Drilling machine for boards, particularly of printed circuits

The drilling machine comprises a pair of cross slides formed of two parallelepiped blocks of granite connected as a T above a horizontally stationary board carrying table. The transverse block carries two operating heads and, by means of pneumostatic bearings, guides their movement along the X-axis. The other block is guided by the machine frame by means of other pneumostatic bearings. Each head carries a spindle operable to lock and unlock the tool to permit automatic tool replacement from a corresponding tool magazine with provision for checking the integrity of the engaged tool. One of the heads can be disengaged from the X-axis servomotor and connected to the other one at a predetermined distance. Two series of equal printed circuit supports can be drilled simultaneously by using a single package of boards to be cut after the drilling or the etching. Tool changing and tool integrity checking operations can be effected simultaneously for the two operating heads.

BACKGROUND OF THE INVENTION 
The present invention relates to a drilling machine for boards, 
particularly of printed circuits, comprising at least one drilling head, a 
board carrying table, and displacing means for relatively displacing said 
table and said head along two coordinate axes. 
Several drilling machines of the above said type are known. In them the 
table is normally mounted on a pair of slides, whereas the drilling head 
or the heads are mounted on the machine frame in a fixed position. These 
drilling machines, at each cycle are able to drill a package of a few 
boards predisposed between two dummy boards and mutually secured through 
reference pins for loading them in a predetermined position on the table. 
The boards are provided each one for a single printed circuit, whereby in 
case of a multiple drilling machine, each head can drill a corresponding 
package of boards to be individually mounted on the table. 
In the known drilling machines the package loading and unloading operation 
is normally long and difficult in the structure with stationary heads, 
where the space is limited by the heads and the table, whereby the 
drilling is costly. 
SUMMARY OF THE INVENTION 
The technical problem that the invention intends to solve consists in 
providing a drilling machine having the greatest operative flexibility and 
reliability, and wherein the working cycle can be considerably reduced. 
This technical problem is solved by the drilling machine according to the 
invention, which is characterized in that said table is stationary along 
said axes, and said head is carried by a pair of cross slides for being 
displaced to any drilling position with respect to said table. 
According to another characteristic of the invention the head is movable on 
a transverse bar parallel to one of said axes and secured as a T to a 
prismatic bar parallel to the other axis, said transverse bar being 
movable on the machine frame, said transverse and said longitudinal bars 
being formed of two granite blocks with a rectangular section, rigidly 
mutually connected and cooperating with two air bearing systems associated 
with said head and with the frame. 
These and other characteristics of the invention will become more clear 
from the following description of a preferred embodiment, made by way of 
example, but not in a limiting sense.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, the drilling machine includes a machine frame 6 
and a drill operating head 9 for a group of boards 27 of support for 
printed circuits. The boards 27 are made of epoxy-glass coated with a 
metallic layer, which will be then photoetched according to the circuit to 
be manufactured. The drilling is effected in a series of positions to 
allow the connection between circuit points on the two faces of the board 
and the insertion of the possible discrete or integrated circuits. 
The head 9 is provided with a spindle 24 which carries a drilling tool 26 
and will be better seen hereinafter. The boards 27 are located in a table 
32, which is not movable on the horizontal plane, with respect to the 
stationary machine frame 6, whereas the head 9 is movable along two 
coordinate axes conventionally indicated as X and Y (FIG. 3). 
To this end, the head 9 is carried by a pair of cross slides, generically 
indicated by 7, which enables it to be moved with respect to the table 32 
in any drilling position. These slides comprise a strong transverse bar 10 
parallel to the X-axis and secured as a T to a prismatic bar 11 parallel 
to the Y-axis. The T structure of the bar 10 and the bar 11 is located 
above the table 32, whereby the head 9 effects the drilling by acting from 
the top downwards on the boards 27 located on the table 32. In this way 
the accessibility to the operator of the table for loading and/or the 
unloading of the boards is increased. In particular, both the bar 10 and 
the bar 11 are formed of two strong granite blocks of a rectangular 
section, worked with the highest precision and rigidly mutually secured by 
means of a series of dowel screws 35 (FIG. 6). The resulting structure 7 
is thus very rigid, substantially insensible to the thermal dilatations 
and deprived of elastic flexings. 
The bar 11 (FIG. 2) is guided into a double portal structure 36, 36', which 
is part of the frame 6. The two portals are mutually similar, whereby only 
the portal 36 will be described, whereas in the portal 36' the 
corresponding parts are indicated with the same reference numbers provided 
with prime. The portal 36 comprises a pair of transverse plates 37 and 38 
having a reverse T aperture 39 (FIG. 4). Into the aperture 39 the two 
plates 37 and 38 are connected by a set of longitudinal horizontal plates 
40, 41, 42 and vertical plates 43 and 44. The two pairs of plates 37, 38 
and 37', 38' (FIG. 2) are also connected laterally by two vertical plates 
45 and upwards by a cover plate 46. 
Mounted on the portal 36 (FIG. 4) are two series of air bearings 47 and 48, 
each one adapted to guide three faces of the bar 11, and a central air 
support bearing 49. The bearings 47, 48, 49 and 47', 48', 49' (FIG. 2) 
define thus the guide for the bar 11 along the Y-axis. 
Secured to the backward end of the bar 11 (FIGS. 2 and 3) is a servomotor 
16, formed of a direct current electric motor, provided with a tachometer 
generator for the speed feed back control. The shaft 61 of the motor 16 is 
connected to an endless screw 50 by means of a front clutch 55 adapted to 
allow possible small axial displacements between the shaft 61 and the 
screw 50. This latter is rotatably mounted on two bearings 51 and 52 
carried by two corresponding supports 53 and 54 secured to the same bar 
11. The screw 50 engages a female screw 56 secured to a vertical plate 57 
in turn rigidly connected to the transverse plate 38. 
Furthermore, secured to the bar 11 (FIG. 4) is a finely graduated bar 58 
adapted to be read by a position transducer 59, formed of an optical 
prisma reader with off-set diodes, known per se. The transducer 59 is 
secured to a bracket 60 rigidly connected to the plate 57. 
The drilling head 9 comprises a carriage 21 (FIG. 6) formed of a 
C-structure, mounted on which are two other series of air bearings 62 and 
63, each one cooperating in three planes with the bar 10. Furthermore, 
secured to the upper part of the carriage 21 is a prismatic support 67 
having a cylindrical hole 68 (FIG. 5). Rotatably mounted in this hole is a 
sleeve 69, which is secured to a female screw 71 in engagement with an 
endless screw 72. This latter at the two ends is secured to two plates 15 
(FIG. 3) in turn secured to the two end faces of the bar 10. 
Furthermore, secured to the sleeve 69 (FIG. 5) is a toothed pulley 75 
connected through a toothed belt 76 to a second toothed pulley 77 having a 
diameter twice that of the pulley 75. The pulley 77 is secured to the 
shaft of a direct current electric motor 13 provided with a tachometer 
generator. The motor 13 is secured to the support 67 and forms the 
servomotor for the X-axis. Finally secured to the backward surface of the 
bar 10 is another graduated bar 79 (FIG. 6) adapted to be read by another 
optical position transducer 81 carried by a small plate 82 secured to the 
carriage 21. 
Vertically slidable on the carriage 21 along the Z-axis is a quill 22, 
which is guided by a pair of forward rollers 83 carried by a support 84 
and two pairs of lateral rollers 86, only one of which is visible in FIG. 
6, carried by two corresponding supports 87. The support 84 and the two 
supports 87 are secured to the carriage 21. 
Rotatably mounted on the quill 22 is the spindle 24, which is connected to 
the rotor of an electric motor 23 (FIG. 2), the stator of which is secured 
to the quill 22. This latters carries also a board pressing device 28, 
adapted to be operated during the drilling for keeping the boards 27 
pressed, and a device for the suction of the debris of the drilling 
machine. 
Furthermore, secured to the quill 22 is a female screw 91 (FIG. 5) 
cooperating with an endless screw 92 connected through a joint 93 to the 
shaft 94 of a third direct current electric motor 31, provided also with a 
tachometer generator and forming the servomotor for the Z-axis. The joint 
93 is mounted on a projection 96 of the carriage 21, whereas the motor 31 
is secured to a bracket 97 of the carriage 21. 
Secured to the upper end of the quill 22 is a projection 101 carrying a rod 
102, which cooperates with a linear potentiometer 103 secured to the 
carriage 21. The potentiometer 103 is thus adapted to indicate the 
position of the quill 22 along the Z-axis. 
The three servomotors 13, 16 and 31 are controlled by a numerical control 
unit 18 (FIG. 8) known per se, which receives the signals of the 
transducers 59, 81 and 103 for the position feedback and the signals of 
the tachometer generators of the same motors. 
The unit 18 is controlled by a program unit 19, for example a magnetic tape 
unit, recorded on which is the program of one or more drilling cycles. The 
unit 18 is also connected to a command keyboard 20 and to a display screen 
25 for example of the cathode ray type. The unit 18 may have provision 
also for the recording of a new program set up on the keyboard 20. 
The unit 18 is also adapted to control the motor 23 of the spindle 24, two 
electrovalves 109 and 111 for the air bearings 62, 63 of the X-axis (FIG. 
6) and 47, 48, 49 and 47', 48' and 49' of the Y-axis (FIG. 4). Finally, 
the unit 18 (FIG. 8) is adapted to control through an electrovalve 112 a 
pneumatic device for operating the spindle 24 (FIG. 6) in order to lock 
and unlock the tool 28 inserted thereinto. 
Located on a plate 113 (FIGS. 6 and 7) of the stationary machine frame 6 is 
a tool magazine, generically indicated by 114, to allow the changing of 
the tool 26 both in the case of changing of working and in the case of 
tool breakage, as well as when it is considered worn after a certain 
number of holes. The magazine 114 is formed of a support 116 secured to 
the plate 113 of the machine frame 6, and carries a set of nine tool 
seats, each one formed of a sleeve 117 secured to the support 116. 
Vertically slidable in each sleeve 117 is an elastic grip, formed of a 
bushing 118 provided upwards with vertical notches. The bushing 118 can 
engage a collar 119, which is provided on each tool 26. Each grip 118 is 
normally held in raised position by a compression spring 120, which allows 
for a certain downward stroke, in case the spindle 24 is lowered when is 
not exactly aligned with the bushing 118. 
Another sleeve 117, seen in FIG. 7 at the right end of the magazine 114, 
carries a bushing 121, mounted in a manner similar to the grips 118, but 
of a greater diameter and without the vertical notches. Secured to the 
bushing 121 is a microswitch 122 adapted to be engaged by the tip of the 
tool 26, in order to signal possible breakages of the same tool to the 
control unit 18 (FIG. 8). The nine tools 26 (FIG. 7), which may be located 
in the grips 118, may all have different diameters, or may be mutually 
equal in groups. They can be selected by the program recorded in the unit 
19 (FIG. 8) according to their position in the magazine 114. 
The board drilling machine operates as follows. 
At the beginning the head 9 is located at the zero position, dotted in FIG. 
3, and allows the loading of the package of boards 27 on the table 32. 
Operating a key of the keyboard 20 (FIG. 8), puts in operation the control 
unit 18, which at first through the electrovalves 109 and 111 commands the 
operation of the air bearings 62, 63, 47, 48, 49 and 47', 48', 49' (FIGS. 
2 and 6) of the axes X and Y. Then, in the case that the tool 26 is 
inserted into the spindle 24, a selection and gripping of the tool 26 
command is operated on the keyboard 20 (FIG. 8). 
Then the unit 18, through the servomotor 13, causes the carriage 21 (FIG. 
6) to slide with the bearings 62, 63 on the bar 10 and through the 
servomotor 16 (FIG. 2) to cause the bar 11 to slide on the bearing 47, 48, 
49 and 47', 48', 49' (FIG. 4). Then the program unit 19 (FIG. 8) controls 
the unit 18 in a manner to cause at first the positioning of the head 9 in 
correspondence with the sleeve 117 (FIG. 7) of the magazine 114, where the 
tool 26 to be selected lies. 
Then the program unit 19 (FIG. 8) controls the unit 18 in a manner to 
command the Z-axis servomotor 31 to lower the quill 22 (FIG. 2) to engage 
the selected tool 26 with the spindle 24. Now the control unit 18 operates 
the penumatic device 112 for locking the spindle 24 on tool 26, whereby by 
returning the quill 22 upwards, the tool 26 is pulled out from the grip 
118. 
Now the control unit 18 (FIG. 8) displaces the head 9 in a manner so as to 
bring it in correspondence with the bushing 121, to check whether the tool 
26 is whole. Subsequently, by operating a further command of the keyboard 
20 (FIG. 8), the control unit 18 is commanded in a manner so as to 
displace the head 9 (FIG. 3) in sequence to the positions foreseen for the 
drilling, recorded in the program unit 19, whereby the package of boards 
27 is drilled in these positions. 
Upon terminating the drilling of the package of boards 27, the head 9 is 
brought to the zero position, whereby a new drilling cycle can be started. 
The checking of the integrity of tool 26 can also be automatically 
commanded before the starting of a drilling cycle or with less frequency. 
If in one of these checkings the tool 26 (FIG. 6) fails to engage the 
microswitch 122, the control unit 18 (FIG. 8) indicates the emergency to 
the operator through the screen 25 or by means of a pilot light not shown 
in the drawings. Furthermore, the unit 18 blocks the further execution of 
the drilling program. 
Then the operator, by means of the keyboard, may select a new tool 26 and 
command a tool changing operation. In this operation the control unit 18 
first brings the head 9 over the magazine 114 (FIG. 6) in correspondence 
with the seat of the tool 26 to be replaced, then it brings the quill 22 
to insert the tool 26 into the sleeve 117 and through the penumatic device 
112 (FIG. 8) unlocks the spindle 24. Now the grip 118 engages the collar 
119 and holds the tool 26. Thereafter the control unit 18 (FIG. 8) brings 
the head 9 in correspondence with the seat of the new tool, lowers it and, 
through the electrovalve 112 and the locking device, controls the securing 
of this tool. The tool changing operation can obviously be controlled by 
program too, in order to replace a tool 26 considered worn, or when it is 
necessary to make holes of a different diameter. 
A plurality of drilling heads 9, 9', etc. (FIGS. 1, 3, 5) can be mounted on 
the same bar 10, for the purpose of drilling in parallel a plurality of 
equal supports of printed circuits. In the drawings only one of these 
additional heads is shown, the various parts of which are indicated with 
the same reference number on the head 9, provided with prime. According to 
the invention, the head 9' comprises a corresponding spindle 24' with a 
board presser 28' mounted on the quill 22'. This one is carried by a 
carriage 21' similar to the carriage 21 and is operated by its own 
servomotor 31' under the control of a corresponding transducer 102', 103'. 
However the carriage 21' is without the servomotor of the X-axis, whereby 
the head 9' becomes slave. The movement of the head 9' along the X-axis is 
controlled by the same motor 13 of the main head 9, by rigidly connecting 
the two carriages 21 and 21', at a distance equal to the width of a 
printed circuit. The two supports of printed circuits, can thus be 
obtained on a single board 27, which then shall be cut after the drilling 
or the photoetching. 
To this end, fulcrumed on the two carriages 21 and 21' (FIG. 5) are two 
corresponding supports 123, 123' provided with two corresponding pins 124, 
124' threaded in opposite direction. Located between the two supports 123, 
123' is a pulling rod 125 provided at the two ends with two threaded 
bushings 126, 126', which engage the threaded pins 124 and 124' in an 
adjustable manner, whereby the distance between the two heads 9, 9' can be 
fixed accurately. If one more than two supports of printed circuits are to 
be obtained from a single board 27, as many drilling heads mutually 
connected by several pulling rods equal to the pulling rod 125 must be 
located on the transverse bar 10. 
The spindle 24' is provided with a pneumatic device for locking the tool, 
adapted to be commanded by another electrovalve 112' operable for locking 
and unlocking the tool 26'. In order to replace the tool 26' also on the 
spindle 24' of the head 9', located on the plate 113, is another magazine 
114' (FIG. 7) of tools 26', associated with the head 9' and comprising a 
block 116' and a set of sleeves 117' for a second set of tools 26'. 
The two supports 116 and 116' are normally secured between two parallel 
bars 127 and 128 extended through the entire width of the machine. While 
the support 116 of the magazine 114 is permanently fixed between the two 
bars 127 and 128 in a predetermined transverse position, the support 116' 
of the magazine 114' may be secured, in a position to be adjustable 
according to the distance between the two heads 9, 9' selected each time, 
by means of two set screws 129, which are screwed into the bar 128 where 
crossing a vertical plate 130 guiding the boards to be drilled. 
Furthermore, secured to the carriage 21' (FIG. 5) of the head 9' is a block 
131 carrying a reference rod 132, having a frusto-conical tip and located 
at a predetermined distance at the right of the axis of the spindle 24'. 
The rod 132 ends with a manually operable knurled knob 133 and is fixed in 
the desired axial position by means of a set screw 134. Finally, the 
magazine 114' (FIG. 7) comprises a hole 135 adapted to house the rod 132 
and located at a distance from the first leftward sleeve 117' of the 
magazine 114' equal to said prefixed distance. 
After having fixed the two heads 9, 9' at the desired distance by means of 
the pulling rod 125, by a command the spindle 24 is caused to keep the 
tool 26 of the first grip 118 of the magazine 114, while the spindle 24' 
of the head 9' remains without a tool in the raised position. Then the 
support 116' of the magazine 114' is released from the bar 128 by 
unscrewing the screws 129. The magazine 114' is then manually displaced 
along the bars 127 and 128 so as to bring the hole 135 substantially 
aligned with the rod 132. Now the rod 132 is released from the screw 134, 
and through the knob 133, the rod 132 is displaced downwards. Now the 
frusto-conical end of the rod 132 engages within the hole 135 and exactly 
aligns with this latter, whereby the support 116' of the magazine 114' is 
exactly positioned at the distance from the support 116 of the magazine 
114 prefixed for the two heads 9 and 9'. Finally, the two screws 129 are 
rescrewed, thus also rigidly securing the magazine 114' to the two bars 
127 and 128, while the rod 132 is returned to the inactive raised position 
where it is locked through the screw 134. Therefore, now the tool changing 
and its integrity checking operations can be controlled simultaneously for 
both heads 9 and 9'. 
It is intended that various modifications and improvements can be made to 
the drilling machine according to the invention without departing from the 
scope of the invention. For example, one or both granite blocks 10 and 11 
may be replaced by metallic guides. Furthermore, the bearings along the 
axes X and/or Y may be of a type different than the air bearings, while 
the second head 9' may be controllable by its own servomotor also along 
the X-axis. In turn the two servomotors 31 and 31' may be feed-back 
controlled by a single transducer 103, to move the two heads 9, 9' 
synchronously along the Z-axis. Finally, for altering the distance between 
the two heads 9, 9' and/or the two magazines 114 and 114', automatic 
displacing devices may be provided, controllable through the control unit 
18.