RAITERI, Angelo (Via al Dosso 2, 6807 Taverne, IT)
| CLAIMS 1. Pressure foot device (11) for a drilling head for printed circuit boards including a body (19) that defines an axial seat (21) where the drilling spindle (15) can slide, closed by a base (23) with an opening (25) for the passage of a drilling tool (17), characterized by including at least a couple of rototranslating shafts (35,37) which are connected to corresponding drilling inserts (43, 45) which are able to move from a working configuration, in which a drilling insert is brought to the opening (25) to a resting configuration in which said opening (25) is not associated with any drilling insert and vice versa. 2. Device according to claim 1, in which in the body (19) of the device axial guiding channels (31,33) are defined in which rototranslating shafts are housed (35,37) free to rotate and to slide axially within these channels. 3. Device according to claim 1 or 2, where in corresponding base (23) there are a pair of oscillating blades (39,41) each bearing a respective insert (43,45) with a hole. 4. Device according to claim 3 in which a first drilling insert (43) has a hole (43a) with a diameter of about 7.0 mm, while a second drilling insert (45) has a hole (45a) with a diameter of about 2.0-3.0 mm for microdrilling. 5. Device according to claim 3, in which the edge of the oscillating blades (39, 41), as opposed to the inserts (43, 45), is associated with a corresponding rototranslating shaft (35, 37). 6. Device according to any of the preceding claims, in which a base (23) has seats (47, 49) for drilling inserts (43, 45). 7. Device according to any of the preceding claims, in which the rotation of the shafts (35, 37) is controlled by a pair of three-positions pneumatic actuators (51, 53), one for each rototranslating shaft fixed to the supporting structure of the drilling head (13). 8. Device according to claim 2, in which shafts (35, 37) sliding along the guiding channels (31, 33) is controlled by the motion along the "Z" axis of the drilling head (13) and is opposed by traction springs (63, 65) seated in the guiding channels (31, 33). 9. A method of controlling a pressure foot (1 1) for drilling head of printed circuit boards produced according to any one of claims 1 to 8, includes the steps of: a) bringing a first and a second insert (43.45) out of range, i.e. in a opening position; b) to bring a first insert into working position with a roto-translational movement of the shaft (37) connected to this insert (45); c) to bring said first insert in a out of range position with a roto-translational movement of the shaft (37) connected to this insert (45); d) if it is necessary to work with a different tool to bring a second drilling insert (43) into working position with a roto-translational movement of the shaft (35) connected to this insert (43); e) repeat in reverse order the steps of the previous cycle to bring back said second insert to out-of-range position. |
DESCRIPTION Field of the invention
The present invention relates to a pressure foot device for a drilling head for printed circuit boards.
More particularly, the invention concerns a pressure foot device for a drilling head which may be installed on a drilling machine for printed circuit boards.
Background information and Prior Art
As known in this particular technical sector, printed circuit boards can be made of layers of epoxy resin reinforced with fibers of glass, interspersed with sheets of copper, where each inner layer is made by photochemical processes.
Board drilling is performed in a plurality of positions allowing subsequent connection between the electrical circuits of the various layers and assembly of electronic components.
Nowadays, printed circuit boards processing demands machines which can operate with higher flexibility and productivity. For this purpose a range of drilling heads has been proposed in the past on drilling machines, typically equipped with six drilling heads, designed to simultaneously drill a corresponding stack of circuit boards.
The stack of boards is usually obtained by stacking a number of identical boards on a backup panel in Bakelite or cardboard and covering the stack with a thin aluminum foil or similar entry material. The stack is held together and placed on the tooling plate of the machine by means of two reference pins and tape.
The current drilling machine for printed circuit boards generally comprise a table translating along a first direction (Y axis), a cart translating along a second direction (X axis) orthogonal to the first which bears several drilling heads which can move along a third direction (Z axis) perpendicular to the first two.
In general, a drilling head of prior art comprises a linear or rotary motor that gives motion to the head along the Z axis, a flexible coupling, a linear guide or pneumostatic bushing, guiding the drilling head along the Z axis, a spindle carrying a drilling tool, usually driven by asynchronous motor and a pressure foot, usually consisting of a pneumatic system that applies a force to the stack of circuit boards, as close as possible to the point where the drilling takes place.
The optimal characteristics that the pressure foot must have are mainly:
ability to exercise pressure on the stack, as near as possible to the point where the drilling takes place;
ability to adjust the compression pressure of the stack;
~ ability to evacuate the drilling debris, especially in the case of microdrilling; possibility to have at least two different inserts for drilling and, more specifically, a first insert of normal size, for example with hole diameter of 7.0 mm, suitable to drill up to 6.35 mm diameter drill bits and a second insert dedicated to smaller diameters, for example with hole diameter of 2.0-3.0 mm, to drill with tool diameter less than 1.0 mm.
A first purpose of the invention is therefore to provide a pressure foot, which satisfies the above conditions in an optimal way, more reliability compared to prior art.
A further aim of the invention is to provide a pressure foot which can be associated with existing drilling heads.
Not the least purpose of the invention is to provide a pressure foot for a drilling head of that type, which is easy and economical and can therefore be produced industrially at a lower cost. Description of Invention
These and other aims are obtained with the pressure foot for a drilling head for printed circuit boards, as claimed in claims combined.
A first advantage of the invention comes from the possibility of incorporating in the pressure foot at least two different drilling inserts to be used as needed.
Another advantage of the invention comes from the ability to park these inserts in a upper position in respect of the base-plan of the pressure foot, thereby avoiding interference and the risk of collision with any protruding from the drilling plan, such as reference pins and systems for clamping the stack.
Another advantage of the invention comes from the possibility of having both inserts out of working range, thereby allowing automatic tool change and dimensional control of the tool, which are not possible with existing pressure foot.
Description of Figures
A preferred form of realization of the pressure foot for a drilling head for printed circuit boards according to the invention will be described below, merely for example, with reference to the attached figures in which:
Figures Ia through Id show a section side view of the pressure foot according to the invention, in each operating configuration;
• Figures 2a through 2c, 3 a through 3 c and 4a through 4c show the device of preceding figures in each operating configuration in frontal section, bottom view and top view, respectively;
Figure 5 is a top view of the device of preceding figures, associated with pneumatic actuators.
Description of the preferred embodiment
With reference to attached figures, the pressure foot according to the invention, which is indicated as a whole by reference 11 , is illustrated as installed on a drilling head 13 for printed circuit boards.
The drilling head 13 includes a drilling spindle 15, with electric motor, preferably of the asynchronous type, moving along the direction "Z" with respect to fixed support structure of the head 13, bearing a tool 17, for example, a drilling tool.
The drilling head 13, as per known technique, is associated with a fixed support structure (not shown), part of a unit of drilling for printed circuit boards.
The pressure foot 11 includes a body 19 that defines an axial seat 21, substantially cylindrical, where the spindle 15 can slide and a vacuum system generates a negative pressure to evacuate machining debris. The body 19 has a base 23, bottom termination of the seat 21, with an opening 25 at its center which is a passage for the drilling tool 17 when the drilling spindle 15 gets near to the base 23.
The seat 21 has also a radial hole 27 associated with a vacuum pipe 29 for machining debris removal.
In the body 19 of the pressure foot axial guiding channels 31, 33 are defined in which rototranslating shafts 35, 37, preferably hollow, are hosted free to rotate within their guiding channels 31, 33 and to slide axially within them.
At the base 23 there are a pair of oscillating blades 39, 41 each bearing a respective insert 43, 45 with an hole .
In the example depicted the first insert 43 has a hole 43a, for example 7.0 mm in diameter, that is suitable for drilling with tools up to 6.35 mm, while the second insert
45 has a smaller hole 45a, for example 2.0-3.0 mm for drilling with tools with diameter smaller than 1.0 mm.
The edge of the oscillating blades 39, 41, as opposed to the inserts 43, 45, is associated with a corresponding rototranslating shaft 35.37.
The base 23 has also the seats 47, 49 for the inserts 43, 45 mounted on the oscillating blades 39,41.
The rotation of 35,37 shafts is controlled by a pair of pneumatic actuators 51, 53, one for each rototranslating shaft, with three positions and fixed to the supporting structure of the drilling head 13 and having control pins 55, 57 cooperating with the load arms
59, 61 associated to the rototranslating shafts 35,37.
The axial sliding of the shafts 35.37 along the guiding channels 31, 33 is controlled by the motion along the "Z" axis of the drilling head 13 and is opposed by traction spring 63, 65 seated in the guiding channels 31, 33.
The work cycle of the pressure foot 11 is described as follows:
a) at the beginning of the cycle the pressure foot 11 has preferably both inserts 43, 45 out of working range, that is, opening condition (Fig. 2a, 3 a, 4a);
b) the microdrilling insert 45 is brought into working position with a roto-translational movement of the shaft 37 connectedits insert 45 (Fig.2b, 3b, 4b), said movement being obtained by the succession of a first movement impressed by the translational movement of the head along the axis "Z" to release the insert 45 from its seat 49, a second rotary motion given by actuator 53 to bring the insert 45 to the opening 25 in the base 23 and third translatory movement in the direction opposite to the first, given by the movement of the head along the "Z" axis to bring the insert 45 against the base 23;
c) the microdrilling drilling insert 45 is brought into out-of-range position with a roto- translational movement of the shaft 37 connected with said insert 45 for the drilling tool 17 change (Fig. 2a, 3 a, 4a), said movement being obtained by reverse order of the steps described in the preceding paragraph;
d) if it is necessary to operate with a drilling tool of larger diameter (typically diameter greater than 1.0 mm) the standard-drilling insert 43 is taken to working position with a roto-translating movement of the shaft 35 connected to said insert 43 (Fig.2c, 3c, 4c), said movement being obtained by a sequence of steps identical to that described in paragraph a);
e) repeating the steps of the previous cycle in reverse order brings back said insert 43 in out-of-range position.
Advantageously, according to the invention, movements of rototranslation of shafts 35,37 are controlled by control devices hosted on the fixed part of the drilling head 13. In this way the use of mobile tubing connected to pressure foot is avoided. This is advantageous because the pressure foot makes small movements of approximately hundreds of cycles per minute, which may in time deteriorate the air supply tubing, as found in the actual solutions on the market.