by point measurement. 
In particular, it is an object of the present invention to provide a 
bidimensional tracer apt to be used under direct connection to the 
measuring machine or to the machine tool, i.e. a tracer which will be able 
to be connected to the end of a column movable by the movable carriages of 
the machine, generally in the three orthogonal directions, and which will 
moreover be apt to be used as an interlocking sensor of a tracer provided 
with electric motors for moving a detection bar along orthogonal 
directions (for example, of the type described in the Italian Patent 
Application No. 68681-A/77 of the same Applicant). In fact, generally such 
tracers provided with electric motors are used with machines of relatively 
large overall dimensions, i.e. machines which have a considerable inertia, 
so that it is useful to have an interlocking sensor, disposed on the said 
detection bar, to control the said motors of the tracer, so as to obtain a 
relatively reduced inertia of the system of detection of the surface which 
will allow to absorb the more rapid variations in the discontinuity of the 
surface to be scanned, so that the end of the sensor will always be 
maintained in contact with the surface to be detected. 
According to the present invention there is provided a bidimensional tracer 
for machine tools or measuring machines, comprising a body for connection 
to the said machine, an end arranged to come into contact with a surface, 
and means for emitting signals of detection of the movements of the said 
end, along two orthogonal directions, produced by the contact with the 
said surface, wherein the said means comprise two separate detecting 
elements for the simultaneous detection of the said movements along the 
said two directions, the said two detector elements comprising each a 
portion stationary relative to the said connection body and a portion 
movable as a function of the movements of the said end.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. from 1 to 7, the tracer according to the present 
invention comprises a cylindrical tang 1 which originates from a circular 
cover 2 and is provided, in its upper portion, with an electric connection 
block 3 and a recess 4 apt to receive a pin 5 fastened to a body 6 which 
is locked, by means of a dowel 7, inside a body 8. The said body 8 may be 
part of the end of a column of a measuring machine or a machine tool, 
movable by the carriages of the machine, or may be formed by the end 
portion of a detection bar projecting from the lower portion of a tracer 
provided with electric motors for moving the said bar, for example of the 
type described in the Italian Patent Application No. 68681-A/77. Disposed 
towards the lower portion of the said body 8 is a dowel 11 which 
cooperates to lock the cylindrical tang 1. Furthermore, fixed inside the 
body 6 is an electric connection block 12 which has, connected to its 
upper terminals, wires 13 for connection to the machine, whilst in its 
lower portion it is connected to block 3 having electric connection wires 
14 extending therefrom. 
Cover 2 is fixed, by means of three screws 15, to a body 16 which is 
circular in shape and provided with an external thread, so that it is 
screwed within the upper portion of an outer cylindrical housing 17 having 
a lower truncated conical section 18 provided with a central hole 19. 
Body 16 has also three holes 21 into which the stems of three screws 22 are 
screwed whose head bears against the lower surface of a circular body 23. 
The facing surfaces of the bodies 16 and 23, though being rigidly 
connected to one another by the tightened screws 22, are maintained spaced 
from one another by three cylindrical spacers 24 disposed around the three 
screws 22. 
A circular portion 25 of a body 26 is rigidly clamped on the lower surface 
of the body 23 by means of three screws 27 whose heads bear in recesses 28 
of the body 23 and whose stems are screwed into the portion 25. 
Moreover, the said portion 25 has three recesses 29 for the passage of the 
heads of the screws 22 against the body 23. 
Extending downwards from the center of the portion 25 is a cylindrical 
portion 31 which is integral with the portion 25 and from the lower end of 
which are branched three arms 32 equispaced by 120.degree.. 
Body 26, beneath the arms 32, has in its center a cylindrical hollow 
portion 33 which projects through the hole 19 and has an inner thread so 
as to allow screwing an upper section 34 of a detection bar 35 which 
carries at its end a ball 36 intended to be brought into contact with a 
surface to be scanned. 
The three arms 32 are contained in a plane perpendicular to an axis of 
symmetry 37 of the tracer, which axis coincides with the axis of the bar 
35, whilst the axis of the cylindrical portion 31 coincides with the said 
axis 37. The cross-section of the cylindrical portion 31, in the plane 
perpendicular to axis 37, is relatively reduced with respect to the total 
cross-section of the arms 32 and to the cross-section of the portion 25, 
so as to allow a repeatable movement of the assembly of arms 32 relative 
to the portion 25, thanks to the resilient deformation of the portion 31 
under the action of a movement imparted to the ball 36. 
Conveniently, the body 26 is made of a material which has the desired 
characteristics of sufficient rigidity and resilient deformability, for 
example steel. 
Bearing on the end of the three arms 32 are the heads of three screws 42, 
whose stems are screwed, in the upper portion, towards the apexes of a 
triangular body 43. The said body 43, though being rigidly coupled, is 
spaced from the three arms 32 by means of three cylindrical spacers 44 
disposed around the three screws 44 and passing through three recesses 45 
and three recesses 46 formed in the portion 25 and the body 23 
respectively. 
Body 43 has two recesses 47 and 48 formed, respectively, on the upper and 
lower surface, in which there are fixed two ferromagnetic blocks 50 and 51 
respectively, having substantially the configuration of a parallelepiped, 
which are disposed with the major axis along the one or the other of two 
orthogonal directions contained in the plane perpendicular to the axis 37, 
and form the two movable cores of two transformers arranged to detect the 
movements of the ball 36 in the said two orthogonal directions. 
Facing the lower side of the block 51 are the three ends of the stems of an 
E-shaped ferromagnetic block 52 which constitutes the fixed core of one of 
the said two transformers. 
Wound around the central stem and the two side stems of the block 52 are a 
primary winding 53 and two secondary windings 54, respectively, from which 
the electric detection signal of the movement of the ball 36 along the 
direction of the axis of block 51 is obtained. Block 52 is housed within a 
rectangular recess 55 formed in the body 23 and is fastened to this 
latter, conveniently by means of an adhesive introduced into the recess 
55. 
Facing the upper side of block 50 are the three ends of the stems of an 
E-shaped ferromagnetic block 57 which constitutes the fixed core of the 
other of the said two transformers. Wound around the central stem and the 
two side stems of block 57 are, respectively, a primary winding 58 and two 
secondary windings 59, from which the electric detection signal of the 
movement of the ball 32 along the direction of the axis of block 50 is 
obtained. Also block 57 is housed within a rectangular recess 60 formed in 
the body 16 and is fixed to this latter, conveniently by means of an 
adhesive introduced into the recess 60. 
The passage of the wires 14 serving to provide the electric connection to 
the two transformers and the elements which carry out a first processing 
of the signals coming from the transformers, which transformers pertain to 
a printed circuit 62 which is fixed to the lower region of the portion 25 
by means of a screw 63 with the interposition of a spacer 64, is obtained 
by means of a first recess 66 formed in the lower surface of the cover 2 
and in the upper surface of body 16 in a radial direction, a through hole 
67 formed in the body 16, a recess 68 formed in the lower surface of body 
16 and connected to the recess 60 for the connection to the first 
transformer, a recess 70 formed in the body 23 and connected to the recess 
55 for the connection to the second transformer, and two through holes 71 
and 72 formed in the body 23 and the portion 25 to allow the connection to 
the printed circuit 62. 
Finally, the bodies 16, 23 and 43 supporting the stationary and the movable 
portions of the two transformers are made of a non ferromagnetic material; 
conveniently, they, as well as the housing 17, are made of aluminium, in 
order to render relatively reduced the total weight of the tracer. 
The operation of the bidimensional tracer according to the present 
invention is as follows. 
Let us suppose that the body 8 constitutes the end portion of a movable 
column of a machine; therefore, tang 1 will be directly connected to the 
said machine by introducing it into the body 8, and the positioning of the 
pin 5 in the recess 4 ensures the correct connection positioning between 
the electric connection blocks 3 and 12. 
Thus, under the control imparted by the machine for the movements of the 
column, ball 36 is brought into contact with a surface which has to be 
detected, according to one of the known detection methods. Therefore, ball 
36 moves away from its position of equilibrium (with values which are in 
the order of one .mu.m) along directions contained in the plane 
perpendicular to the axis 37, and such movement is allowed by the 
cylindrical portion 31 of reduced cross-section, which allows the movement 
of the three arms 32 relative to the portion 25 which, instead, remains 
stationary relative to the axis 37, for the rigid connection to the tang 1 
by means of the screws 27, the body 23, the screws 22, the body 16 and the 
screws 15. 
The said movement is of the resilient type, so that ball 36, when it 
becomes free again, returns to its original zero position, and the maximum 
permissible value of movement, in order to avoid yielding phenomena, is 
limited by the diameter of the hole 19 of the end section 18 of the 
housing 17. 
Therefore, the said movement of the arms 32 gives rise to a corresponding 
movement of the body 43 and, consequently, the two blocks 50 and 51 which 
constitute the movable parts of the core of the two transformers. 
The movement of the blocks 50 and 51 relative to the corresponding 
stationary blocks 57 and 52 gives rise, in the said two transformers, to 
signals of detection of the movement of the ball 36 along two orthogonal 
directions contained in the plane perpendicular to the axis 37 (which 
coincide with the planes of symmetry of the said transformers). 
Thus, with the tracer according to the present invention there is obtained 
the advantage of having a simultaneous detection, along the said two 
orthogonal directions, of the movements of the end of the tracer, with 
consequent improvements and versatility of application, and moreover, 
thanks to the structure of the tracer itself, in the detection of such 
movements during the return to the rest position a very high degree of 
precision, even in the order of 1/10 of a micron, is obtained. 
The signals which are a function of the said detection values of the 
movements may then be utilized in the manner deemed to be the most 
suitable; for example, they can be sent directly to control the movements 
of the column of the machine so as to always bring the tracer towards its 
position of equilibrium, i.e. with the bar 35 in a not deflected position, 
or it is possible to set in the control computer of the machine a 
deflection value for the said bar 35 so that the column will be operated 
to move in such a manner as to make the said bar 35 assume the said 
deflection value; this is particularly useful in some stages of detection 
of a surface, in order to ensure during the scanning of the surface a 
substantially continuous contact, under a uniform pressure, of the ball 36 
on the said surface. Obviously, the said predetermined deflection value is 
variable at will and is a function of various parameters, such as the 
speed of detection, the type of detection tip, the type of surface to be 
scanned etc. 
Finally, particularly advantageous is the utilization of the tracer of the 
present invention as an interlocking sensor for a tracer provided with 
motors, as already mentioned hereinabove, in which case the said body 8 
would form the end portion of the detection bar of such a tracer provided 
with motors. 
In this case, the movement detection signals coming from the two 
transformers would conveniently be sent to control the electric motors of 
the tracer which control the corresponding movements, whilst the movements 
of the bar of the motorized tracer would control the movements of the 
column to which the said motorized tracer is connected. 
In this way, even in the case of large machines it would be possible to 
carry out detections at a relatively high speed, since there would be a 
rapid adaptation of the detection tip to the profile of the surface, 
inasmuch as the position of the said tip may be controlled in a very 
precise and rapid manner directly by the motors of the tracer. 
Of course, also in this type of application with a motorized tracer a 
deflection value may be programmed for the bar 35, in order to have a type 
of operation with a substantially continuous force of detection contact, 
as described. 
Finally, it is clear that many modifications and variations may by applied 
to the embodiment described and illustrated of the tracer according to the 
present invention, without departing from the scope of the inventive idea 
contained in the invention.