FR2815896A1 - CNC MACHINING CENTER - Google Patents

Abstract

The invention relates to a numerically controlled machining center, which relates to a machining center which comprises a frame support foundation (1), a support base (2) projecting from the foundation (1) along a first coordinate axis, a first lead screw (22) having two opposite pitch sections along the first coordinate axis, a table assembly (3) comprising a first nut (312) cooperating with the pitch section reverse of the first lead screw (22), and a tool holder assembly (4) comprising a second nut (412) cooperating with the positive pitch section of the first lead screw (22) so that the assembly ( 4) with a tool holder moves in translation in the opposite direction to the direction of movement of the assembly (3) at the machining table when the first lead screw (22) rotates. Application to machine tools.

Description

The present invention relates to a numerically controlled machining center

  and, more precisely, such a machining center having a lead screw comprising parts of positive pitch and reverse pitch respectively, associated with two fixed nuts respectively with a tool holder assembly and a machining table assembly so that the tool holder assembly

  and the table assembly are moved simultaneously

  in opposite directions along at least one axis of coordination

  born, so that the relative speed of movement of the tool holder assembly and the machining table assembly is significantly increased and reduces the time without machining a

  CNC machining center.

  In general, for machining a workpiece with a tool, a numerically controlled machine tool is equipped with a device for advancing the tool towards the workpiece during a machining period and with a change device. and adjusting the relative positions of the tool and the workpiece during a period without machining. During the machining period, the speed of advance of the tool towards the workpiece is determined by the characteristics of the material to be machined, and

  should not be changed or increased arbitrarily.

  However, if the speed of movement or adjustment of the relative positions of the tool and the workpiece in a period without machining is increased, the overall machining speed and the efficiency of the machining center increase

significantly.

  FIG. 1 represents a conventional numerically controlled machining center having a machining table T which cooperates with a seat T1 for translational movement thanks to a nut (not shown) associated with a lead screw R, so that the machining table T can be moved along the X axis on the seat Tl for translational movement, when a servomotor M rotates the lead screw R. The seat Tl cooperates with a foundation F for supporting the frame at the using an additional screw and nut mechanism, so that the seat Tl can move alternately along the axis Y above the foundation F for supporting the frame. Similarly, a tool holder B is placed on a vertical base FV by using a nut N and a lead screw R, so that the tool holder B can be moved in translation along the axis Z on the FV base. Consequently, the relative positions along three coordinate axes between the tool holder B and the machining table T are all

  adjustable so that the machining operation is easy.

  We now refer to the conventional use of the screw and nut mechanism, that is to say of the transmission mechanism which includes the vismere R and the nut N shown in FIG. 1, for changing the positions. relative to the tool holder and the working table, when the speed of the tool holder must be increased so that the tool approaches or moves away from the working table; the operation can only be obtained by increasing the speed of rotation of the lead screw by using a higher speed servomotor. However, it can be seen that none of the servomotors existing on the market makes it possible to obtain a satisfactory speed of movement of the tool holder and the machining table relative to

  the other during the period without machining.

  In particular, when the conventional screw mechanism

  mother and nut is used for the alternative displacement of the tool holder in vertical direction, for example when the tool holder B is moved along the vertical axis Z by the mother screw R in association with the nut N of the center conventional numerical control machining shown in Figure 1, the load on the servomotor M which rotates the lead screw R to move the tool holder B up is much greater than the load on the servomotor during movement

  towards the bottom of the tool holder B, given the weight of the

  Tool B. Not only is the servo motor life reduced, but the adjustment of the operating speed is not easy. For the solution of this problem posed by the fact that the actuator collects different loads when it moves the lead screw up and down to move the tool holder B, the known technique implements a chain, a cable or the like for connecting a counterweight which balances the weight of the tool holder B and avoids the problem posed by the loads

  different received by the servomotor during displacements

  cements up and down the tool holder B. Although this characteristic can be used in practice, the machine tool then has a complex, bulky and inconvenient construction, and the manufacturing and maintenance pose

problems.

  We now refer to the command machining center

  conventional digital shown in Figure 1; The door-

  tool B is moved up or down when the servomotor M drives the lead screw R in rotation in one direction or the other. Such a construction and such an operation, using a servomotor M in association with a screw and nut mechanism for the upward and downward movement of the tool holder B, poses a problem, because if the supply electric is interrupted unexpectedly or if the servomotor is not energized, the weight of the tool holder B creates a torque which can rotate the lead screw R which can rotate freely, and gradually moves downward under the action of the weight of tool holder B. This behavior can cause the tool holder to collide with the workpiece, the worktable

  or other parts of the machine and may damage them.

  The subject of the invention is the provision of a numerically controlled machining center in which the relative speed of movement, along at least one coordinate axis, of a tool and a part is double the

  relative movement speed of the conventional mechanism obtained

  naked with a lead screw and a nut, during a simple displacement

  tool or workpiece cement. The invention applies to a lead screw having two sections with opposite threads, that is to say a positive thread and a reverse thread, in combination with two nuts fixed separately to a tool holder assembly and a machining table assembly for carrying out the relative displacement or offset of the tool and the workpiece, so that the time without machining of the numerically controlled machining center is significantly reduced, and the

  overall machining speed and yield are increased.

  The subject of the invention is also the production of a numerically controlled machining center in which a tool holder assembly and a machining table assembly are placed so that they can move alternately along a vertical axis thanks to to a lead screw having two sections with opposite threads, that is to say a positive thread and a reverse thread, in combination with two nuts fixed respectively to the tool holder assembly and to the assembly machining table, so that a servo motor, when it rotates the lead screw in one direction or the other to move the tool holder assembly and the machining table assembly one relative to each other in a vertical direction, undergoes almost identical loads, without

  the use of an additional counterweight.

  The invention also relates to a numerically controlled machining center which makes it possible to avoid collisions between the tool holder and the workpiece or the machine, when electrical energy is inadvertently removed or

  when the actuator is not supplied.

  Other characteristics and advantages of the invention

  will be better understood on reading the description which will

  follow example embodiments, made with reference to the accompanying drawings in which: FIG. 1 is a schematic perspective view of a conventional numerically controlled machining center representing the machining table and the tool holder which can be move relative to each other along X, Y and Z axes; FIG. 2 is a schematic perspective view of a numerically controlled machining center in a first embodiment of the invention, indicating the relative movement between the machining table and the tool holder along a vertical axis, that is to say a Z axis, produced by means of a lead screw which has a positive thread section and an opposite direction thread section, intended to be associated with a respective nut fixed to the machining table and another nut fixed

  to the tool holder, so that the machining table and the

  tool can be moved relative to each other at double speed along the vertical axis Z; FIG. 3 is a schematic view of the lead screw according to the invention having a section with positive pitch thread and a section with reverse pitch thread associated with two nuts fixed respectively to the machining table and to the tool holder, indicating that the lead screw turns clockwise

  of a watch so that the machining table and the holder

  tool are reconciled; FIG. 4 represents another schematic view of lead screw according to the invention, when it rotates anti-clockwise, so that the machining table and the tool holder move apart one of the other; Figure 5 is a perspective view of a CNC machining center in a second preferred embodiment of the invention; and Figure 6 is a schematic perspective view of a CNC machining center in a third mode

  preferred embodiment of the invention.

  We use in the following certain expressions for the

  convenience of description. For example, the expressions "to

  front "," back "," right "," left "," upper "

  and "lower" indicate the directions on the accompanying drawings

  which we refer to, the expressions "internal" or "inward" and "external" or "outward" refer

  respectively to the directions of reconciliation and spreading

  ment of the center of the element considered, and the terms

  "radial" and "axial" refer respectively to directions

  tions or planes perpendicular and parallel to the long axis

  central tudinal of the element referenced. It should be considered that other related terms are sometimes used for convenience, without any restriction. To facilitate the

  representation and description, X, Y and Z axes

  indicated below correspond to three axes of

  coordinates perpendicular to each other and represented

  felt on the drawings. The vertical direction is considered to be practically perpendicular to the center. Identical references designate similar elements on

the different figures.

  As shown in FIG. 2, a numerically controlled machining center in a first embodiment of the invention comprises a foundation 1 for frame support, a base 2 for support, a set 3 with a machining table, and a tool holder assembly 4. The support base 2 is a vertical base, which protrudes above the foundation 1 and which

  comprises two vertical rails 21 parallel to each other.

  In FIGS. 2 and 3, a lead screw 22 having two opposite pitch sections, that is to say a positive pitch section 221 and a reverse pitch section 222, is disposed on the base 2 along the axis vertical Z and can rotate in one direction and

  in the other under the control of an Ml servomotor.

  The assembly 3 with a machining table is intended to support and fix a workpiece, and it comprises a lower seat 31 of axis Z and a machining table 32, the lower seat 31 being formed with two slides 311 intended to cooperate with the rails 21 for guiding the seat

  lower 31 when it moves alternately in the direction

  vertical axis Z on the vertical base 2. A nut 312 is fixed to the lower seat 31 so that it cooperates with the reverse pitch section 222 of the lead screw 22 so that the lower seat 31 moves alternately along the 'Z axis, when the lead screw 22 is rotated by the actuator Ml. The lower seat 31 is arranged along an axis X with two parallel rails 313 and a lead screw 314 mounted so that it can rotate on the lower seat 31

  and driven in rotation by an M22 servomotor.

  The machining table 32 has two slides 321 cooperating with the rails 313 and a nut (not shown) cooperating with the lead screw 314 so that the machining table 32 moves in translation on the rails 313 along the axis X

  when the M22 servomotor turns the lead screw 314.

  The tool holder assembly 4 comprises an upper seat 41 of axis Z, an upper seat 42 of axis X and a seat 43 of displacement in translation of axis Y. The upper seat 41

  Z axis, like the lower seat 31 Z axis described above

  demment, has two slides 411 intended to cooperate with the rails 21 and a nut 412 intended to cooperate with the positive pitch section 221 of the lead screw 22, so that the upper seat of axis Z moves vertically parallel to the 'Z axis when the lead screw 2 is rotated by the MI servomotor. The upper seat 41 of axis Z has two parallel rails 413 of axis X and a lead screw 414 mounted so that it can rotate on the upper seat 41 along the axis X, and it is rotated by a

M21 servo motor.

  The upper seat 42 of axis X has two parallel slides 421 intended to cooperate with the rails 413 and a nut (not shown) intended to cooperate with the lead screw 414, so that the upper seat 42 of axis X can be move in translation on the rail 413 along the X axis when the lead screw 414 is rotated by the servomotor M21. The upper seat 42 of axis X also has, parallel to the axis Y, two parallel rails 423 and a lead screw 424 mounted so that it can rotate on the upper seat 42 of axis X along the axis Y and driven by a

servomotor (not shown).

  The seat 43 for translational movement of the Y axis is intended to carry a tool-holder spindle (without numerical reference) which comprises two slides 431 intended to cooperate with the rails 423 and a nut (not shown) intended to cooperate with the screw -mother 424 so that the seat 43 for translational movement of the Y axis moves in translation on the rails 423 parallel to the Y axis when the lead screw 424 is rotated by a

servomotor (not shown).

  As shown in Figures 2, 3 and 4, in the vertical direction of axis Z, as the lead screw 22 has a section 221 of positive pitch and a section 222 of reverse pitch

  intended to cooperate with the nuts 412 and 312 respec-

  tively fixed to the tool holder assembly 4 and the machine table assembly 3, the machine table assembly 3 and the tool holder assembly 4 move simultaneously in opposite directions along the axis Z to get closer (see figure 3) or to move away (see figure 4), when the lead screw 22 is turned clockwise (see figure 3) or counterclockwise (see figure 4) by the servomotor Ml, so that the relative speed of movement along the Z axis between the assembly 3 at the working table and the assembly 4 with the tool holder is twice the speed of displacement in the conventional machine shown in Figure 1 having a lead screw R of one direction not having a nut N for moving the tool holder relative to the workpiece. Even if the servomotor does not increase the speed of rotation of the lead screw, the relative speed of movement between the tool holder assembly and the machining table assembly along at least one axis, according to the invention , is double the speed conventionally obtained when using a single-pitch lead screw associated with a

  nut fixed to the tool holder or the machining table.

  In the direction of the X axis, when the servomotors M21 and M22 rotate the lead screws 414 and 314 respectively at a single step simultaneously, the upper seat 41 of the X axis and the working table 32 move simultaneously in the opposite direction. opposite along the X axis, so that the relative speed of movement of the tool holder and the machining table along the X axis also increases to a double value, compared to the conventional device which simply moves the door -tool

or the machining table.

  In the direction of the Y axis, as the distance required to move the tool in this direction is very small, the operation of moving the tool holder in the direction of the Y axis can be carried out simply in a conventional manner by use of the lead screw 424 with a single step driven in rotation by a servomotor (not shown) associated with a nut (not shown) fixed to the seat 43 for displacement in translation of the Y axis. Like the lead screw 22 placed vertically along the axis Z and which can turn to a section 224 with positive pitch and a section 222 with reverse pitch intended to cooperate respectively with the nuts 412 and 312 fixed to the tool holder assembly 4 and the table assembly d machining 3, if the weight of the machining table assembly 3 is practically equivalent to the total weight of the tool holder assembly 4, the torque created by the weight of the machining table assembly 3 which rotates the lead screw 22 in one direction is compensated o u neutralized by the opposing torque created by the weight of the tool holder assembly 4 which tends to rotate the vismere 22 in the other direction. Consequently, the loads of the servomotor M1 when it turns the lead screw 22 in one direction and in the other are practically identical, and it is therefore not necessary to use an additional counterweight to reduce the difference in load. of the servomotor when it moves the vertical lead screw in a

one way or the other.

  During the operation of the machining center,

  that a workpiece is placed on the machining table 32, if the

  machining center unexpectedly experiences a power failure

  tation, since the total weight of the table assembly

  3 and the workpiece is slightly greater than the total weight of the tool holder assembly 4, the machining table assembly 3 descends slowly and creates a torque intended to rotate the lead screw 22 and to move the toolholder assembly 4 slowly upwards. Consequently, the tool fixed on the tool holder assembly 4 never collides with the part placed on the machining table assembly 3 when the machining center is stopped or undergoes

  inadvertent power interruption.

  FIG. 5 represents a second preferred embodiment of a numerically controlled machining center according to

  the invention. The construction of this second embodiment

  tion is similar to that of the first shown in Figure 2, described above. In particular, the constructions intended to ensure the relative operations of displacement of the assembly 4 with tool holder and of the assembly 3 with machining table along the axes Z and Y respectively are practically the same as those of the first mode of embodiment shown in Figure 2. The first embodiment shown in Figure 2 provides the relative movement of the machining table assembly 3 and the tool holder assembly 4 along the axis X to using two servomotors M21 and M22 which rotate separately and simultaneously two lead screws with a single step 414 and 314. On the contrary, the second embodiment performs the operation of relative displacement of the table assembly. machining 3 and the tool holder assembly 4 along the X axis thanks to the lead screw having opposite steps and driven by a servomotor, like the lead screw 22 of Figures 2 and 3, so that the two nuts fixed to the machining table 32 and to the seat upper 42 of X axis cooperate. In particular, the second embodiment of a numerically controlled machining center shown in FIG. 5 comprises a lead screw 5 which has two opposite sections of pitch, like the lead screw 22 in FIGS. 2 and 3. The screw mother 5 comprising a positive step section 51 and a reverse step section 51 is rotatably mounted on the base

  vertical 2 along the X axis and is driven by the servo

  M5 motor so that it turns in one direction and in the other.

  In cooperation with the section 51 of positive pitch and the section 52 of reverse pitch of the lead screw 5, the tool holder assembly 4 and the machining table assembly 3 respectively comprise a nut 53 and a nut 54 fixed on rails 55 and 56 arranged along the Z axis. The working table 32 is formed along the Z axis with a slide 322 which allows the insertion of the rail 56 and which can slide along the Z axis along of the rail 56. As in the case of the slide 322 of the machining table 32, the upper seat 42 of axis X is formed with a sliding groove (not shown) arranged along the axis Z and allowing the insertion of the rail and sliding parallel to the Z axis. Consequently, two nuts 53 and 54 are moved simultaneously in opposite directions on the mother screw 5, parallel to the X axis, when the servomotor M5 rotates the vismere 5, so as the nuts move closer or further apart. Thanks to the transmission using rails 55 and 56, the upper seat 42 of axis X and the machining table 32 are moved simultaneously in direction

  opposite along the X axis to approach or move away.

  Figure 6 shows a machining center with control

  digital according to the invention in a third embodiment

  tion. The constructions of this third embodiment are practically the same as those of the second embodiment shown in FIG. 5, but the nuts 53 and 54 of the third embodiment are produced respectively on a slide 55 'and a slide 56' intended to cooperate by sliding with a rail 425 parallel to the axis Z from the upper seat of axis X 42 and a rail 322 'parallel to the axis Z from the machining table 32. Thanks to the transmission of energy by the slides 53 and 54 which cooperate by sliding with the rails 425 and 322 ', the upper seat 42 of axis X and the machining table 32 are moved simultaneously in opposite directions along the axis X, when the servomotor M5 rotates the lead screw 5 to drive the nuts 53 and 54 while simultaneously moving them in opposite directions along the axis X. In the preferred embodiments described

  previously, those skilled in the art may note that the screw

  mother 22 which has two opposite pitch sections 221 and 222 as indicated in FIGS. 3 and 4 can also be arranged so that it can pivot in a horizontal spindle direction by a horizontal lathe or by a horizontal machining center (not shown) for the simultaneous drive of a tool holder and a machining table intended to move in opposite directions in the direction of the spindle, so that the relative movement of the tool holder and the

machining table can be increased.

  Of course, various modifications can be made by those skilled in the art to the machining centers which have just been described solely by way of non-illustrative example.

  limiting without departing from the scope of the invention.

Claims (14)

  1. Machining center with numerical control, having a capacity of displacement at double speed along axes X and Z, characterized in that it comprises: a foundation (1) of support of frame, a base (2) of support projecting from the foundation (1) along a first axis of coordinates, a first lead screw (22) having two sections of opposite steps, that is to say a section (221) of positive step and a   section (222) of reverse pitch, and arranged in a rota   tive on the vertical base (2) along the first coordinate axis, an assembly (3) with a machining table arranged so that it can move alternately on the support base (2) along the first coordinate axis and comprising a first nut (312) cooperating with the reverse pitch section of the first lead screw (22) so that the table assembly (3) moves alternately along the first coordinate axis in a direction of displacement when the first vismere (22) rotates in a first direction, and a tool holder assembly (4) arranged so that it moves in translation on the support base (2) along the first coordinate axis and comprising a second nut (412) cooperating with the positive pitch section of the first lead screw (22) so that the tool holder assembly (4) moves in translation along the first coordinate axis in the opposite direction to the direction displacement of   the assembly (3) at the machining table when the first screw   mother (22) is rotated.   2. Center according to claim 1, characterized in that the base (2) for support is a vertical base arranged above the foundation (1) for frame support along the first axis of coordinates perpendicular to the foundation (1) frame support.   3. Center according to claim 1, characterized in that the base (2) for support is disposed horizontally on the foundation (1) for support of frame along the first axis coordinates.   4. Center according to claim 2, characterized in that the assembly (3) to the machining table further comprises a lower seat (31) of axis Z and a machining table, in which the lower seat (31 ) Z axis cooperates with the reverse pitch section of the first lead screw (22) using the first nut (312), and the work table cooperates with the lower seat (31) Z axis and is movable relative to the lower seat (31) of Z axis along a second axis of   coordinates perpendicular to the first coordinate axis.   5. Center according to claim 4, characterized in that the lower seat (31) of the Z axis comprises a second lead screw (314) arranged so that it can rotate along a second axis of coordinates, and the table machining involves   in addition a third nut which cooperates with the second screw-   mother (314) so that the machining table is moved in translation along the second mother screw (314) and following the second coordinate axis.   6. Center according to claim 2, characterized in that the assembly (4) with tool holder comprises an upper seat (41) of axis Z, an upper seat (42) of axis X and a seat (43) of displacement in translation of axis Y, and the upper seat (41) of axis Z cooperates with the positive pitch section of the first lead screw (22) using the second nut (412), the upper seat (42) of axis X cooperates with the upper seat (41) of axis Z and is movable relative to the upper seat (41) of axis Z along a second coordinate axis perpendicular to the first coordinate axis, and the seat (43) of movement in translation of axis Y which cooperates with the upper seat (42) of axis X is movable relative to the upper seat (42) of axis X along a third axis of coordinates perpendicular to the first and second coordinate axes.   7. Center according to claim 6, characterized in that the upper seat (41) of the Z axis comprises a third lead screw (414) arranged so that it rotates along the second coordinate axis, and the upper seat ( 42) of axis X has a fourth nut cooperating with the third lead screw   (414) and intended to move the upper seat in translation   X axis (42) along the third lead screw (414) and   along the second coordinate axis.   8. Center according to claim 6, characterized in that the upper seat (42) of axis X comprises a fourth lead screw (424) arranged so that it rotates along the   third coordinate axis, and the seat (43) of displacement   cement in translation of axis Y has a fifth nut cooperating with the fourth mother screw (424) and intended to move in translation the seat (43) of displacement in translation of axis Y placed along the fourth mother screw ( 424) and the   along the third coordinate axis.   9. Center according to claim 4, characterized in that it further comprises a fifth lead screw having two parts of opposite pitches, a positive pitch section and a reverse pitch section, and arranged in a rotary manner on   the vertical base (2) along the second coordinate axis.   10. Center according to claim 6, characterized in that it further comprises a fifth lead screw having two opposite step sections, a positive step section and a reverse step section, and arranged so that it rotates on   the vertical base (2) along the second coordinate axis.   11. Center according to claim 9, characterized in that the machining table has a sixth nut cooperating with the reverse pitch section of the fifth lead screw so that the machining table is moved in translation along the fifth mother screw and along the second coordinate axis   during the displacement by rotation of the fifth lead screw.   12. Center according to claim 10, characterized in that the machining table has a sixth nut cooperating with the reverse pitch section of the fifth lead screw so that the machining table is moved in translation along the fifth lead screw and along the second coordinate axis when the fifth lead screw is rotated. 13. Center according to claim 11, characterized in that the upper seat (42) of axis X comprises a seventh nut cooperating with the positive pitch section of the   fifth mother screw so that it causes an alter-   native of the upper seat (42) of axis X along the fifth lead screw and along the second coordinate axis in a movement operation in the direction opposite to the direction of movement of the working table due to the rotation of the fifth screw.   14. Center according to claim 12, characterized in that the upper seat (42) of axis X comprises a seventh nut cooperating with the positive pitch section of the   fifth mother screw so that it causes an alter-   native of the upper seat (42) of axis X along the fifth lead screw and along the second coordinate axis in a movement operation in the direction opposite to the direction of movement of the working table due to the rotation of the fifth screw.