DE20021675U1 - CNC machine with increased infeed speed in the X and Y directions - Google Patents

Description

CNC machine with increased feed speed in X and Y directions

The invention relates to a computer-controlled numerical control machine tool (CNC machine), in particular to a CNC machine with a threaded rod arrangement with a positive threaded portion and a counter-threaded portion and two nuts, each of which is fastened to a tool holder arrangement and a tool table arrangement, which are simultaneously moved in opposite directions with respect to each other along at least one coordinate axis in order to increase the relative movement speed of the tool holder arrangement and the work table to each other, which can significantly reduce the delivery times of a CNC machine.

reduces.

Usually, a CNC machine that machines a workpiece using a tool is equipped with devices that move the tool to the workpiece during a work step; a CNC machine also contains devices to change and readjust the relative position between the tool and the workpiece during an interruption of the machining process. During the machining process, the feed rate of the tool relative to the workpiece is determined by the material properties of the material to be machined and should not be changed or arbitrarily increased. However, if the feed time between the workpiece and the tool can be shortened during the interruption of the machining process, efficiency and productivity can be significantly increased by increasing the machining speed of workpieces by the CNC machine.

30 can be increased.

The illustration in Figure 1 shows a conventional CNC machine in use today, which comprises a work table T, which is connected to a movable carriage Tl via a screw connection (not shown).

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spindle R, the work table T can be moved along the X-axis on the sliding carriage Tl when the threaded spindle R is rotated by means of a drive M. The sliding carriage Tl is connected to the machine bed F via an additional threaded spindle mechanism so that it can be moved in the Y direction on the machine bed F. Similarly, a tool holder B is mounted on an upright column FV by means of a threaded spindle R and a nut N so that the tool holder B can be moved up and down along the Z-axis on the upright column. This allows the relative positions in three coordinate directions between the tool holder B and the work table T to be adjusted in order to simplify workpiece machining.

With respect to the conventional application of using a lead screw/nut mechanism, i.e. a gear mechanism with a screw pair consisting of a lead screw and a nut as shown in Figure 1, to change the relative positions between the tool holder and the work table and to increase the speed at which the tool holder approaches or moves away from the work table, only the rotation speed of the lead screw can be increased by using a servo motor with a higher output speed. However, it has been found that none of the servo motors available on the market satisfactorily meets this requirement so that a satisfactory speed of displacement between the tool holder and the work table can be achieved during an interruption of the cutting operation.

In particular, in the case of conventional threaded spindle/nut mechanisms where translational movements of the tool holder along a vertical axis are required, i.e. when the tool holder N is moved along the vertical Z-axis by the threaded spindle R in conjunction with the nut N of a conventional CNC machine, as shown in Figure 1, the load on the servo motor M for rotating the threaded spindle R for upward movements of the tool holder B is considerably greater than the load on the servo motor for downward movements of the tool holder B. This is due to the weight of the tool holder B. This circumstance not only reduces the service life of the tool holder used, but also reduces the tool life of the tool holder.

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servo motor, but is disadvantageous in terms of controlling the machining speed. In order to remedy this problem of uneven loading of a servo motor M during the up and down movement of the tool holder B, when driving the threaded spindle for the downward and upward movements of the tool holder B, chains, wires or the like are usually used to move a counterweight. The counterweight usually corresponds to the weight of the tool holder B, so that the problem of the different loading of the servo motor during the upward and downward movement of the tool holder can be avoided. Although this approach represents a viable way, it has the disadvantage that it makes the machine tool structurally complicated, more bulky and is disadvantageous in terms of its manufacture and maintenance.

With respect to the conventional CNC machine shown in Fig. 1, the tool holder B is moved up or down when the servo motor M drives the lead screw R clockwise or counterclockwise. With such an operating method and design of a servo motor M in combination with a lead screw/nut mechanism for moving a tool holder B up or down, the weight of the tool holder B generates a moment to twist the freely rotating lead screw R when the servo motor M is stopped or when the electric power is turned off, so that the tool holder B gradually moves down. This will inevitably cause the tool holder B to collide with a clamped workpiece, the work table T or other parts of the machine tool.

Therefore, it is an object of the present invention to provide a CNC machine in which the relative displacement speed along at least one coordinate axis between the tool and the workpiece is at least twice the relative displacement speed of conventional CNC machines which also use lead screw/nut gears to move either only the tool or only the work table. According to the present invention, the lead screw comprises two sections with opposite thread pitches, namely a positive thread pitch and a counter thread pitch, which cooperate with two nuts which are separately received on the tool holder assembly and on the work table assembly, respectively, to achieve a relative displacement between the

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tool and the workpiece so that the interruption of the machining processes by feed movements on the CNC machine can be significantly reduced and the overall machining speed and productivity can be improved.

Another object of the present invention is to provide a CNC machine in which the tool holder assembly and the work table assembly can be moved translationally along a vertical axis by means of a threaded spindle having two sections of different thread pitches, namely a positive thread pitch and a counter thread pitch, which cooperate with two nuts which are received either on the tool holder assembly or on the work table assembly. In this way, a servo motor can be operated with essentially identical load when driving the threaded spindle clockwise or counterclockwise to change the relative position along the vertical axis between the tool holder assembly and the work table assembly, so that an additional counterweight can be omitted.

Another object of the present invention is to provide a CNC machine which ensures that in the event of an unexpected power failure or a switched off servo drive, no collisions can occur between tool holders and clamped workpieces or parts of the machine.

Further advantageous properties, operating principles, advantages, construction variants and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which identical reference numerals designate identical components.

drawing

Figure 1 shows a schematic perspective view of a

conventional CNC machine, where the work table and the tool holder are positioned relative to each other along the X, Y and Z axes

are movable,

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Figure 2 shows a schematic, perspective view of a

first advantageous embodiment of a CNC machine according to the present invention, wherein the relative movement between the

Work table and the tool holder along a vertical axis (Z-

Axis) via a threaded spindle with positive thread pitch

and a counter thread section, each with

a screw attached to the workbench or tool holder so that the workbench and the tool holder

along the vertical Z-axis at double speed relative

are adjustable to each other,

Figure 3 shows a schematic view of the threaded spindle according to the

present invention, which has a positive threaded portion and

comprises a counter-threaded section, each of which works together with two screws on the work table and the tool holder, whereby the threaded spindle rotates clockwise so that the work table and the tool holder are moved towards each other,
20

Figure 4 shows another schematic view of the

Threaded spindle according to the present invention, wherein the threaded spindle rotates counterclockwise so that the work table and the tool holder are spaced apart,
25

Figure 5 shows a schematic perspective view of a CNC machine in

According to a second preferred embodiment of the present invention and

Figure 6 shows a schematic perspective view of a

CNC machine in accordance with a third preferred embodiment of the present invention.

Before the individual embodiments of the solution proposed according to the invention are described in more detail, it should be pointed out that certain terms in the

The terms "forward," "backward," "right," "left," "upper," and "lower" are used to indicate directions in the respective drawings to which reference is made. The terms "inward," "inside," or "inside," and "outside," "outer," and the like refer to directions either toward or away from the center of the element being referred to. The terms "radial" and "axial" refer to directions or planes circumferentially and parallel to the longitudinal axis of the element being referred to. Similar terminology other than those used above is not intended to be limiting, but is chosen for the sake of simplicity.

For ease of description, X, Y and Z axes are mentioned below and refer to the three coordinate axes that are perpendicular to each other and indicated in the accompanying drawings. Identical reference numerals identify identical components in the accompanying drawings.

As can be seen from the illustration in Figure 2, a CNC machine according to a first preferred embodiment of the present invention includes a machine bed 1, an upright column 2, a work table assembly 3 and a tool holder assembly 4. The upright column 2 extends vertically to the machine bed 1 and includes two upwardly facing rails 21 arranged parallel to each other. With reference to Figures 2 and 3, a lead screw 22 includes two portions of opposite thread pitches, namely a positive thread portion 221 and a counter thread portion 222. The lead screw 22 is rotatably received in the upright column 2 along the vertically extending Z-axis and is driven by a servo motor M1 either clockwise or counterclockwise.

The work table arrangement 3, provided for receiving and fixing a workpiece to be machined, comprises a Z-axis slide 31 and a work table 32, wherein the Z-axis slide 31 contains two sliding pieces 311, which cooperate with the rails 21 for guiding the Z-axis slide 31, so that a translatory

Movement downwards and upwards along the Z-axis in the upright stand 2 is made possible. A nut 312 is attached to the Z-axis slide 31 and encloses the counter-threaded section 222 of the threaded spindle 22 to enable a translational movement of the Z-axis slide 31 along the Z-axis when the threaded spindle 22 is rotated by means of the servo motor M1. The Z-axis slide 31 is provided in the X-direction with two mutually parallel rails 313 and a threaded spindle 314 which is rotatably received in the X-axis slide 31 and is driven by means of a servo motor M22.

The work table 32 contains two sliding elements 321 which move on the rails 313 by means of a nut (not shown here), which in turn cooperates with the threaded spindle 314, so that the work table 32 can be moved in a translational direction on the rails 313 in the X direction when the servo motor M22 drives the threaded spindle 314.

The tool holder assembly 4 includes a Z-axis slide 41, an X-axis slide 42 and a Y-axis slide 43. The Z-axis slide 41 is provided, similar to the Z-axis slide 31 as described above, with two sliding elements 411 which cooperate with the rails 21; furthermore with a nut 412 which encloses the positive threaded portion 221 of the threaded spindle 22, so that the Z-axis slide 42 can be moved up or down along the Z-axis when the threaded spindle 22 is rotated via the servo motor M1. The Z-axis slide 41 comprises parallel rails 413 extending along the X-axis and a threaded spindle 414 which is rotatably received in the X-axis slide 41 along the X-axis and can be driven by a servo motor M21.

The X-axis slide 42 comprises two parallel sliding elements 421, which cooperate with the rails 413 and a nut (not shown), which in turn encloses the threaded spindle 414, so that the X-axis slide 42 can be moved translationally along the rails 413 in the direction of the X-axis when the threaded spindle 414 is rotated via the servo motor M21. The X-axis slide 42 is further provided in the Y-direction with two parallel rails 423 and a threaded spindle 424, which is rotatable in the X-axis upper seat 42 in the Y-direction.

extending and can be driven by a servo motor not shown here in detail.
5

The Y-axis sliding carriage 43 is suitable for receiving a tool spindle (without reference number) and comprises two sliding elements 431 which cooperate with the rails 423 and a nut (not shown here), which in turn encloses the threaded spindle 424, so that the Y-axis sliding carriage 43 can be moved back and forth on the rails 423 in the Y direction when the threaded spindle 424 is driven by the servo motor (not shown).

As preferably shown in Figures 2, 3 and 4, the work table assembly 3 and the tool holder assembly 4 move simultaneously in two opposite directions along the Z-axis to move closer to or away from each other when the lead screw 22 is rotated clockwise (see Figure 3) or when the lead screw is driven counterclockwise (see Figure 4) by the servo motor M1. The opposing movements are produced by the lead screw 22 which comprises a positive threaded portion 221 and a counter threaded portion 222 which are respectively engaged with the nuts 412 and 312 received on the tool holder assembly 4 and on the work table assembly 3. As a result, the relative displacement speeds along the Z axis between the work table assembly 3 and the tool holder assembly 4 are twice the displacement speed of a conventional machine tool shown in Figure 1, in which a threaded spindle R is incorporated with a single threaded portion which cooperates with a nut N to displace the tool holder B relative to the workpiece. Notwithstanding the increase in the rotational speed of the threaded spindle by the servo motor, the solution proposed by the invention offers the possibility of doubling the relative displacement speed between the tool holder assembly and the workpiece table in at least one axis, compared to the conventional speeds in a machine tool which employs a threaded spindle with a single thread pitch in cooperation with a nut incorporated on the tool holder or on the work table.

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In the X-axis direction, when the servo motors M21 and M22 drive the single-threaded lead screws 414 and 314, respectively, the X-axis slide 41 and the work table 32 simultaneously move in opposite directions to each other along the X-axis, so that the relative displacement speed between the tool holder and the work table along the X-axis is increased to twice that of the conventional way of displacing either only the tool holder or only the tool table.

Since the movement distance for the tool is relatively short with respect to the Y-axis, the displacement operation for the tool holder in the Y direction can be accomplished very easily by moving a single-threaded lead screw 424 by a servo motor (not shown) which cooperates with a nut (not shown) which is attached to the Y-axis slide 43.

Since the threaded spindle 22, which is received vertically and rotatably in the Z direction, comprises the positive threaded section 221 and the counter-threaded section 222, which interact with the nuts 412 and 312, respectively, which are located on the tool holder arrangement 4 and on the work table arrangement 3, respectively, the weight of the work table arrangement 3, if this substantially corresponds to the total weight of the tool holder arrangement 4, can be balanced. The moment which is generated by the weight of the work table arrangement 3 and which rotates the threaded spindle 22 in one direction is balanced or neutralized by a counter-moment which is exerted by the tool holder arrangement 4 on the threaded spindle 22 in its other direction of rotation. As a result, the loads which the servo motor M1 has to apply to rotate the threaded spindle clockwise or counterclockwise substantially correspond to one another. Therefore, it is no longer necessary to provide an additional counterweight to minimize the load difference for the servo motor to drive the vertically extending lead screw clockwise or counterclockwise.

If during operation of the CNC machine, when a workpiece is placed on the tool table 32, the CNC machine is suddenly switched off and the total weight of the work table assembly 3 and the workpiece is slightly higher than the

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total weight of the tool holder assembly 4, the work table assembly 3 will slowly move downward and create a moment which twists the lead screw 22 and slowly moves the tool holder assembly 4 upward. As a result, the tool held on the tool holder assembly 4 will not collide with the workpiece held on the work table assembly 3 when the CNC machine is turned off or unexpectedly stopped.

A second preferred embodiment of a CNC machine according to the present invention can be seen in the illustration according to Figure 5. The design of the second embodiment is similar to the design of the first embodiment according to Figure 2, as already described above. In particular, the devices which are designed in the second embodiment to bring about a relative displacement operation between the tool holder arrangement 4 and the work table arrangement 3 along the Z and Y axes, respectively, are essentially identical to the corresponding devices which are shown in the first embodiment in connection with Figure 2. In the first embodiment according to Figure 2, the relative displacement operation of the work table arrangement 3 and the tool holder arrangement 4 along the X axis is achieved by means of two servo motors M21 and M22 simultaneously and separately by two individual threaded spindles 414 and 314 provided with threaded sections. In contrast, in the second embodiment according to the present invention, the relative displacement operation between the work table assembly 3 and the tool holder assembly 4 along the X-axis is realized via a threaded spindle which comprises opposing threaded portions and is driven by a servo motor, similar to the threaded spindle 22 as shown in Figures 2 and 3. The threaded spindle 22 cooperates with two nuts which are received on both the work table 32 and the X-axis slide 42.

In particular, the second embodiment of the CNC machine as shown in Figure 5 comprises a threaded spindle 5 which comprises two sections with two opposing threads, similar to the threaded spindle 22 as shown in Figures 2 and 3. The threaded spindle 5 comprises a positive threaded section 51 and a counter threaded section 52 which are rotatably mounted on the upright 2 in the X-axis direction and which are rotated clockwise by a servo motor M5.

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or counterclockwise. Cooperating with the male threaded portion 51 and the female threaded portion 52 of the lead screw 5, respectively, the tool holder assembly 4 and the work table assembly 3 each include a nut 53 and a nut 54 received on rails 55 and 56, respectively, each extending in the Z-axis direction. The work table 32 extends in the Z-axis direction with an opening 322 through which the rail 56 extends and allows sliding along the rail 46 in the Z-axis. Similar to the opening 322 of the work table 32, the X-axis carriage 42 in the Z direction includes a sliding recess (not shown) through which the rail 55 extends and allows sliding movement in the Z-axis direction. In this way, when the servo motor M5 drives the screw spindle 5, two nuts 53 and 54 are simultaneously moved in opposite directions on the screw spindle 5 in the X-axis direction, so that the nuts 53 and 54 are moved toward each other or away from each other depending on the direction of rotation. By interposing the rails 55 and 56, the X-axis slide 42 and the work table 32 are simultaneously moved in opposite directions along the X-axis to move toward each other or away from each other.

A third embodiment of the CNC machine according to the present invention is shown in Figure 6. The construction variant according to the third embodiment is essentially identical to the second embodiment according to the illustration in Figure 5, except that the nuts 53 and 54 of the third embodiment are provided with sliding elements 55' and 56' respectively in order to enable a sliding movement along a rail 425 along the Z-axis and the X-axis sliding carriage 43 and along the sliding rail 322' along the Z-axis of the work table 32. By transmitting motion by means of the sliding element 55' or 56', which slide on the rails 425 or 322', the X-axis carriage 42 and the work table 32 are moved simultaneously in opposite directions along the X-axis when the servo motor M5 drives the threaded spindle 5, so that the nuts 53 or 54 are moved simultaneously in opposite directions along the X-axis.

Claims (9)

1. CNC machine with speed doubling when moving along the X and Z axes with the following features: - a machine bed ( 1 ), - a column ( 2 ) oriented in an upright arrangement, which extends upwards from the machine bed ( 1 ) along a first coordinate axis (Z-axis), - a first threaded spindle ( 22 ) which comprises two sections of opposing threads, namely a positive thread section ( 221 ) and a counter thread section ( 222 ) and is rotatably received in the upright stand ( 2 ) along the first coordinate axis, - a work table arrangement ( 3 ) which can be moved back and forth on the upright stand ( 2 ) along the first coordinate axis, wherein a first nut ( 312 ) encloses the counter-threaded section ( 222 ) of the first threaded spindle ( 22 ) for the translational movement of the work table arrangement ( 3 ) along the first coordinate axis in a displacement direction when the first threaded spindle ( 22 ) is rotated in a first direction, - a tool holder assembly ( 4 ) received on the upright ( 2 ) along the first coordinate axis and reciprocating thereon, with a second nut ( 412 ) enclosing the positive threaded portion ( 221 ) of the first threaded spindle ( 22 ) to reciprocate the tool holder assembly ( 4 ) along the first coordinate axis in a direction opposite to the direction of displacement of the work table assembly ( 3 ) when the first threaded spindle ( 22 ) is rotated. 2. CNC machine according to claim 1, characterized in that the work table arrangement ( 3 ) comprises a Z-axis slide ( 31 ) and a work table ( 32 ), the Z-axis slide ( 31 ) enclosing the counter-threaded section ( 222 ) of the first threaded spindle ( 22 ) by means of a first nut ( 312 ) and the work table ( 32 ) enclosing the Z-axis slide ( 31 ) and being movable relative to the Z-axis slide ( 31 ) along a second coordinate axis perpendicular to the first coordinate axis. 3. CNC machine according to claim 2, characterized in that the Z-axis carriage ( 31 ) comprises a second threaded spindle ( 314 ) which is rotatable about the second coordinate axis and the work table ( 32 ) further comprises a third nut which encloses the second threaded spindle ( 314 ) in order to move the work table ( 32 ) back and forth along the second threaded spindle ( 314 ) in the direction of the second coordinate axis. 4. CNC machine according to claim 1, characterized in that the tool holder arrangement ( 4 ) comprises a Z-axis slide ( 41 ), an X-axis slide ( 42 ) and a Y-axis sliding slide ( 43 ), the Z-axis slide ( 41 ) enclosing the positive threaded portion ( 221 ) of the first threaded spindle ( 22 ) by means of a second nut ( 412 ), while the X-axis slide ( 42 ) is movable relative to the Z-axis slide ( 41 ) along a second coordinate axis perpendicular to the first coordinate axis and the Y-axis sliding slide ( 43 ) is movable relative to the X-axis slide ( 42 ) along a third coordinate axis perpendicular to the first and second coordinate axes. 5. CNC machine according to claim 4, characterized in that the X-axis slide ( 42 ) comprises a third threaded spindle ( 424 ) which is rotatably received along the second coordinate axis and the X-axis slide contains a fourth nut which encloses the third threaded spindle ( 424 ), with which the X-axis slide ( 42 ) can be moved back and forth along the third threaded spindle ( 424 ) and in the direction of the second coordinate axis. 6. CNC machine according to claim 4, characterized in that the X-axis slide ( 42 ) comprises a fourth threaded spindle which is rotatably received along a third coordinate axis and the Y-axis sliding slide ( 43 ) comprises a fifth nut which encloses the fourth threaded spindle, with which the Y-axis sliding slide ( 43 ) is movable along the fourth threaded spindle and along the third coordinate axis. 7. CNC machine according to claim 2 or 4, characterized in that it comprises a fifth threaded spindle ( 5 ) which comprises two threaded sections running in opposite directions, namely a positive threaded section ( 51 ) and a counter threaded section ( 52 ) and is rotatably mounted on the upright ( 2 ) along the second coordinate axis (X-axis). 8. CNC machine according to claim 7, characterized in that the work table arrangement ( 3 ) includes a sixth nut ( 54 ) which encloses the counter threaded portion ( 52 ) of the fifth threaded spindle ( 5 ) in order to displace the work table ( 32 ) back and forth along the fifth threaded spindle ( 5 ) in the direction of the second coordinate axis when the fifth threaded spindle ( 5 ) is set in rotation. 9. CNC machine according to claim 8, characterized in that the X-axis slide ( 42 ) comprises a seventh nut ( 53 ) which encloses the positive threaded portion ( 51 ) of the fifth threaded spindle ( 5 ) for moving the X-axis slide ( 42 ) along the fifth threaded spindle ( 5 ) in the direction of the second coordinate axis such that a direction of displacement opposite to the direction of displacement of the work table ( 32 ) is achieved during rotation of the fifth threaded spindle ( 5 ).