EP1140423A2

EP1140423A2 - Machine tool with a piezoelectric position adjusting device

Info

Publication number: EP1140423A2
Application number: EP99964391A
Authority: EP
Inventors: Dieter Kroll; Stefan Weber
Original assignee: Schwaebische Werkzeugmaschinen GmbH
Current assignee: Schwaebische Werkzeugmaschinen GmbH
Priority date: 1998-12-22
Filing date: 1999-12-03
Publication date: 2001-10-10
Also published as: WO2000037213A3; WO2000037213B1; DE19859360A1; WO2000037213A2; DE19859360C2

Abstract

The invention relates to a machine tool (1) especially for machining work pieces. Said machine tool comprises a machining unit (3). At least one electrically controlled piezoelectric control element (11) is provided as a position adjusting device, especially for a work spindle (4) of the machining unit (3). If a change of position is detected, the machining unit can quickly be mechanically moved to the respective desired position.

Description

Machine tool with piezoelectric position correction device

The invention relates to a machine tool for in particular machining workpieces, with a processing unit and / or a workpiece table and with a position correction device for the processing unit or the workpiece table. Such a machine tool has become known, for example, from DE 196 07 599 AI.

In order to avoid machining inaccuracies in this known machine tool due to thermally induced changes in the position of the workpiece and / or tool in the working area of the tool, stationary optical measuring barriers are provided, through which the workpiece and tool are moved simultaneously or in quick succession. The positions thus detected are compared to stored positions from previous measurements, and the difference between the detected and previously measured positions is used to correct the machine control. This means that the tool or workpiece is not mechanically moved back to the setpoint, but the change in position is taken into account by a corresponding correction of the setpoints of the machine control. In addition, dynamic position correction during the machining of a workpiece is not possible.

In contrast, it is the object of the invention to develop a machine tool of the type mentioned at the outset in such a way that when a change in position is detected, the machining unit and / or the workpiece table can be mechanically moved as quickly as possible into its respective desired position.

This object is achieved in that at least one electrically controlled piezoelectric (piezoceramic) actuating element is provided as the position correction device, in particular for a work spindle of the processing unit. Piezoelectric control elements (actuators), with which stretches of up to approx. 300 Im can be achieved today, have very high rigidity and in particular very short actuation times (less than 1 ϊs). In machine tools they can be used on both the tool and the workpiece side, for example:

- to compensate for thermal deformations and displacements;

- to compensate for geometrical position errors (e.g. the workpieces);

- to compensate for deformations and displacements due to acting forces;

- to compensate for tool size fluctuations (e.g. tool length correction, especially a relative tool length correction in multi-spindle systems);

- for active vibration damping.

For example, the work spindles of machine tools, in particular multi-spindle machines, can be coupled to the machine tool in a spatially displaceable manner with the aid of piezoelectric adjusting elements. This enables a spatial movement of the or each individual work spindle that is superimposed on the degrees of freedom of the conventional machine axes. The machine stand, for example a slide unit, with the work spindle carries out the axis movements specified by the control program, while a work spindle can also carry out superimposed compensation movements for a position correction. This piezoelectric position correction device according to the invention can be used both in conventional work spindles and in motor spindles and multi-spindle drilling heads. To adjust position errors between tool and workpiece, which arise due to the above-mentioned influences, the work spindle can either be controlled to a target position by means of predefined parameters, or the tool or work spindle position is adjusted to the workpiece or with the help of a closed control loop. Adjusted target position. The target / actual deviation can be determined by means of mechanical, optical, capacitive or inductive sensors or buttons. The dimensions can be adjusted both on the workpieces to be machined and on the tool.

The deviation is then determined in several control steps, e.g. minimized by moving the work spindle to its target position. In the case of the controlled procedure, the work spindle is controlled into its exact target position on the basis of parameters typical of the machine, tool or device. These parameters can also be variably based on the respective machine condition (temperature, machining force, etc.).

In preferred embodiments of the invention, the effective direction of the at least one piezoelectric actuating element runs approximately in the direction of a linear degree of freedom of the machining unit or the workpiece table, i.e. in the direction of the conventional machine axes X, Y or Z. In addition to thermally induced displacements, tool dimension fluctuations, for example the tool length or Tool setting dimensions can be changed. This enables an individual and separate adjustment of each individual work spindle in the Z direction, in particular in the case of multi-spindle systems in which it is otherwise not possible to compensate their work spindles in the axial direction (Z direction) with respect to one another. In an advantageous development of this embodiment, each linear degree of freedom of the processing unit or the workpiece table can be assigned at least one piezoelectric actuating element. This measure allows any spatial position correction, for example of the work spindle (s), to be carried out.

In another embodiment of the invention, the effective direction of the at least one piezoelectric actuating element extends approximately radially to a linear degree of freedom of the processing unit or the workpiece table. This embodiment has the essential advantage that e.g. a work spindle can be moved via the at least one piezoelectric actuating element from its position parallel to a linear degree of freedom (Z direction), in particular can be shifted in parallel or tilted.

For this purpose, in an advantageous development of this embodiment, the machining unit or the workpiece table can be spatially adjustable in a spatially adjustable manner by means of a multi-point holder formed by at least two, preferably at least three piezoelectric adjusting elements. The adjusting elements are to be provided at the same angular intervals on the processing unit or the workpiece table.

Furthermore, it is particularly advantageous in this development if the processing unit or the workpiece table is mounted in spatially adjustable manner via at least two multi-point holders arranged one behind the other in the direction of the linear degree of freedom. With two multi-point brackets, for example with three control elements arranged under 120 in two radial planes, a work spindle can be moved in the radial planes spanned by the three control elements. adjust dial, either parallel to the spindle axis or spherical. In the latter case, the axis direction of the work spindle or the workpiece clamped therein changes. The spherical adjustability of the work spindle can also compensate for wobble errors in the work spindle. It also makes it possible to compensate for accuracy-related, geometric deviations of the machine tool and errors due to the flexibility of the machine structure.

Depending on the position of the center of mass of a movable machining unit, in particular its slide unit, the forces or loads acting on its guide change during machining. This results in geometry deviations depending on the respective position of the slide. In the worst case, this load can cause the sled to tip over. In order to be able to compensate for such forces depending on the position of the slide, the at least one piezoelectric actuating element can be provided according to the invention on the guide of the machining unit or the workpiece table assigned to a linear degree of freedom. With vertical processing units, e.g. To compensate for the flexibility of your X-slide, control elements are mounted under the guide shoes of the guides. The non-constant stiffness of the X-slide can thus be compensated for depending on its respective Y-position.

In preferred further embodiments, the distance between two processing units, in particular between their work spindles, or between two workpiece tables of the machine tool can be changed via the at least one piezoelectric actuating element. In the simplest case it is Adjustment element between the two work spindles is provided, for example, in a parting line in order to adjust the spindle distance by widening the parting line.

Vibrations of the machine tool, which are generally in a frequency range of approx. 10-20 Hz, can also lead to position inaccuracies and displacements. It is therefore of particular advantage if at least one piezoelectric element which supports the machining unit or the workpiece table in a height-adjustable manner is provided to compensate for such vibrations (active vibration damping). For this purpose, the movement of the machine tool is detected with suitable vibration measuring elements, calculated and given to the actuating elements as displacement compensation values.

To determine the target / actual deviation on the tool or workpiece side, a mechanical, optical, capacitive or inductive measuring sensor, for example, can be provided that detects a displacement of the processing unit or the workpiece table directly or a parameter that determines the displacement as a sensing variable for controlling the at least one piezoelectric actuator detected. The first-mentioned parameters are particularly suitable for regulating the actuating element, while the second-mentioned parameters are parameters typical of machines, tools or devices, such as temperature or machining force, etc., the characteristics of which are determined in advance and then used for control in the can serve exact target positions. In an advantageous development, the at least one piezoelectric element itself can be provided as the measuring sensor. In the case of a dynamic position correction of the work spindle during the machining of a workpiece, the work spindle can not only be spatially adjusted by the adjusting element, but can also be kept continuously in this adjusted position. However, it is also possible to hold the work spindle in its position spatially adjusted by the adjusting element by means of a separate holding device. This holding device can be, for example, clamping elements that can be controlled as electrically as possible. In particular, piezoelectric elements can also be used as clamping elements.

Further advantages of the invention result from the description and the drawing. Likewise, the features mentioned above and those listed further can be used according to the invention individually or in combination in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention. The invention is shown schematically in the figures, so that the essential features of the invention can be clearly seen. The representations are not necessarily to be understood to scale.

It shows :

1 shows a first embodiment of a machine tool according to the invention with two vertical machining units in a perspective view; 2 shows an exemplary embodiment of a horizontal work spindle of a machine tool according to the invention, the work spindle being mounted displaceably in the Z direction;

3 shows another exemplary embodiment of a horizontal work spindle of a machine tool according to the invention, the work spindle being mounted so as to be displaceable radially to the Z direction; and

Fig. 4 shows a second embodiment of a machine tool according to the invention in a side view.

The machine tool 1 shown in FIG. 1 comprises a machine base in the form of a base support 2 and two processing units 3, the vertical work spindles 4 of which are displaceably guided in the X, Y and Z directions by means of a slide unit.

For this purpose, the carriage unit comprises an X-carriage 5, which is guided in horizontal guides 6 of the floor support 2 so as to be displaceable in the X-direction. Horizontal guides 7 are provided on the X slide 5 for a Y slide 8 carrying the two machining units 3. Each processing unit 3 has a quill-like Z-slide (not shown) with the work spindle 4, so that it can also be moved in the Z direction.

The two processing units 3, which are formed by a common housing block 9, are spaced in the X direction by a dividing joint 10 which is open to the front and in which a piezo-acting in the X direction electrical actuating elements 11 is located. The separation joint 10 can be widened by corresponding electrical control of the actuating elements 11 and the distance ΔX between the two work spindles 4 or between the tools 12 located therein can be changed.

The work spindle 20 shown in FIG. 2 is surrounded by three piezoelectric actuating elements 21 acting in the Z direction, which are arranged at equal angular intervals around the longitudinal axis 22 of the work spindle 20. The piezoelectric actuating elements 21 are attached at one end to the bearing 23 of the work spindle 20 and at the other end to the quinoline-like Z-slide (not shown). Since all three piezoelectric actuating elements 21 are electrically controlled for the same change in length .DELTA.z, the working spindle 20 or its tool 24 can be adjusted in length in the Z direction by the amount .DELTA.z. With different lengths of control of the three piezoelectric actuating elements 21, the work spindle 20 or the tool 24 can be tilted as desired from its original position designated 22.

Around the work spindle 30 shown in FIG. 3, three piezoelectric actuating elements 33 which act radially to the longitudinal direction 32 of the work spindle 30 are arranged on the outside and on the periphery of their bearing 31 at the outside and are supported at the other end on a housing (not shown). Each bearing 31 is held in a 3-point bearing 34 by its three piezoelectric actuating elements 32, each distributed around 120. Appropriate electrical length control of all piezoelectric actuating elements 33 of the two 3-point bearings 34 enables the work spindle 20 or its tool 35 either from the 32 shift the position in parallel by an amount Δr or tilt it. Due to the spherical adjustability, wobble errors of the work spindle 30 can be compensated for.

In the machine tool 40 shown in FIG. 4, piezoelectric adjusting elements 44, which act in the Y direction, are arranged between the base support 41 and the guides 42 for the slide unit described in FIG. 1 and a workpiece table 43. The workpieces to be machined with the tool 45 in the work spindle 46 are located on the workpiece table 43.

The transmission of vibrations of the base support 41 to the tool can be damped or eliminated by correspondingly rapid length control ΔY of the actuating elements 44. Depending on the position of the center of mass of the movable carriage unit, the forces acting on the guide 42 change, which can lead to geometrical deviations. With the adjusting elements 44 provided under the guides 42, e.g. Resilience of the carriage unit is compensated for and the non-constant rigidity of the carriage unit is compensated for depending on its respective position.

In a machine tool (1), in particular for machining workpieces, with a machining unit (3), at least one electrically controlled piezoelectric actuating element (11) is provided as the position correction device, in particular for a work spindle (4) of the machining unit (3). If a change in position is detected, the processing unit can be quickly mechanically moved into its respective target position.

Claims

claims

Machine tool (1; 40) for in particular machining workpieces, with a processing unit (3) and / or a workpiece table (43) and with a position correction device for the processing unit (3) or the workpiece table (3), characterized in that as Position correction device, in particular for a work spindle (4; 20; 30; 46) of the processing unit (3), at least one electrically controlled piezoelectric actuating element (11; 21; 33; 44) is provided.

Machine tool according to claim 1, characterized in that the effective direction of the at least one piezoelectric actuating element (11; 21; 44) approximately in the direction of a linear degree of freedom (X, Y, Z direction) of the processing unit (3) or the workpiece table (43) runs.

Machine tool according to Claim 2, characterized in that each linear degree of freedom (X, Y, Z direction) of the machining unit (3) or of the workpiece table (43) is assigned at least one piezoelectric actuating element (11; 21; 44) is.

Machine tool according to one of the preceding claims, characterized in that the effective direction of the at least one piezoelectric actuating element (33) is approximately radial to a linear degree of freedom (X-, Y-, Z direction) of the processing unit (3) or the workpiece table.

Machine tool according to Claim 4, characterized in that the machining unit or the workpiece table is mounted in a spatially adjustable manner via a multi-point holder (34) formed by at least two, preferably at least three piezoelectric actuating elements (33).

Machine tool according to Claim 5, characterized in that the machining unit or the workpiece table is mounted in spatially adjustable manner via at least two multi-point holders (34) arranged one behind the other in the direction of the linear degree of freedom (X, Y, Z direction).

Machine tool according to one of the preceding claims, characterized in that the at least one piezoelectric actuating element (44) on the guide (42) of the machining unit or the workpiece table (43) assigned to a linear degree of freedom (X, Y, Z direction) ) is provided.

Machine tool according to one of the preceding claims, characterized in that the distance between two machining units (3), in particular between their work spindles (4), or between two workpiece tables of the machine tool, can be changed via the at least one piezoelectric actuating element (11).

9. Machine tool according to one of the preceding claims, characterized by at least one machining unit or the workpiece table (43) height-adjustable mounting piezoelectric actuator (33; 44).

10. Machine tool according to one of the preceding claims, characterized by a sensor that a displacement of the processing unit (3) or the workpiece table (43) directly or a parameter determining the displacement as a sensing variable for controlling the at least one piezoelectric actuator (11th ; 21; 33; 44) recorded.

11. Machine tool according to claim 10, characterized in that the at least one piezoelectric actuating element (11; 21; 33; 44) itself is provided as the sensor.

12. Machine tool according to one of the preceding claims, characterized in that each piezoelectric actuator (11; 21; 33; 44) is assigned a holding device which the processing unit (3) or the workpiece table (43) in each case by the piezoelectric actuator (11; 21; 33; 44) holds predetermined position.