Patent Document

[0001]    The present invention relates to a device for the high-speed drilling of boards for printed circuits and the like. 
       TECHNICAL FIELD 
       [0002]    When machining boards for printed circuits, the board has to be drilled in at least some of the zones of welding of the circuit components. The current trend is towards an ongoing increase in the density of holes per unit of area and a reduction of their diameter. 
       TECHNOLOGICAL BACKGROUND 
       [0003]    For this purpose, use is generally made of high-speed electric mandrels whose drill head is guided along an axis (z) to and from the board to be drilled. The devices in question comprise a workpiece-pressing device which is adapted to press the board at the drilling point before and during the actual drilling. The workpiece-pressing device therefore has to be positioned, keyed and pressed on the board and then raised away from the board for the execution of each individual hole. It is therefore subject to many displacements towards and away from the board during drilling. 
         [0004]    Bearing in mind the speeds involved (the device of the invention is adapted to enable more than 20 holes to be dilled per second), even apparently small mass displacements become a critical factor. 
         [0005]    The drilling devices used up to now do not take appropriate account of this critical factor and have thus played their pat in limiting the maximum drilling speed that has up to now been practicable. At present, no more than eight holes per second can be drilled with the fastest devices, which is far from market requirements in terms of the economic machining of the boards in question. 
       DESCRIPTION OF THE INVENTION 
       [0006]    In the light of the above, the technical problem underlying the present invention is that of providing a drilling device for printed circuit boards which is structurally and functionally designed to enable the limits of the cited prior art to be remedied. 
         [0007]    In the context of this problem, the main object of the present invention is to provide a drilling device which substantially reduces the masses subject to acceleration during the various drilling phases. 
         [0008]    This problem is resolved and this and other objects are achieved by a drilling device embodied in accordance with the accompanying claims. 
         [0009]    The notion of the solution underlying the present invention is based on the observation that known devices involve an unnecessary movement of the workpiece-pressing device which is normally connected to the drill head and therefore follows its movements towards and away from the board. According to the invention, the device is caused to move independently with respect to the drill head, and is actuated by an independent positioning actuator only in the initial stage of positioning and adjustment of the so-called “planar circuit” while any other movement towards and away from the board to be drilled is carried out by means of an independent actuator, for instance of piezoelectric type, actuated at a frequency equal to the drilling frequency so as to work in a synchronised manner with the drill head. An actuator of voice coil or like type may be efficiently used as an alternative to a piezoelectric actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The characteristic features and advantages of the invention are set out in the following detailed description of a preferred embodiment thereof, shown by way of non-limiting example in the accompanying drawings, in which: 
           [0011]      FIG. 1  is a perspective view of a device for the high-speed drilling of boards for printed circuits and the like; 
           [0012]      FIG. 2  is a front elevation of the device of  FIG. 1 ; 
           [0013]      FIG. 3  is a perspective view, in longitudinal section, of a detail of the device of  FIG. 1 ; 
           [0014]      FIG. 4  is a perspective view of a variant of the device of the invention. 
       
    
    
     PREFERRED EMBODIMENT OF THE INVENTION 
       [0015]    In the drawings, a device for the high-speed drilling of boards for printed circuits and the like is shown overall by  1 . The device  1  comprises a support  2  on which a linear actuator  3  is mounted, whose rod  3   a  acts on a first carriage  4 . The first carriage  4  is mounted to slide on the support  2  by means of guides  5  and shoes  6 ; a second carriage  8  which may also slide on the support  2  by means of a second actuator  3   b  is mounted on different guides  7  and comprises similar shoes (not shown). The second carriage  8  is normally locked with respect to the support  2 . 
         [0016]    A drill head  11  is mounted on the first carriage  4  and comprises a mandrel  12  able to drive a drill bit  13  in rotation at high speed. The actuator  3  displaces the first carriage  4  towards and away from a board P to be drilled during the desired drilling movements. 
         [0017]    The second carriage, together with an arm  15  mounted thereon, is part of a workpiece-pressing device shown overall by 16 which is adapted to press the board P against a working surface (not shown) during drilling by means of the bit  13 . 
         [0018]    The arm  15  is embodied as a leaf spring extending in a cantilevered and projecting manner from a plate  17  which at the bottom closes an actuator member  18 . The arm  15  is made in one piece with the plate  17  and ends at one of its roots in a weakened line  19   a  cut into the plate  17  which is adapted to create a preferential resiliently yielding zone about which the arm  15  tends to oscillate when actuated by the actuator  18 . 
         [0019]    The actuator  18  is of piezoelectric type and is adapted to promote the alternating oscillating movement of the arm  15  about the weakened line  19   a . At the free end of the arm  15 , opposite its root, there is formed a support  15   c  on which a pressure member  19  is mounted and is free to oscillate about a diametric axis  20  so as to be disposed coplanar to the board P when bearing thereon. The pressure member  19  is shaped as an annular bushing with a crown  21  of greater diameter and a crown  22  of smaller diameter which are coaxial and both provided with a central hole  23 . 
         [0020]    A variant of the device  1  is shown in  FIG. 4 . Details similar to those of the preceding embodiment bear the same reference numerals. The actuator of the embodiment of  FIG. 4 , shown by  118 , is of the type known as a voice coil actuator and is connected by means of a control rod  119  to the arm  115  of the workpiece-pressing device  16 . The arm  115  is in turn hinged at the location of a pin  120  on a fork support  121  which is stationary on the carriage  8 . The actuation of the actuator  118  therefore generates an oscillation, whose frequency can be controlled and adjusted, of the arm  115  about the pin  120  thereby raising and lowering the pressure member  19  towards and away from the board P to be drilled. 
         [0021]    The device  1  operates as follows. 
         [0022]    The drilling device  1  is actuated by means of a computerised digital control which does not form part of the subject matter of the present invention. The first operation prior to the stage of drilling of the board P is therefore to determine the so-called “planar circuit” position so that the control learns for which coordinates the head  11  and the workpiece pressing device  16  are physically in a predetermined position with respect to the board P. 
         [0023]    For this first operation, the second carriage  8  displaces the workpiece-pressing device  16  until it brings the latter to contact the board P with a predetermined contact pressure. When the assembly is raised by a predetermined extent, the second carriage  8  is locked with respect to the support  2 . In these conditions, the linear actuator  3  governs only the actuation of the drill head  11  and is subject to the forces of inertia relating only to its mass which are substantially smaller than those relating to the overall mass of the head  11  and workpiece-pressing device  16 . It will be appreciated that the reduction of the masses in question in turn makes it possible to reduce the dimensions of the linear actuator  3  and its rod  3   a  which helps further to reduce the overall forces of inertia involved. 
         [0024]    The workpiece-pressing device  16  is actuated towards and away from the board P by the piezoelectric actuator  18  or voice coil actuator  118 , whose action is adjusted by varying the supply frequency thereof. This frequency variation, obtained for instance by an inverter, corresponds to the same frequency variation of the cycle of pressure and raising of the arm  15  (as a result of the known piezoelectric properties of piezoelectric actuators and electromagnetic properties of voice coil actuators) and therefore of the pressure member  19  which alternates between a position pressed against the board P and a position raised therefrom. The supply frequency of the actuator is therefore adjusted to coincide with the frequency of the drilling cycle carried out by means of the bit  13 . 
         [0025]    Moreover, varying the distance of the board P to be drilled with respect to the workpiece-pressing device  16  adjusts the pressure exerted by the pressure member on the board, both because the resilient reaction opposed by the arm  15  varies because the resulting displacement differs and because the pressure exerted by the actuator  18 ,  118  varies as its stroke varies, without having to act on other (hydraulic or pneumatic) operating parameters of the device. 
         [0026]    The invention thus resolves the problem set out above and offers many advantages with respect to the technical solutions known up to now, all of which focus chiefly on increasing the drilling speed and the hourly output that can be achieved.

Technology Category: h