WO2016120121A1

WO2016120121A1 - Method for compensating for deformations of a rotary pivoting unit of a machine tool on account of dynamic movement operations

Info

Publication number: WO2016120121A1
Application number: PCT/EP2016/050974
Authority: WO
Inventors: Jürgen Röders
Original assignee: P + L Gmbh & Co. Kg
Priority date: 2015-01-28
Filing date: 2016-01-19
Publication date: 2016-08-04
Also published as: DE102015201439A1

Abstract

The invention relates to a method for compensating for deformations of a rotary pivoting unit (1), provided with a workpiece, of a machine tool on account of dynamic movement operations, in which, during the machining of the workpiece (2), the weight of the workpiece (2) on the rotary pivoting unit (1), linear accelerations and/or decelerations of the rotary pivoting unit (1), the torque of the drive of the pivot axis (10) and the position of the pivot axis (10) of the rotary pivoting unit (1) are determined and at least one compensation value is calculated from these data and fed to the machine controller in order to correct a running machining program.

Description

Method for compensating deformations of a rotary pivot unit of a machine tool due to dynamic movement processes

description

The invention relates to a method for compensating deformations of a workpiece provided with a rotary pivoting unit of a machine tool due to dynamic movement processes.

The dynamic motion processes contemplated by the invention include accelerations and decelerations that result during machining of a workpiece. The compensation method according to the invention also relates to the workpiece weight or to dynamic deformations which arise as a function of the workpiece weight.

The dynamics of machine tools and thus the available acceleration in the axes are constantly being increased. However, high accelerations lead to undesirable deformations in the machine tools and thus to undesirable machining inaccuracies. For machine axes of machine tools that move the workpiece to be machined, these are additionally influenced by the mass of the workpiece. The larger the mass of the workpiece, the greater the resulting deformations and deviations in the machining.

This is especially true for machine tools in which the workpiece is clamped on a rotary pivot unit and moved by means of two rotary axes. In addition, when the rotary pivot unit is moved along a linear axis, further effects from the acceleration of this linear axis are added. For mechanical systems, an initial approximation of an additive superimposition of the individual deformations can be assumed. This is also the approach in the compensation method according to the invention.

For a rigidly designed rotary swivel unit, deformations caused by the workpiece will only have a significant effect when it reaches a certain mass. Smaller workpieces with low weights only lead to negligible deformations. The swing bridge of the rotary swivel unit is deformed only by its own weight, for which the machine tool can be mechanically adjusted during commissioning. Larger workpieces can be stretched only relatively centric with a pivoting in units typically way cranked arrangement of the machine axes. As a result, the center of gravity of the workpiece is also relatively centric. The determining factor for the deformation of rigid rotary swivel units is thus the mass of the workpiece. This leads to a deflection of the rotary pivot unit down. The compression is composed of the compliance of the bearings, the guide carriage, when the rotary pivot unit is still on another linear axis, and a deformation of the mechanical components, such as the castings that make up the rotary pivot unit. With the aid of various reference weights, the static weight-dependent deformation can be easily measured, as also known from EP 2 735 928 A1. However, the deformation must not be uniform, but may be smaller due to the design of the rotary pivot unit on the one hand, for example, the side with the drive and the larger bearing than on the opposite side. It can therefore also come to a slight tilting of the axis by the workpiece weight. As an alternative to measuring the properties of the pivoting unit, these can also be calculated using modern methods, for example finite elements.

In addition, the stiffness of the pivot unit is not the same in all directions. As a result, due to the workpiece and its own weight of the pivot bridge deformation of the rotary pivot unit will also depend on the position of the pivot axis. If the pivot axis is at 90 °, it will be different than when it is at 0 ° or corresponding intermediate positions. This also applies to the strength of the tilt of the pivot axis by different compression of the pivot unit on both sides. Thus, in addition to the workpiece weight and the position of the pivot axis must be included for the compensation of static workpiece and self-weight induced deformations.

In practice, in addition to the described linear compression and the tilting of the pivot unit at different positions of the pivot axis also comes to a Deformation due to torsion by the eccentric load of the pivot axis, eg because of the cranking of this. However, the torsion should not be considered at this point, but only as a second effect, since in the torsion and dynamic portions of the axis movement play a role, as described below. To separate the deformation by torsion from the deformation by linear compression, as known in mechanics, a reference point or a reference line can be selected, for example, the pivot axis itself. The deformation is composed, based on the pivot axis, of a linear and a rotary portion together.

The workpiece weight and the position of the pivot axis are therefore only used to calculate the deflection of the pivot unit with the workpiece down and the tilting of the pivot axis by different compression at the ends of the pivot unit. As a basis for the calculation, previously performed measurements or even modern calculation methods, such as finite elements serve. This consideration is purely static and a twisting of the swing bridge by the eccentric load of the rotary actuator is not provided so far, as it also applies the dynamic effects to consider.

The invention has for its object to provide a compensation method of the type mentioned, which with a simple structure and simple, cost-effective applicability high-quality operation of a machine tool, in particular a 5-axis milling machine allows.

According to the invention the object is achieved by the combination of features of claim 1, the dependent claims show further advantageous embodiments of the invention.

According to the invention, there is thus provided a method of compensating for deformations of a rotary swivel unit of a machine tool due to dynamic motions in which, during machining of the workpiece, the weight of the workpiece on the rotary swivel unit, linear accelerations and / or decelerations of the swivel unit, the torque of the Drive the rotary pivot unit and determines the position of the pivot axis of the rotary pivot unit and calculated from these data at least one compensation value and the machine control is supplied to correct a current machining program.

It is thus provided according to the invention that first the workpiece weight is determined on the rotary pivot unit. The workpiece weight can, for example, by Moving the linear axis, on which the rotary pivot unit is located, can be easily determined with a short acceleration by measuring the forces required for the acceleration over the current required in the drive. If a previously identical measurement was performed without a workpiece, the difference between the currents or the forces on the workpiece weight can be deduced. The determined workpiece weight is then, in addition to the position of the pivot axis, the input quantity for the compensation with which the mechanical deviations in the control caused by different workpiece weights can be offset. These are the input quantities for the first effect.

If, during machining, larger chippings occur which significantly change the weight of the workpiece, this can be redetermined at any time in the meantime using the method described above. The currently valid workpiece weight serves as the input value for the compensation.

A disadvantage of the method according to EP 2 735 828 A1 is that acceleration-related forces and deformations are not included. According to the invention, therefore, the torque of the drive of the pivot axis is included for the compensation. The torque of the swivel unit is basically divided into four sub-moments.

During the process of the pivot axis, this must overcome the frictional forces in bearings, seals, etc. This moment is essentially speed-proportional and can be easily determined by reversing the axis.

Furthermore, part of the torque is needed to hold the pivot unit in certain positions, e.g. when the rotary swivel unit is at 90 °. Due to the cranking, a specific torque is required, in particular for small workpieces, in order to hold the eccentric axis with respect to its center of gravity by the pivot drive.

The third partial torque relates to the acceleration of the pivot axis. Especially with 5-axis simultaneous machining of complex workpieces, the swivel axis must constantly accelerate and decelerate, which leads to high torques in the drive during dynamic machining operations. The fourth partial torque results from machining forces during machining, which, depending on the machining location, act on the drive of the pivot axis via a lever. _c

5

In practice, the frictional forces are usually of secondary importance. In high-precision machining, the machining forces are also relatively small. The decisive part of the torque in the pivot axis then make up the other two partial moments, which are formed from the eccentricity of the entire pivot unit, consisting of workpiece and the pivot bridge, and the acceleration and deceleration processes. Both overlap and lead to deformations, essentially a twisting (torsion) of the swivel bridge, in particular if the drive is provided only on one side. Therefore, it is desirable to compensate this effect also in the control. This is also important because the position sensor for the pivoting unit is usually arranged as close to the drive as possible for reasons of control engineering. However, this has the consequence that there is no direct information about the twisting of the swivel bridge. If the mechanical properties of the pivoting bridge, for example by metrological determination or calculation (finite elements or the like) are known, but with the help of the torque in the pivot axis, the deformation of the swing bridge can be determined. The torque is in turn easily determined by the motor current required in the drive of the pivot axis. The thus determined from the torque of the rotary actuator, possibly with deduction of friction components of the torque, deformation of the swing bridge is another input for the compensation to compensate for the distortion of the pivot unit resulting dimensional variations in the control. This second effect is taken into account in addition to the static compensation for the total compensation described above.

In addition, as described above, when the rotary pivot unit executes a linear motion, linear axis acceleration and deceleration operations may result in deformations of the entire rotary pivot unit and hence dimensional variations in machining. For example, when the rotary swivel unit is mounted on a traveling machine table, it can deflect during highly dynamic machining, much like a car that descends on the rear axle when accelerating and comes up on the front axle. In contrast to the car, however, the pivoting unit is not so rigid in itself that the deformations of this kind would be negligible. So it's not just about a compression of the rotary pivot unit on the carriage of the linear axis, but also due to the linear acceleration induced deformations of the rotary pivot unit itself. The position of the pivot axis also plays a role. The amount of deflection of the rotary pivot unit is different for different Schwenkachspositionen. This effect also leads to undesirable deviations in dynamic processing and can be compensated. If the workpiece weight, as described above, is known about the Motor current of the actuator can be closed to the currently running acceleration. In addition, the acceleration is of course known as the setpoint by the predetermined for the execution of the processing control path for the individual axes. The acceleration of the linear axis can thus be easily determined from the actual values of the motor current or from the setpoint values of the acceleration. If the acceleration-related amount of deflection of the machine table by metrological determination, for example by appropriate test machining with different workpiece weights and different pivot angles of the pivot axis, or computational determination from the known mechanics of the machine for different accelerations is known, can in this way during processing for different Acceleration values of the linear axis for the rotary pivot unit, the dimensional deviation can be compensated by compression. This is a third effect for the compensation of deformations caused by different workpiece weights and accelerations in a machine tool with a rotary pivoting unit.

The three described effects and the associated compensations can be applied individually or as an additive. Due to non-linear behavior, it may also be useful to enter all described input variables, ie workpiece weight, position of the pivot axis, motor current / torque of the pivot axis and acceleration of the linear axis in a complex model stored in the control for the machine as common input variables and calculate compensation values. The underlying model can be determined metrologically or by calculation (for example with finite elements) from the known mechanics or as a combination of both.

In certain machine tool designs, the effect may be subordinated to the linear accelerations, e.g. because the acceleration capacity of the linear axis is relatively limited. Then this effect can also be neglected and only the deformations of workpiece weight, position of the pivot axis and motor current / torque of the pivot axis are taken into account.

After the deviations resulting from the described effects have been calculated in the machine control, the required compensation values can easily be calculated for the linear and rotary axes of the machine. Since these are 5-axis machines, both the 5-axis position and angle errors can be corrected so that the deviations due to the weight and dynamic deformation of the rotary unit are fully compensated, both in direction and position. The correction takes place during processing by appropriate adjustment of the setpoints for the axes. The compensation model for calculating the required corrections is permanently stored in the controller.

In the following the invention will be described by means of an embodiment in conjunction with the drawing. Showing:

1 is a perspective view of a 5-axis milling machine according to the invention,

2 is a simplified representation of the deflection of the machine table due to the workpiece weight,

3 is an end view of the rotary pivot unit analogous to FIG. 2,

4 is an end view of the rotary pivot unit, analogous to the illustrations of FIGS. 2 and 3,

Fig. 5 is an end view of the rotary pivot unit, analogous to FIG. 3, and

Fig. 6 is a view of the rotary pivot unit for acceleration to the right.

1 shows a perspective view of a 5-axis milling machine with a rotary pivot unit 1. In detail, the machine tool has a frame 3 with a portal 4 on which a slide 5 is mounted horizontally displaceable (Y-axis), on which vertically movable, a carriage 6 is mounted, which supports a rotating spindle 7, on which a tool 8 is mounted. A machine table 9 is mounted on the rotary swivel unit 1 and is rotatable about a pivot axis 10 (see FIGS. 2 to 5). As shown in FIGS. 4 and 5, the machine table 9 is pivotable about an axis of rotation 10 perpendicular to the pivot axis 1 1. The rotary pivot unit 1 can be moved in the X direction (not shown in FIG.) Parallel to the pivot axis 10. The design of the 5-axis milling machine shown in FIG. 1 is known from the prior art, so that further explanations can be dispensed with ,

FIGS. 2 to 6 each show simplified views, from which the positions without deformations result in dashed lines. The solid lines each show the loaded state, which results from the tool weight and the effect of accelerations and torques and the position of the rotary pivot unit. It is understood that the illustrations of Figs. 2 to 6 for clarity of the invention a O

exaggerated, not necessarily true to reality deformation, tilting or torsion.

2 shows a side view of the rotary pivot unit 1 with a deflection of the machine table 9 due to the weight of a workpiece 2. From the comparison of the dashed lines (unloaded state) with the solid line, it can be seen that the machine table 9 springs in more strongly on the right side than on the left side. The pivot position of the rotary pivot unit 1 is 0 °. The tilting results from the workpiece weight. It can be seen that the pivot bridge 12 springs in several places, once on the carriage at the bottom of the table, but also on the counter bearing. Here, the compression is shown as a relative displacement between the counter bearing and counter bearing plate.

3 shows an end view of the rotary pivot unit. 1 As in Fig. 1, the deflection of the machine table 9 is shown due to the weight of workpiece 2. For reasons of simplification, the tilting of the pivoting bridge by different compression at both ends is not shown. The pivot position of the pivot axis 10 is 0 °.

From Fig. 4 shows a representation of the rotary pivot unit 1 in a frontal view, wherein the pivot axis is set to 90 °. It can be seen with respect to the center of the pivot axis 10 that this moves down and that there is a twist due to torsion. The tilting of the rotary pivot unit is not shown for reasons of clarity.

FIG. 5 shows the subject matter according to the invention when the swivel unit carries out a rotational acceleration in the direction of the arrow. The rotary pivot unit 1 is shown in frontal view. The unloaded state is indicated by dashed lines. The solid lines show how the rotary swivel unit 1 deforms under the load of the workpiece weight, so springs down and twisted (twisted). Angle α indicates the amount of torsion by workpiece weight. With dotted lines is shown how the rotary pivot unit 1 under load of the workpiece weight and under an applied in the direction of the arrow rotational acceleration of the pivot axis 10 further rotated. The dotted workpiece shown is even more tilted than that shown by a solid line, since the spin leads to additional torsion of the swing bridge. Angle β indicates the amount of torsion by spin. The total torsion is composed of the sum of angle α and angle β. A possible tilting of the rotary pivot unit 1 is not shown for reasons of clarity. FIG. 6 shows the behavior of the rotary pivot unit 1 when it performs an acceleration to the right in the direction of the arrow. Dashed lines show the turnstile unit when it is already loaded with the workpiece weight but does not execute a linear acceleration. Solid lines show how the rotary swivel unit deforms when accelerated in the direction of the arrow. This springs on the left side down and on the right side upwards. The rotary pivot unit tilts in the case opposite to the tilt caused only by the workpiece weight. The swivel position is 0 °. It thus follows that the deflection due to the acceleration is weaker than in the state shown in Fig. 2, that is partially compensated.

It thus follows that according to the invention in particular the torque of the pivot axis 10, the position of the pivot axis 10, the linear acceleration of the pivot unit and the workpiece weight are used as input variables for the correction. These input quantities or partial compensation values are inventively determined separately and then combined to calculate the total compensation.

LIST OF REFERENCE NUMBERS

1 rotary swivel unit

2 workpiece

3 frame

4 portal

5 sleds

6 sleds

7 spindle

8 tool

9 machine table

10 pivot axis

1 1 rotation axis

12 swing bridge

Claims

claims

1 . Method for compensating for deformations of a workpiece-equipped rotary pivoting unit (1) of a machine tool due to dynamic movement processes, during which the weight of the workpiece (2) on the rotary pivoting unit (1), linear accelerations and / or during machining of the workpiece (2) Delays of the rotary pivot unit (1), the torque of the drive of a pivot axis (10) of the rotary pivot unit (1) and the position of the pivot axis (10) of the rotary pivot unit (1) determined and calculated from these data at least one compensation value and the machine control to correct a current Processing program is supplied.

2. The method according to claim 1, characterized in that all compensation variables are used for calculating the compensation value.

3. The method according to claim 1, characterized in that only individual compensation quantities are used for calculating the compensation value.

4. The method according to any one of claims 1 to 3, characterized in that for calculating the torque of the drive of the pivot axis (10) frictional forces in seals and / or bearings of the pivot axis (10) are taken into account.

5. The method according to any one of claims 1 to 4, characterized in that the accelerations are determined by measuring the respective motor currents used for movement.

6. The method according to any one of claims 1 to 5, characterized in that the workpiece weight is re-measured during processing in a predetermined time interval.

7. The method according to any one of claims 1 to 6, characterized in that the correction of the current machining program during machining of the workpiece (2) for adapting the respective set values for the individual axes of movement of the machine tool takes place.

8. The method according to any one of claims 1 to 7, characterized in that in the machine control a compensation model, with which the determined compensation values are processed, is deposited.