ITTO20010142A1 - OPERATING HEAD FOR A MACHINE TOOL WITH A SWIVEL SPINDLE ON A VERTICAL AXIS. - Google Patents

Description

DESCRIPTION

The present invention refers to an operating head for a machine tool having a spindle rotating on a vertical axis, in particular for processing packs of printed circuit boards, and to a machine tool equipped with this operating head.

In known machine tools, the spindle can be axially displaced with respect to a support by a servomotor, both to bring the tool to engage the to be machined, and to determine the advancement of the tool during machining. Normally the spindle is relatively heavy, so the spindle displacement servomotor must be relatively powerful, and is made by a rotating electric motor, associated with a pair of nut screws.

The known operating heads therefore have the drawback of being of considerable weight and relatively complicated and expensive to manufacture. Furthermore, for moving the spindle with respect to a transversely movable carriage, both the carriage and the relative guides and drive means are of considerable weight and require adequately robust structures to ensure high readiness and precision in positioning the spindle.

An object of the invention is to create an operating head which requires a servomotor of reduced power, and which ensures the maximum precision of the positioning of the spindle, resulting in a limited cost, and eliminating the drawbacks of known operating heads. Another purpose of the invention is to eliminate the motion transmission means between the servomotor and the operating head.

According to the invention, the first object is achieved by an operating head for a machine tool having a spindle rotating on a vertical axis, said spindle being axially displaceable with respect to a support by a servomotor, characterized by means of balancing the weight of said spindle, said balancing means being arranged between said spindle and said support to allow a reduction in the power required of said servomotor.

In particular, the balancing means comprise a pneumatic cylinder collaborating with a piston, which engages a stop member, said cylinder and said stop member being connected one to the mandrel and the other to the support.

The second object is achieved by moving the operating head by means of a servomotor formed by a linear electric motor and by providing locking means automatically activated to lock the spindle on the support when the balancing means are inactive, or when the linear electric motor is not excited.

For a better understanding of the invention, some preferred embodiments are described here, made by way of example with the aid of the attached drawings, in which:

Figure 1 is a partial perspective view of a machine tool having two operating heads according to a first embodiment of the invention;

Figure 2 is a perspective view of a detail of a variant of the operating heads of Figure 1, on an enlarged scale and with the mandrel removed;

Figure 3 is a perspective view of the detail of Figure 2, sectioned along the line III-III;

Figure 4 is a vertical section of a detail of Figure 3, on a further enlarged scale;

Figure 5 is a perspective view of the detail of Figure 2, seen from another angle;

Figure 6 is a perspective view of the detail of Figure 5, sectioned along the line VI-VI;

Figure 7 is a diagram of the electric circuit and of the pneumatic circuit of the operating head;

Figure 8 is a partially sectioned top view of an operating head according to another embodiment of the invention;

Figure 9 is a section along the line IX-IX of Figure 8;

Figure 10 is a section along the line X-X of Figure 8.

With reference to Figure 1, 5 generically indicates an operating head for a machine tool, in particular for processing packs of printed circuit boards. The head 5 comprises a spindle 6 rotatable on a vertical axis, which is adapted to lock a tool 7, for example a drill. The spindle 6 is equipped with an electric motor not visible in the drawings, to rotate the tool 7 at high speed.

As is known, printed circuit boards are perforated with a series of small-diameter holes, arranged according to a matrix of rows and columns, so that the tools 7 are generally very small in diameter. The spindle 6 is able to be moved axially with respect to a support 8, along a direction, commonly referred to as the Z axis, both to bring the tool 7 into contact with the pack of cards to be drilled and to advance the tool 7 when drilling. This shift is done by a servomotor which will be better seen later.

According to the invention, the mandrel 6 has a substantially cylindrical external shape and can be mounted in any angular position on an organ, or mandrel-holder body, generally indicated by 11. The body 11 comprises a plate 12 of substantially rectangular shape, which it is arranged vertically and carries at least one ring 13 in one piece. The mandrel 6 is mounted on the body 11 in an easily removable way, by inserting it into the ring 13, against which it rests, by means of a retaining element, formed by an annular shoulder 14.

In particular, the plate 12 carries two axially spaced rings 13 (Figures 2 and 5), each of which is connected to the plate 12 by two reinforcement fittings 16. Each fitting 16 is also provided with two parallel straight ribs 17. At one of the two fittings 16, each ring 13 is provided with a notch 18, which defines a portion 19 of the ring 13. The portion 19 is able to flex elastically, varying the width of the notch 18 by means of a corresponding screw 21 , preferably arranged in a hole between the corresponding ribs 17.

To disassemble the mandrel 6 from the body 11, unscrew the two screws 21 and flex the portions 19 of the two rings 13, finally removing the mandrel 6 from the rings 13. To mount the mandrel 6 on the body 11, with the screws 21 sufficiently unscrewed insert the mandrel 6 into the rings 13, making the shoulder 14 rest against the upper ring 13, possibly with the interposition of a calibrated spacer ring 22. Finally, the two screws 21 are tightened, so that the mandrel 6 remains rigidly fixed on the body 11.

The support 8 is essentially constituted by a rectangular plate 23 having two vertical edges 24 and 26, and is equipped with two vertical prismatic guides 27, adjacent to the two edges 24 and 26. The plate 12 is equipped with two pairs of circulation shoes 28 of spheres, associated with the two prismatic guides 27, whereby each pair of shoes 28 slidingly engages the corresponding guide 27. The servomotor for controlling the vertical displacement of the plate 12, with respect to the support 8, comprises a linear electric motor, generally indicated with 29 , which is adapted to be controlled in a known way by a position indicator 31.

In particular, the linear motor 29 comprises a stator formed by a series of permanent magnets 32 carried by a structure 33 formed by a section 34 having a C-section, on whose wings are fixed two flat bars 35, by means of screws 36. The structure 33 is fixed on the edge 24 of the plate 23, by means of other screws 37. The permanent magnets 32 are arranged in two vertical rows and are fixed on the two bars 36, for example with a pitch of 20 mm. The linear motor 29 further comprises a group of three electrical windings 38, of which only two are partially visible in Figure 2.

The windings 38 are carried by a support element 39, fixed by means of a spacer 40 on a substantially prismatic block 41, such as to arrange the electric windings 38 between the two rows of permanent magnets 32. The block 41 is arranged in contact with the two fittings 16, on the left in Figure 2, reinforcing the two rings 13, and is equipped with two grooves 42, each adapted to engage one of the two ribs 17 of these fittings 16. In turn, the block 41 is fixed by means of two screws 43 , on a vertical wall 44 (Figure 3) of the body 11, opposite the guides 27.

The position indicator 32 comprises a scale 46 (see also Figure 5) formed by a thin strip having a series of optical marks, which is fixed on an edge 47 of the plate 12, arranged on the side opposite the block 4L. of the scale 46 are read by a position transducer 48, carried by a box-like appendage 49 of a support 51, which is fixed on the plate 23.

The operating head 5 comprises balancing means, generally indicated with 52 (Figure 2), arranged between the spindle 6 and the support 8, and can be activated automatically. The balancing means 52 serve to balance the weight of the spindle 6 during machining, so that the power required for the linear motor 29 can be reduced. The balancing means 52 comprises a pneumatic cylinder 53 with a vertical axis and integral or in one piece with the body 11, and a piston 54 sliding in the cylinder 53. A pneumostatic bushing 55 is arranged in the cylinder 53, in which the piston 54 slides and whose function will be better described later. The bushing 55 is provided with a pair of compressed air-tight seals 57, which are axially spaced. The bush 55 engages a portion 60 of the cylinder 53, having an increased internal diameter, so as to form an annular shoulder 56.

The cylinder 53 has an opening 58 at the bottom, from which a rounded end 59 of the piston 54 protrudes. The end 59 collaborates with a stop member, formed by a bracket 62, fixed by means of a screw 63 on the plate 23 of the support 8 The shelf 62 is provided with a seat in which a stop element (61) is inserted, calibrated so as to precisely define the relative position of the body 11 with respect to the support 8.

A cylindrical chamber 64 is created between the upper wall of the cylinder 53 and the upper end of the piston 54, into which a hole 66 opens (see also Figure 4). The hole 66 is provided with a fitting 67 adapted to be connected, through a flexible external duct 68 (see also Figure 7), a regulation valve 69, and a solenoid valve 70, to a compressed air tank 71. The valve 69 can be adjusted by hand, or in any known way, according to the weight of the mandrel 6, so as to partially or totally unload the weight of the mandrel 6 on the support 8. In fact, the pressure of the air in the chamber 64 keeps the end 59 of the piston 54 resting against the stop element 61, and tends to move the cylinder 53 upwards, together with the body 11 and the mandrel 6.

Between the piston 54 and the cylinder 53, the two gaskets 57 of the bushing 55 create an annular chamber 72, into which a duct 73 formed in the cylinder 53 itself opens. The duct 73 ends in a fitting 74 adapted to be connected, by means of an external duct 76 and the solenoid valve 70, to the compressed air reservoir 71. The bushing 55 is equipped with two annular rows of radial holes 75, which connect the annular chamber 72 with the gap between the piston 54 and the bushing 55. By activating the solenoid valve 70, the compressed air puts the annular chamber 72 under pressure and, through the holes 75, pressures the gap between the piston 54 and the bushing 55, which therefore acts as a pneumostatic support shoe, enormously reducing the friction between the piston 54 and the bushing 55 or the cylinder 53.

Since the operating head 5 is moved vertically by the linear electric motor 29, when the electric windings 38 (Figure 2) of the linear motor 29 are not powered, they are free to move along the stator 32, 33, so that the body 11 and the spindle 6 tend to move by gravity to the lowest position. Similarly, when the compressed air is not connected with the chamber 64, the upper wall of the cylinder 53 tends to move against the piston 54, so that by gravity the body 11 and the spindle 6 tend to move downwards. If the interruption of the electric power supply of the linear motor 29, or of the power supply of the usual compressed air compressor, is accidental, the movement by gravity of the head 5 could cause a trip, damaging the spindle 6 or the pack of cards. under processing.

In order to eliminate the risk due to the interruption of electricity, or to the lack of compressed air, the operating head 5 is equipped with locking means, generally indicated with 78 (Figure 6), which are able to automatically and instantaneously lock the spindle. 6 on the holder 8 in the current position. The locking means 78 comprise a toothed member 79 and a locking element 81, one carried by the support 8 and the other by the body 11. In particular, the toothed member is formed by a denture 79, preferably with teeth of saw, which is fixed in a depression 82 of the plate 23, by means of a pair of screws 83.

The locking element of the denture 79 is formed by an end 81 of a pneumatic piston 84 sliding in a pneumatic cylinder 86 with a horizontal axis. The end 81 is provided with a tooth adapted to engage between the teeth of the rack 79. The cylinder 86 is fixed, by means of two screws 87, on a rear portion 88 of the body 11, between the two pairs of fittings 16. Between the cylinder 86 and the piston 84 there is a chamber 89, into which a hole 91 with a fitting 92 opens. This fitting 92, through another external duct 93 (see also Figure 7), is in communication with another solenoid valve 77 connected to the outlet of the solenoid valve 70. Finally, between the piston 84 and a portion 88 there is a compression spring 90, able to push the piston 84 towards the rack 79.

When the operating head 5 is not activated, the spring 90 pushes the piston 84 towards the plate 23, so that the end 81 of the piston 84 is held in engagement with the rack 79 and the body 11 is locked on the support 8. When the windings 38 of the linear motor 29 are electrically powered, the solenoid valves 70 and 77 are also electrically powered. On the one hand, the compressed air arrives in the annular chamber 72 and then in the cylindrical chamber 64 of the cylinder 53, so that the balancing of the spindle 6. On the other hand, the compressed air arrives in the chamber 89 of the cylinder 86 overcoming the action of the spring 90, so that the end 81 disengages from the rack 79, and the head 5 is controlled by the usual control unit according to the machining program.

If for some reason the power supply of the linear motor 29 is missing, even the usual compressed air compressor and the solenoid valves 70 and 77 remain de-energized. Then the compressed air no longer reaches the chamber 89 of the cylinder 86 and the spring 90 automatically and instantaneously releases the piston 84 towards the rack 79, locking the body 11 in the current position with respect to the support 8. The spring 90 controls the locking of the body 11 also in the case in which, despite the linear motor 29 being electrically powered, for some reason the compressed air does not reach the chamber 89 of the cylinder 86.

The support 8 of the operating head 5 can be carried by a fixed upright with respect to the machine tool, or it can be constituted by a carriage 8 sliding along the usual X axis, on a crosspiece 101 (Figure 1) of the machine tool, having a prismatic recess 100. In this case the plate 23 of the carriage 8 is equipped with two pairs of ball-circulating shoes 102 (see also Figures 3 and 5), which pairs engage two prismatic guides 103 provided on the crosspiece 101.

The carriage 8 is moved along the crosspiece 101 by another linear electric motor 104, under the control of a position indicator 109 (Figure 1) of the operating head 5 along the usual axis X. The linear motor 104 comprises a stator having a series of permanent magnets 105 arranged in two rows on two flat bars 106, fixed in the recess 100 by the crosspiece 101, in a similar way to that seen for the stator 32, 33 of the linear motor 29. The linear motor 104 further comprises a group of three electric windings 107, which are carried by a support element 108, fixed on the plate 23 so as to arrange the electric windings 107 between the two rows of permanent magnets 105.

The position indicator 109 comprises a scale 110 and a position transducer 111 (see also Figure 5), respectively similar to the scale 46 and to the position transducer 48. The scale 101 is fixed on the crosspiece 101, while the transducer 111 is fixed on the support 51. Figure 1 indicates two operating heads 5, 5 'carried by two carriages 8, 8' sliding independently of each other along the crosspiece 101. The two guides 103 are then in common for the two carriages 8, 8 ', the two linear motors 104 have the stator 105, 106 in common and the position indicators 109 have the scale 110 in common. Advantageously, the two operating heads 5, 5' and the two carriages 8, 8 'can be mirror each other, so as to reduce the minimum distance, in which the two heads 5, 5 'can work simultaneously.

Figures 8-10 show another embodiment of the invention, in which the operating head 5 is equipped with adjustment means, generally indicated with 94, which can be operated to adjust the position of the mandrel with respect to the support 8 along a horizontal direction, or Y axis. In Figures 8-10, parts similar or analogous to those of the embodiment of Figures 2-6 are indicated with the same reference numbers, and will no longer be described hereinafter.

In the embodiment of Figures 8-10, the support or carriage 8 comprises two rectangular plates 95 and 96, respectively a rear plate 95 and a front plate 96, which are arranged substantially parallel to each other. The rear plate 95 carries the support element 108 of the windings of the linear motor 104, and the shoes 102 which engage the guides 103 of the X axis. The element 108 and the shoes 102 are indicated with dashed lines in Figure 9. The front plate 96 instead carries the two guides 27 of the Z axis, the stator 32, 33 of the linear motor 29, and the ratchet 79 of the locking device 78 .

The two plates 95 and 96 are rigidly fixed to each other, at the left side in Figure 8, by means of a pair of fixing screws 97. The adjustment means 94 comprise a pair of adjustment screws 98 suitable for connecting the two plates 95 and 96, in correspondence with the opposite side, i.e. on the right in Figure 8. The adjustment means also comprise a pair of specular cup springs 99 arranged between the two plates 95 and 96. The plate 96 is therefore locked on the side left and is capable of undergoing a certain elastic deformation towards the right side.

Finally, the adjustment means 94 comprise a monitoring unit, formed by a permanent magnet 80 and an analog sensor 85 for this magnet 80. In particular, the permanent magnet 80 is carried by the front plate 96, while the sensor 85 is carried by the plate 95, and is able to send signals indicating the distance from the magnet 80 to the usual control unit. In response, the control unit monitors to the operator, in a known way, the position of the body 11 along the Y axis with an accuracy of the order of one micron.

In setting up the operating head 5, by turning the adjusting screws 98 in one direction, the cup springs 99 are allowed to flex the right part of the plate 96, which moves away from the plate 95. By turning the screws 98 in the opposite direction instead , the action of the springs 99 is overcome, whereby the adjacent part of the plate 96 approaches the plate 95. All the displacements of the right part of the plate are monitored on the basis of the signals of the sensor 85. The axis of the rings 13 is thus moved along the Y axis, making the adjustment of the head 5.

If the crosspiece 101 is equipped with two or more operating heads 5, 5 ', as in Figure 1, the adjustment of the position of one of the two heads 5, 5' along the Y axis, with respect to the other head, assumes enormous importance, since it can allow the two heads 5, 5 'to work simultaneously on different areas of a row of holes in the pack of cards.

From what has been seen above, the advantages of the operating head according to the invention with respect to known operating heads are evident. First of all, the balancing means 53, 54 of the spindle 6 require for the operation a reduced power of the linear motor 29. Furthermore, the linear motor 29 greatly simplifies the construction of the operating head. Finally, the locking means 78 of the operating head with respect to the support 8, acting automatically, prevent any damage in the event of a power failure, or compressed air, to the operating head itself.

It is understood that various modifications and improvements can be made to the operating head described without departing from the scope of the claims. For example, the shape of the body 11, of the mandrel 6 and of the relative fastening means can be varied. Furthermore, the support 8 can be varied, and the head 5 can be designed for a machine tool in which the movements between the pack of cards and the spindle 6 are carried out exclusively by moving the workpiece table.

In the case of an operating head 95 equipped with the recording means 94 (Figure 8) along the Y axis, two monitoring groups 80, 85 can be provided, arranged in correspondence with the two adjustment screws 98. Furthermore, the two plates 95 and 96 can be replaced by a single body having a vertical notch, such as to create an elastically yielding portion due to the action of the adjustment screws 98.

The monitoring group 80, 85 can also comprise a proximity sensor of a position element other than the magnetic one, for example a capacitive element. Finally, in a machine tool with two operating heads 5, 5 '(Figure 1), the adjustment means 94 (Figure 8) can be provided only in one of the two heads, for example on the head 5.

Claims (28)

R I V E N D I C A Z I O N I 1. Operating head for a machine tool having a spindle (6) rotating on a vertical axis, said spindle (6) being axially displaceable with respect to a support (8) by means of a servomotor (29), characterized by balancing means (53 , 54) of the weight of said spindle (6), said balancing means (53, 54) being arranged between said spindle (6) and said support (8) to allow a reduction of the power required by said servomotor (29). 2. Operating head according to claim 1, characterized in that said balancing means (53, 54) comprise a pneumatic cylinder (53) collaborating with a piston (54), said piston (54) being able to engage a stop member (62), said cylinder (53) and said stop member (62) being connected one to said mandrel (6) and the other to said support (8). 3. Operating head according to claim 2, characterized in that said stop member is formed by a bracket (62) fixed on said support (8), said bracket (62) being provided with a seat adapted to house a stop element (61) having a calibrated thickness. 4. Operating head according to claim 2 or 3, characterized in that said piston (54) forms with said cylinder (53) a cylindrical chamber (64) in communication with a source of compressed air (71) by means of a regulating valve ( 69), said cylindrical chamber (64) being able to axially balance at least part of the weight of said mandrel (6). 5. Operating head according to claim 4, characterized in that said cylinder (53) is equipped with a pneumostatic bushing (55) which forms with said cylinder (53) an annular chamber (72) in communication with said source of compressed air ( 71) by means of an actuation solenoid valve (70), said pneumostatic bushing (55) being provided with a series of radial holes (71) to form a pneumostatic pad between said piston (54) and said cylinder (53). 6. Operating head according to claim 5, characterized in that said annular chamber (72) is formed between a pair of gaskets (57) carried by said pneumostatic bushing (55) in axially spaced positions, said pneumostatic bushing (55) being arranged in a portion (60) of said cylinder (53) having increased diameter against an annular shoulder (56) formed by said portion (60) of increased diameter. 7. Operating head according to one of the preceding claims, characterized by locking means (78) which can be activated automatically to lock said mandrel (6) on said support (8) when said balancing means (53, 54) are matt. 8. Operating head according to claims 5 and 7, characterized in that said locking means (78) are operated by elastic means (98) and are controlled by a pneumatic unit (84, 86) fed through said actuation solenoid valve (77). 9. Operating head according to claim 7 or 8, characterized in the fact that said locking means (78) comprise a toothed member (79) suitable for </iii> noec <r> zs be engaged by a locking element (81) carried by a second piston (84) collaborating with a second pneumatic cylinder (86), said toothed member (79) and said second pneumatic cylinder (86) being connected one to said support (8) and the other to said spindle (6). 10. Operating head according to claim 9, characterized in that said toothed member is formed by a ratchet (79) fixed on said support (8), said locking element (81) being horizontally movable with respect to said mandrel (6). 11. Operating head according to one of the preceding claims, characterized in that said mandrel (6) has a substantially cylindrical shape, a body (11) which can be moved vertically with respect to said support (8) being provided to mount said mandrel (6) in a manner easily removable. 12. Operating head according to claim 11, characterized in that said body (11) is provided with at least one ring (13) able to embrace said mandrel (6), at least one retaining element (14) being provided on said mandrel ( 6) to block the latter axially with respect to said ring (13). 13. Operating head according to claim 12, characterized in that said body (11) carries two rings (13) axially spaced apart and able to embrace said mandrel (6), at least one of said rings (13) being provided with a notch ( 18) to form an elastic portion (19) of said ring (13), circumferential clamping means (21) being provided for angularly locking said mandrel (6). 14. Operating head according to claim 13, characterized in that said retaining element is formed by an annular shoulder (14) of said mandrel (6) adapted to rest against one of said rings (13). 15. Operating head according to claims 2, 9 and 11, characterized in that said cylinders (53, 86) are fixed on said body (11), said stop member (62) and said toothed member (79) being fixed on said support (8). 16. Operating head according to claim 8 and one of claims 9 to 15, characterized in that said servomotor is constituted by a linear electric motor (29), said locking means (78) being activated automatically when said linear electric motor ( 29) is de-energized. 17. Operating head according to claim 16, characterized in that said support (8) is formed by a substantially rectangular plate (23) arranged vertically, said plate (23) being equipped with two parallel guides (27) engaged by two pairs of shoes (28) carried by said body (11), said linear electric motor (29) comprising a group of electric windings (23) carried by said body (11) and a stator (32, 33) parallel to said guides (27 ) and fixed on said plate (23). 18. Operating head according to claim 16 or 17, characterized in that said linear electric motor (29) is controlled by a position indicator (31) comprising a scale (46) fixed on said body (11) and a position transducer (48) carried by said plate (23). 19. Operating head according to one of claims 11 to 18, characterized in that said support (8) is provided with a vertical notch to allow a certain adjustment movement of said spindle (6) along a horizontal direction (Y), means adjustment (94) being provided to vary the width of said notch. 20. Operating head according to one of claims 11 to 18, characterized in that said support (8) is formed by two plates (95, 96) rigidly fixed to each other on one side, and connected in an adjustable way on the other by means of a sets of registration screws (98). 21. Operating head according to claim 20, characterized in that said adjustment means (94) further comprise at least one compression spring (99) arranged between said two plates (95, 96). 22. Operating head according to one of claims 19 to 21, characterized in that said recording means (94) further comprise a monitoring unit (80, 85) formed by at least one position sensor (85) able to sense the distance of a corresponding signaling element (80). 23. Operating head according to one of claims 19 to 22, characterized in that said support is formed by a carriage (8) sliding on a pair of horizontal prismatic guides (103) by another controlled linear electric motor (104) by a corresponding horizontal position indicator (109). 24. Operating head according to claim 23, characterized in that said other linear electric motor (104) comprises a stator (105, 106) integral with said horizontal prismatic guides (103) and a group of windings (107) integral with said carriage (8), said corresponding horizontal position indicator (109) comprising a scale (110) integral with said horizontal prismatic guides (103) and a position transducer (111) carried by said carriage (8). 25. Operating head according to claims 11 and 24, characterized in that said position transducers (48 and 111) are carried by a common support element (51) fixed on said carriage (28). 26. Operating head for a machine tool having a spindle (6) rotating on a vertical axis, said spindle (6) being axially displaceable with respect to a support (8) by means of a servomotor (29), characterized in that said servomotor is consisting of a linear electric motor (29), locking means (78) being provided for automatically locking said spindle (6) on said support (8) when said linear electric motor (29) is inactive. 27. Machine tool equipped with a pair of operating heads according to claim 25 or 26, characterized in that said other linear electric motors (104) have said stator (105, 106) in common, and that said horizontal position indicators (109 ) have said scale (110) also in common. 28. Operating head for a machine tool having a spindle rotating on a vertical axis, and a machine tool equipped with such an operating head, substantially as described with reference to the attached drawings.