Tool-change system for a machine tool with a number of machining heads

The tools of the various machining heads are housed on a common drum, which is remote from the heads and rotated to select a given row of tools. At each head, there is provided an intermediate station having a container housing a row of tools; and a shuttle provides for sequentially transferring the tools between the drum and the intermediate stations. Each container is rotated 90.degree. between a position cooperating with the shuttle and a position cooperating with a device for exchanging the tools between the head and the container. The container is also movable with respect to the device to select the location of the tool to be changed.

BACKGROUND OF THE INVENTION 
The present invention relates to a tool-change system for a machine tool 
with a number of machining heads, in particular for machining printed 
circuit boards. 
Various tool-change systems are known for machine tools of the above type, 
each machining head of which normally has a respective tool store and a 
respective device for exchanging tools between the store and the head. In 
one known machine, the various stores are located on the machine bed, and 
the worktable carries a number of tool-change devices. 
In another known machine, each head is provided with a drum supporting a 
number of rows of tools, and which rotates selectively on the machine bed 
to present the tool-change device with the row containing the required 
tool. In this case, too, the tool-change device is carried on the table. 
The tool-change systems of the above known machines have several drawbacks. 
In particular, they call for a number of identical members for supporting 
and selecting the tools, thus increasing the cost of the machine. 
Moreover, they occupy considerable space on the machine bed, thus 
enormously increasing the size of the machine. And finally, to change the 
tool stores, the machine must be arrested, thus also increasing the 
running cost of the machine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a highly 
straightforward, reliable tool-change system for a machine tool with a 
number of machining heads, designed to eliminate the aforementioned 
drawbacks typically associated with known systems. 
According to the present invention, there is provided a tool-change system 
for a machine tool with a number of machining heads, in particular for 
machining printed circuit boards; characterized in that the tools for said 
heads are housed in a common store, and are transferred selectively 
between said store and a group of intermediate stations; changing means 
being provided to change the used tool on each head with a tool 
transferred to one of said stations.

DETAILED DESCRIPTION OF THE INVENTION 
Number 10 in FIG. 1 indicates as a whole a machine tool for machining 
printed circuit boards, and which comprises a bed 11 supporting two 
lateral uprights 13, only the left-hand one of which is shown in the 
drawings. Uprights 13 are fitted with a steel crosspiece 14 comprising a 
horizontal plate 16 and two vertical plates 17 (see also FIG. 2); and 
machine 10 also comprises a worktable 18 movable in known manner in a 
first direction hereinafter referred to as axis Y. 
A carriage 44 travels along crosspiece 14 in a second direction hereinafter 
referred to as axis X, and comprises two parallel bars 46 connected to 
each other by a number of crosspieces 47. Each bar 46 is a steel box bar, 
and is reinforced by a pair of rectangular-section bars 45 and 50; each 
pair of bars 45, 50 is fitted with a respective row of machining heads 33, 
e.g. comprising four heads 33; each two corresponding heads in the two 
rows form a pair of heads 33, so that carriage 44 carries a total of eight 
heads 33; and each head 33 comprises a vertical tool-holder spindle 34 for 
receiving a tool 36, and which is moved along a vertical axis Z by a 
reversible numeric-control electric motor (not shown). 
Machining of the printed circuit boards mainly comprises drilling, but may 
also comprise milling operations. The boards are arranged in packs, each 
of which is placed for machining on a fixture 38 fitted to table 18 and 
associated with a respective head 33. Table 18 therefore carries eight 
fixtures 38 arranged in two rows, with a gap 42 between adjacent pairs of 
fixtures 38. 
The first pair of fixtures 38 on the left is flanked by a first pair of 
devices 43 for changing tool 36, each device being associated with a 
respective head 33 in the corresponding pair; each of the spaces 42 
between pairs of fixtures 38 houses a respective pair of devices 43 
associated with heads 33 in the next pair to the right; each device 43 is 
defined by a pneumatic gripper 40 for removing a tool 36, e.g. from 
spindle 34; and gripper 40 is moved along the Z axis in known manner by a 
corresponding pneumatic piston (not shown). 
According to the invention, the system for changing tools 36 comprises a 
store 51 (indicated by a dash line in FIG. 1 for the sake of simplicity) 
which is common to tools 36 of all of heads 33 and is located outwards of 
crosspiece 14. More specifically, store 51 (FIGS. 2 and 4) is fitted to a 
support indicated as a whole by 52, and which in turn is fitted to the 
left-hand upright 13 and comprises a bracket 53 extending forwards and 
having a vertical wall 54 fitted with a rotary shaft 56 parallel to 
crosspiece 14. 
Store 51 is defined by a drum 57 fittable removably to shaft 56 
substantially as described in European Patent N. 541.020. More 
specifically, drum 57 houses a number of--e.g. twenty--rows of tools 36; 
each row is located in a predetermined angular position on drum 57, and 
may receive three clips or strips 58 of tools 36, so that store 51 has a 
capacity for an extremely large number of tools 36. 
Each strip 58, in itself known, is defined by a body made of plastic 
material and having a number of locations or seats for tools 36, e.g. of 
the collarless type. Each tool 36 is retained frictionally inside the 
respective seat by elastic elements on the body of strip 58, and is 
withdrawn from and inserted inside the seat axially. Drum 57 also 
comprises a guard 60 for tools 36. 
Wall 54 of bracket 53 is also fitted with an electric step motor 59, which, 
by means of a belt 61, rotates drum 57 to move the required row of tools 
36 into a transfer position T, in which tools 36 are positioned 
horizontally with the tips facing the rear of machine 10. To select the 
row of tools 36, store 51 is therefore moved in a plane perpendicular to 
crosspiece 14. 
At each pair of machining heads 33 on carriage 44, an intermediate station 
62 (FIG. 1) is provided for temporarily housing the new tools 36 to be 
fitted to spindle 34 of head 33, and the used tools 36 extracted from 
spindle 34 by tool-change device 43. Each intermediate station 62 
comprises a container 63 (FIGS. 5 and 6) for housing a predetermined 
number of tools 36 in a row parallel to crosspiece 14. Container 63 is 
defined by a body similar to that of strips 58 on drum 57 but normally 
with no tools 36, and is fitted to a support 64 integral with a plate 65 
fitted underneath crosspiece 14. 
More specifically, support 64 comprises a guide defined by two prismatic 
bars 66 (FIG. 7) parallel to crosspiece 14 and between which container 63 
is housed in sliding manner. Bars 66 have a median plane M perpendicular 
to the axes of tools 36, and are connected to each other by two sides 67, 
each having a pin 68. Support 64 comprises two sides 69 to which the two 
pins 68 are fitted in rotary manner; and, in the FIG. 7 position, the axis 
of pins 68 is below the median plane N of bars 66. 
An appendix 70 of support 64 is fitted with a pneumatic motor 71 having a 
shaft 72, which is rotated between two positions at 90.degree. to each 
other, and is connected by a joint 73 to the adjacent pin 68, so that bars 
66 are rotated 90.degree. together with container 63. Bars 66 are normally 
so positioned by motor 71 that container 63 positions tools 36 
horizontally and aligned with the row of tools 36 on drum 57 in transfer 
position T. When rotated 90.degree., motor 71, by means of bars 66, moves 
container 63 into a vertical tool-change position, with the tips of the 
tools facing downwards as shown in FIGS. 5 and 7. 
A spring 75 is fitted between a pin 80 on support 64 and one end 74 of 
container 63, and provides for normally holding container 63 against a 
stop 76 fitted to bars 66. The front rectangular-section bar 45 of 
carriage 44 (FIGS. 1 and 6) is fitted, to the left of respective head 33, 
with a plate 77 supporting an arm 78, which has an appendix 79 for 
engaging end 74 of container 63. 
When container 63 is rotated into the tool-change position, appendix 79 
draws container 63 parallel to crosspiece 14, in opposition to spring 75, 
to select each time the location of tool 36 to be changed. Conversely, 
when container 63 is set with tools 36 positioned horizontally, appendix 
79, by virtue of the position of pins 68, fails to encounter bars 66 and 
therefore travels freely. 
The system for changing tools 36 also comprises a transfer device indicated 
as a whole by 81 and which is common to all of intermediate stations 62 
and provides for selectively transferring tools 36 between store 51 and 
intermediate stations 62, which are served sequentially. Device 81 
comprises a shuttle 82 fitted to a known linear actuator 83, which extends 
rightwards substantially the whole length of crosspiece 14, and which, 
leftwards, extends through an opening 80 in upright 13 and beyond drum 57. 
More specifically, actuator 83 is fitted to crosspiece 14 by supporting 
means comprising an arm 92 (FIGS. 2 and 3) extending outwards of the 
left-hand upright 13, and comprises a toothed belt 84 cooperating with 
vertical-axis pulleys, one of which is rotated selectively by an electric 
motor 85. Shuttle 82 comprises a slide 86 fitted to the front portion of 
belt 84 and supporting a horizontal guide 87 perpendicular to the axis of 
drum 57 to guide a gripper 88 for gripping a tool 36. 
Gripper 88 is substantially similar to grippers 40 for changing tools 36, 
is oriented with two movable jaws in a vertical plane, and is moved along 
guide 87 by a pneumatic cylinder 89 (FIG. 4) not shown in FIG. 2. The 
left-hand upright 13 is also fitted with a support 91 fitted removably 
with a container 90 for discarded tools 36; and each spindle 34 comprises 
a known tool-condition sensor (not shown) for indicating to a control unit 
when the respective tool 36 is no longer serviceable due to damage or 
wear. 
The system for changing tools 36 operates as follows. 
To begin with, it is assumed drum 57 (FIG. 4) with tools 36 is fitted to 
shaft 56; each of spindles 34 is fitted with a tool 36; some already-used 
tools 36 are housed inside containers 63 (FIG. 5); and containers 63 are 
set by motor 71 to the angular position shown by the dash line in FIG. 7 
and in which the tools are positioned horizontally. 
It is also assumed the packs of printed circuit boards for machining are 
fitted onto fixtures 38 (FIG. 1); machine 10 is performing the set 
drilling and milling cycles using the tools 36 in spindles 34; and, at 
each cycle, the control unit positions table 18 along axis Y and carriage 
44 along axis X, and then activates spindles 34 of heads 33 to 
simultaneously machine the packs of printed circuit boards. 
In the course of the above machining cycles, the control unit operates 
transfer device 81 to perform a series of transfer cycles of tools 36 
between drum 57 (FIG. 4) and intermediate stations 62. At each cycle, the 
transfer of a new tool 36 from drum 57 to intermediate station 62 
alternates with the return of a used tool 36 from station 62 to drum 57. 
To begin with, drum 57 (FIG. 2) is rotated to position the row containing 
the tool/s 36 to be withdrawn into transfer position T, if the row is not 
already in the transfer position. At the same time, actuator 83 is 
operated to position shuttle 82, together with gripper 88, opposite the 
tool 36 to be transferred. Pneumatic cylinder 89 (FIG. 4) is then operated 
so that gripper 88 engages tool 36; gripper 88 is closed; and cylinder 89 
is again operated to extract tool 36 from drum 57. 
Actuator 83 is then operated to position shuttle 82, together with gripper 
88, opposite the location in container 63 (FIGS. 1 and 7) associated with 
the first pair of machining heads 33, into which the new tool 36 is to be 
inserted; cylinder 89 (FIG. 4) is again operated so that gripper 88 
inserts the new tool 36 inside the selected location; and gripper 88 is 
then opened and moved by actuator 83 to the location in container 63 
containing the tool 36 to be transferred to drum 57. Whenever possible, 
the control unit is so programmed that the location into which the new 
tool 36 is inserted is adjacent to that from which the used tool 36 is 
withdrawn. 
Once gripper 88 is closed, actuator 83 is operated to position shuttle 82, 
together with gripper 88, opposite the location in the row on drum 57 into 
which the used tool 36 is to be inserted. Operating gripper 88 in the same 
way as before to insert tool 36 inside container 63, the used tool 36 is 
then inserted inside the respective strip 58 on the drum. 
If a given used tool 36 has been memorized by the control unit as being no 
longer serviceable, the control unit arrests actuator 83 and shuttle 82 at 
container 90 (FIG. 1) during the transfer cycle to drum 57, and gripper 88 
is opened to drop the discarded tool 36 into container 90. The above 
transfer cycle is repeated sequentially for all of intermediate stations 
62, and may also be repeated to transfer more than one tool 36 to each 
station 62 and so form a standby stock of tools 36 in containers 63. 
To change tools 36 in spindles 34, operation of transfer device 81 is 
suspended temporarily. To begin with, the control unit operates pneumatic 
motors 71 (FIGS. 5 and 7) to rotate bars 66, together with containers 63, 
to position tools 36 vertically; the control unit then moves carriage 44 
(FIGS. 1 and 2) and table 18 along respective axes X and Y to align the 
axes of spindles 34 with grippers 40 for changing tools 36; and grippers 
40 are then activated by the pneumatic cylinders to withdraw the 
respective used tools 36 from spindles 34. 
The control unit then moves carriage 44 selectively leftwards so that 
appendixes 79 (FIGS. 5 and 6) of arms 78 engage ends 74 of respective 
containers 63; each container 63 is drawn in opposition to spring 75 to 
align the location in container 63 into which the used tool 36 is to be 
inserted with the gripper 40 (FIG. 1) relative to the front machining head 
33 in each pair; and gripper 40 then inserts the used tool 36 inside 
container 63. The above operation is repeated to insert into containers 63 
the tools 36 extracted by grippers 40 relative to the machining heads 33 
in the rear row. 
Two successive operations, similar to those described above, are then 
performed, whereby appendixes 79 position containers 63 to withdraw the 
new tools 36 first by grippers 40 of the front row of heads 33, and then 
by grippers 40 of the rear row of heads 33. Once carriage 44 and table 18 
are repositioned, grippers 40 are operated simultaneously to insert the 
new tools 36 inside respective spindles 34 and so recommence machining the 
packs of printed circuit boards and transferring tools 36 between common 
store 51 and intermediate stations 62. 
Drum 57 of tools 36 may be changed by the operator even while the packs of 
printed circuit boards are being machined, by simply temporarily 
suspending transfer of tools 36 by device 81. By virtue of each container 
63 containing a number of tools 36, machine 10, during replacement of drum 
57, may not only continue working with the tools 36 already inserted 
inside spindles 34, but may also perform several tool-change cycles 
between spindles 34 and containers 63. 
As compared with known systems, the advantages of the tool-change system 
according to the invention will be clear from the foregoing description. 
In particular, common store 51 provides for simplifying the structure of 
machine 10. Moreover, machine 10 is far more compact by eliminating the 
individual stores of the various machining heads 33. And finally, using 
intermediate stations 62 for tools 36 and a remote common store 51 
provides for eliminating the downtime incurred on known machine tools to 
change the stores, thus reducing the running cost of the machine. 
Clearly, changes may be made to the system as described and illustrated 
herein without, however, departing from the scope of the accompanying 
claims. For example, drum 57 may be replaced by a drawer-type store moved 
in known manner in a direction perpendicular to crosspiece 14; machine 10 
may comprise only one row of machining heads 33, possibly movable 
independently of one another along crosspiece 14; and machine 10 may 
comprise an intermediate station 62 for each head 33, even in the case of 
heads 33 arranged in two rows. 
Each device 43 for changing tools 36 may provide for serving at least two 
machining heads 33; container 63 may be fitted to support 64 for 
troublefree replacement by hand; and intermediate station 62 may comprise 
any number of locations, greater than two, for tools 36, and may be moved 
with respect to tool-change grippers 40 by any type of actuator 
independent of the movement of carriage 44.