Control method for a machine tool and / or production machine

Abstract

The invention relates to a method for controlling a rotational movement of a tool (6) on the basis of a parts program in a machine tool (1), wherein the parts program specifies a retraction movement and a traversing movement to be performed by the tool (6), and the rotational movement (D) of the tool (6) is braked during the retraction movement and / or traversing movement.

Description

[0001] Description

[0002] Method for controlling a machine tool and / or production machine

[0003] The invention relates to a method for controlling a rotational movement of a tool in a tool and / or production machine.

[0004] DE 10 2010 015 221 A1 relates to a control device for a machine tool, which comprises a feed axis drive motor, a first power consumption calculation section which calculates the power consumption of the feed axis drive motor, a second power consumption calculation section which calculates the power consumption of a device which is designed to be operated with a constant power, and a motor control section which determines a target time constant which correlates with the acceleration time and / or the deceleration time of the feed axis drive motor, based on a sum of the power consumption which is calculated by the first power consumption calculation section and the power consumption which is calculated by the second power consumption calculation section, and controls the feed axis drive motor based on the target time constant.

[0005] DE 10 2019 103 563 A1 discloses a control device for a machine tool which controls the synchronous operation of a main axis and a feed axis.

[0006] In EP 2 952 991 A1 the movement pattern of a multi-axis system is to be energetically optimized. For this purpose a method is proposed in which a first axis and a second axis linked to it are moved with a respective first and second movement. Both movements begin together at a first point in time and end together at a second point in time. A time period is defined between the first and the second point in time. A respective acceleration profile of one or both movements is optimized such that it has at least one continuous transition from one acceleration value to another acceleration value within the time period.

[0007] Some machine tools are particularly well-suited for thread cutting; these are used in particular in tapping centers. Machine productivity is usually closely linked to spindle performance. Thermal problems, in particular, can reduce productivity.

[0008] The thermal problem is often solved by accelerating the spindle only at the rated current or by operating it at a current that is at or slightly above its rated current. However, this is disadvantageous, particularly with regard to dynamics, since only about a third of the possible acceleration is achieved.

[0009] The invention is based on the object of improving the control of the spindle , in particular with regard to thermal problems .

[0010] The object is achieved by claim 1, i.e. a method for controlling a rotational movement of a machine tool and / or production machine using a parts program in a machine tool, wherein a retraction movement to be carried out by the tool and a travel movement are specified in the parts program, wherein the rotational movement of the tool is braked during the retraction movement and / or travel movement, wherein the tool is accelerated in a first direction of rotation, wherein the tool rotating in the first direction of rotation is braked, wherein the tool is accelerated in a second direction of rotation, wherein the tool rotating in the second direction of rotation is braked, wherein a time duration of the braking of the tool rotating in the second direction of rotation is greater than a time duration of the braking of the tool rotating in the first direction of rotation.

[0011] The spindle is preferably braked during the period in which the spindle is moved to the next machining point.

[0012] The next processing point is, for example, the place where another thread is to be cut.

[0013] An embodiment is advantageous according to which, if the tool is braked only during the retraction movement, the tool is braked in such a way that the rotational movement is zero at a defined retraction plane.

[0014] In this way the spindle becomes less hot.

[0015] The defined retraction plane is advantageously between 5 mm and 15 mm, in particular between 8 mm and 12 mm.

[0016] Others are also possible, especially when an obstacle has to be overcome.

[0017] A further advantageous embodiment is that when the tool is braked during the travel movement, the tool is braked in such a way that the rotational movement is zero at the end of the travel movement.

[0018] The time available for braking is particularly long, so that only a slight heating up occurs during braking.

[0019] Another advantageous embodiment is one in which the rotational movement of the tool is decelerated during the retraction movement and at least partially during the travel movement. This embodiment also offers advantages with regard to thermal problems.

[0020] The tool is accelerated in a first direction of rotation, wherein the tool rotating in the first direction of rotation is decelerated, wherein the tool is accelerated in a second direction of rotation, wherein the tool rotating in the second direction of rotation is decelerated, wherein a time duration of the deceleration of the tool rotating in the second direction of rotation is greater than a time duration of the deceleration of the tool rotating in the first direction of rotation.

[0021] This is explained in more detail in the figure description.

[0022] Another advantageous embodiment is one in which the time required to carry out the specified travel movement of the tool specified in the part program is determined, with the required force required for braking being determined based on the time required.

[0023] The problem is also solved by a control device for carrying out the method.

[0024] The problem can also be solved by a machine tool having a control device.

[0025] The problem can also be solved by a computer program product comprising instructions which, when the program is executed by a control device, cause the control device to carry out the method.

[0026] The invention is particularly advantageous due to the utilization of flexible initial and final conditions of the tapping process.

[0027] The process usually begins and ends with a stop of all axes. However, it is particularly advantageous if the tapping process begins on the fly. In this case, the spindle and the feed axis involved are preferably synchronized at a user-defined coordinate (e.g., 1 mm before the thread) with the programmed speed and / or spindle speed.

[0028] A flying end is particularly described by the fact that when leaving the thread (e.g. 1 mm after the thread) a spindle speed (e.g. 6000 revolutions per minute) is specified by the user.

[0029] Another example of a sensible specification of the initial and / or end conditions would be that, as is the case today, the process begins and ends with all axes stopping, but the end is set to the retraction plane. The spindle then does not need to be decelerated to the position directly behind the drill hole (e.g., 1 mm), but only to the defined retraction plane (e.g., 10 mm).

[0030] From a thermal point of view, this is a big advantage.

[0031] The use of loss-minimal movement profiles is also an advantage.

[0032] Once the initial and / or final conditions described above have been defined, the motion profiles are advantageously calculated and output with minimal loss by a numerical control (NC). The user can seamlessly choose between time-optimized profile generation and loss reduction using minimal-loss profiles.

[0033] The method for parameterizing the loss-minimizing movement preferably comprises the following steps: The user preferably determines the maximum possible acceleration. Using a factor, the user can then transparently adjust the compromise between loss reduction and positioning time.

[0034] In the following, the invention is described and explained in more detail with reference to the exemplary embodiments shown in the figures.

[0035] It shows :

[0036] FIG 1 shows a typical speed cutting cycle by a machine tool,

[0037] FIG 2 an improved speed cutting cycle,

[0038] FIG 3 a possibility to reduce the thermal load,

[0039] FIG 4 shows the application of loss-minimal positioning to the tapping process from FIG 2 ,

[0040] FIG 5 Possibilities for minimal loss positioning with slightly increased maximum acceleration values,

[0041] FIG 6 a possibility for energy saving,

[0042] FIG 7 a machine tool,

[0043] FIG 8 a method and

[0044] FIG 9 a simulation program product .

[0045] FIG 1 shows a typical speed cutting cycle by a machine tool.

[0046] In the figure, the first step is a tapping (ZA) lasting 550 ms, followed by a travel to the next borehole (ZB) lasting 490 ms. Time t is given in seconds (s) in the figure. In this figure, ZB is characterized by movement and stopping.

[0047] The figure shows the speed curve of a machine during a tapping operation. During tapping, a spindle interpolates with the Z-axis. After tapping / tapping, the spindle stops, and the Y and Z axes move to the next hole. Then the tapping operation starts again.

[0048] During tapping, the spindle accelerates to, for example, 100 revolutions per second (or rev / s), i.e. 6000 revolutions per minute (see spindle speed SS and the curve 31), brakes, turns around, accelerates in the other direction, brakes, and stops. A short pause, caused, for example, by an exact stop, between the acceleration in a first direction and the acceleration in a second direction is possible; here, for example, 42 ms.

[0049] To perform this tapping operation quickly, the spindle is subjected to a current at maximum acceleration that the spindle is not designed to sustain. After tapping, there is a pause, followed by acceleration again.

[0050] This is very thermally stressful. If such a cycle lasts longer, e.g., 1 minute, the spindle becomes too hot. The machine tool stops working, sometimes for several minutes, due to the spindle's overheating. Alternatively, or in addition, a reduction in spindle acceleration may be necessary.

[0051] The figure also shows a curve 32 representing the speed YS in the Y-axis direction in mm / s, and a curve 33 representing the speed ZS in the Z-axis direction in mm / s. Figure 2 shows an improved speed cutting cycle.

[0052] The figure shows schematically the speed curve of the spindle in the form of a curve 35 . The spindle speed SS in the figure is at most 6000 rpm (revolutions per minute) or -6000 rpm in the other direction of rotation.

[0053] Current values ​​are also given in amperes A, which are supplied to the spindle at constant acceleration.

[0054] Unlike in FIG. 1, the spindle has a speed of -6000 rpm after tapping, and the time required for the spindle to reach the next drill hole is used for deceleration. During the 490 ms in ZB, the spindle can recover.

[0055] The effective current over the cycle is thus reduced to approximately 46 A (previously approximately 56 A), which corresponds to a saving of approximately 18%. The thermal load is reduced by the ratio of the squares of the effective currents (here by approximately 32%).

[0056] Tapping processes, in which the spindle is stationary before and after thread cutting, are problematic with regard to thermal stress.

[0057] If the braking of the spindle when moving out of the cut thread is avoided, as shown in FIG 2, the thermal load is reduced.

[0058] FIG 3 shows another possibility for reducing the thermal load.

[0059] Mathematical relationships are shown in FIG 3 .

[0060] FIG 3 shows a factor K=3 / 2 as well as an acceleration in the positive direction +A and an acceleration in the negative direction -A. A further drastic reduction in thermal stress can be achieved with loss-minimal acceleration profiles. The acceleration is then not constant, but decreases linearly over time to zero in phases.

[0061] A suitable profile is shown in FIG. 3. Here, the initial acceleration is selected to be approximately 50% greater than the conventional (constant) acceleration. This ensures that the distance covered in the same time is the same. The thermal load is thus reduced by approximately 25%.

[0062] For a loss-minimal positioning, a suitable acceleration curve a ( t ) and the resulting velocity profile v ( t ) are shown.

[0063] A classic acceleration profile is marked with 200 , an energy-minimizing profile or loss-minimizing profile is shown with 201 .

[0064] The integral under the velocity curves 203 and 204 is at least substantially equal, preferably exactly, i.e. the axle travels the required distance in the same time. However, the area under the square of the acceleration is reduced by approximately 25%. The current heat losses are at least substantially proportional to i 2 (especially if only the ohmic losses are considered, i.e. eddy current losses are neglected, and the fact that the resistance is temperature dependent is also neglected).

[0065] Approximately 25% less thermal losses occur. The maximum speed V at curve 203 kiass is greater than the maximum speed V Emin at curve 204 .

[0066] The formulas in FIG 3 also show the relationship between the classical thermal load FL kiass and the minimum loss thermal load FL Emknshown. Applied to the above tapping example in FIG 2, the profile shown in FIG 4 results.

[0067] FIG 4 shows the application of loss-minimal positioning to the tapping process from FIG 2. A curve 36 rotates in the figure at a maximum of 4500 rpm or -4500 rpm.

[0068] The effective current drops to approximately 37.2 A.

[0069] If less maximum current is available, the maximum acceleration value is advantageously adjusted accordingly. A factor of 1.5 is preferred for the minimum-loss profile (thus, a triangular profile), which achieves a savings of approximately 25%. This factor can therefore be selected between 1.0 (conventional profile) and 1.5 (energy-minimal, energy-minimal, or loss-minimal).

[0070] If the maximum acceleration during loss-minimal movement is only 3% higher than the base value, losses are already reduced by almost 15%. A 7.5% increase in acceleration already allows for a loss reduction of almost 20%.

[0071] It is advantageous if the tool is operated using a motion profile that minimizes losses.

[0072] As shown in the figure, the motion profile is preferably at least partially parabolic.

[0073] FIG 5 shows a potential for energy saving, comparing a conventional rectangular profile 504, a triangular profile 506 with approximately 25% energy saving and the mentioned 3% more acceleration a (see point 5A) and 7.5% more acceleration a (see point 5B) on the curve 505.

[0074] The figure also shows a conventional profile 501, an energy-minimal profile 502 (approximately 3% more acceleration), and an energy-minimal profile 503 (7.5% more acceleration). The method is advantageously scalable to any value of the conventional acceleration.

[0075] Loss-minimal profiles can also be determined while observing the jerk limitation.

[0076] In principle, the time before the tapping process can also be used for a smooth spindle acceleration. The procedure is similar to shutting down or braking the spindle at the end of the process, as already explained.

[0077] The potential for energy savings is also present here, and preferably depends on the time available. For illustration, the speed curve for the classic profile for this process is shown in FIG. 6.

[0078] Curve 37 illustrates a run-up 100 and a run-down 110 of the spindle.

[0079] Also advantageous, as shown in FIG 6, is a method for controlling a rotational movement of a tool using a parts program in a machine tool, wherein a feed movement to be carried out by the tool and a travel movement are specified in the parts program, wherein the tool is accelerated during the feed movement and / or travel movement.

[0080] The acceleration preferably takes place at least partly on a journey to the processing point.

[0081] In this way, rotation can be achieved without damaging the spindle.

[0082] FIG 7 shows a tool and / or production machine 1 and a controller 2 .

[0083] They form a system 3. In the figure, the machine tool and / or production machine 1 comprises a spindle 5, to which a tool 6 (particularly suitable for thread cutting) is attached. The machine 1 is designed to carry out the method described in the drawing.

[0084] A spindle rotation (and thus a rotation of the tool) is marked with D in the figure.

[0085] A tool tip or an engagement point of the tool 6 is advantageously described by a tool center point 61 (TCP for short). The tool center point 61 is located at a tool tip in the figure.

[0086] In the figure, a workpiece 8 is located on a work table 7. The tool 6 advantageously serves to machine the workpiece 8.

[0087] The figure shows an optional means for detecting an actual position value 10 of the TCP 61, for example in the form of a rotary encoder or linear scale. The arrangement of the means for detecting the actual position value 10 is shown in this figure purely as an example.

[0088] An actual speed and / or an actual acceleration of the TCP 61 is optionally detected in the figure by a sensor 11. The sensor 11 is arranged in the figure at or near the tool center point 61. The sensor 11 can also be arranged near the detection means 10. The sensor 11 can also be arranged on or near the workpiece 8, which is being machined by the tool and / or production machine 1.

[0089] The controller 2, in particular embodied as a numerical controller, has a computer program product 21 in the figure. The computer program product 21 comprises instructions which, when the program is executed by the controller 2, cause the controller 2 to carry out the described method. For this purpose, the computer program product 21 is advantageously stored in the controller.

[0090] FIG 8 shows a method .

[0091] In a process step S 1, a retraction movement and a travel movement to be carried out by the tool are specified.

[0092] Preferably, a target speed of the tool is also specified.

[0093] In a process step S2, the tool is accelerated in a first direction of rotation.

[0094] In a method step S3, the tool rotating in the first direction of rotation is decelerated. The rotational movement of the tool is decelerated during the retraction movement and / or travel movement.

[0095] In a process step S4, the tool is accelerated in a second direction of rotation.

[0096] In a method step S5, the tool rotating in the second direction of rotation is decelerated. The rotational movement of the tool is decelerated during the retraction movement and / or travel movement.

[0097] A time duration of braking of the tool rotating in the second direction of rotation is greater than a time duration of braking of the tool rotating in the first direction of rotation.

[0098] Also advantageous is a simulation program product 1000, see FIG. 9, designed as a digital twin of the tool and / or production machine 1, comprising instructions which, when the program is executed by a computer 1100 or a simulation unit, cause the latter to map the method.

[0099] In this way, tapping can be simulated and, if necessary, thermal stress can be estimated.

[0100] The process can be easily mapped digitally.

[0101] The simulation program product can be executed externally on a separate computer or on the control unit 2.

Claims

Patent claims 1. Method for controlling a rotational movement (D) of a tool (6) using a part program in a machine tool and / or production machine (1), wherein a retraction movement and a travel movement to be carried out by the tool (6) are specified in the part program, wherein the rotational movement (D) of the tool (6) is braked during the retraction movement and / or travel movement, wherein the tool (6) is accelerated in a first direction of rotation, wherein the tool rotating in the first direction of rotation (6) is braked, wherein the tool (6) is accelerated in a second direction of rotation, wherein the tool (6) rotating in the second direction of rotation is braked, wherein a time duration of the braking of the tool rotating in the second direction of rotation is greater than a time duration of the braking of the tool rotating in the first direction of rotation.

2. Method according to claim 1, wherein, if the tool (6) is braked only during the retraction movement, the tool (6) is braked such that the rotational movement is zero at a defined retraction plane.

3. Method according to claim 2, wherein the defined retraction plane is between 5 mm and 15 mm, in particular between 8 mm and 12 mm.

4. Method according to one of the preceding claims, wherein, when the tool (6) is braked during the travel movement, the tool (6) is braked in such a way that the rotational movement is zero at one end of the travel movement.

5. Method according to one of the preceding claims, wherein the rotational movement (D) of the tool (6) is braked during the retraction movement and at least partially during the travel movement.

6. Method according to one of the preceding claims, wherein the time required to carry out the specified travel movement of the tool (6) is determined on the basis of the travel movement of the tool (6) specified in the part program, wherein the time required to exert force for braking is determined on the basis of the time period.

7. Method according to one of the preceding claims, wherein the spindle is braked during the period in which the spindle is moved to a next machining point.

8. Method according to one of the preceding claims, wherein a target speed is specified.

9. Method according to one of the preceding claims, wherein the tool (6) is operated based on a loss-minimal movement profile.

10. The method according to claim 9, such that the movement profile is at least partially parabolic.

11. Method according to one of the preceding claims, wherein a feed movement to be carried out by the tool (6) and a further travel movement are specified in the part program, wherein the tool (6) is accelerated during the feed movement and / or the further travel movement.

12. Control device for carrying out the method according to one of claims 1 to 11.

13. Machine tool and / or production machine (1) comprising a control device according to claim 12.

14. Computer program product (21) comprising instructions which, when the program is executed by a control device (2), cause the control device (2) to carry out the method according to one of claims 1 to 11.

15. Simulation program product (1000), designed as a digital twin of the machine tool and / or production machine (1) according to claim 13, comprising instructions which, when the program is executed by a computer (1100) or a simulation unit, cause the computer or simulation unit to map the method according to one of claims 1 to 11.

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