METHOD FOR OPERATING A MACHINE TOOL AND / OR PRODUCTION MACHINE

Description

[0001] The invention relates to a method for operating a machine tool and / or production machine.

[0002] Machine tools and / or production machines are designed for machining workpieces. Components for various applications can be created using them.

[0003] Precise and fine machining is necessary, for example, in tool and mold making. Accurate shapes are important, for instance, in the production of molds for PET bottles or Lego bricks.

[0004] Furthermore, high manufacturing accuracy is required for optical components such as spectacle lenses, lens or eyepiece components and components for telescope mirrors, cameras and microscopes.

[0005] Similarly, high manufacturing accuracy is also necessary in other machining technologies, such as when turning pump pistons, synchronous gears, injection nozzles or bearing bushings.

[0006] Fine machining aims for very high machining accuracy and a very high surface quality on the component or workpiece.

[0007] Examples of this fine machining include finishing operations in milling for tool and mold making, fine or fine finishing, or fine or precision turning of turned parts.

[0008] Finishing often follows roughing to achieve the required surface finish as well as dimensional and geometric accuracy. In the context of workpiece accuracy requirements, the terms finishing, fine finishing, and fine finishing are well-known in the industry.

[0009] Finishing is typically used for final or finishing work, but a subsequent manufacturing step, such as polishing, may also be necessary. Improvements are achieved, for example, by reducing process forces and using very precise machines and tools. However, this is very costly.

[0010] If unwanted vibrations occur at a machining point between the tool and the workpiece during finishing, this negatively affects quality and surface finish. This necessitates time-consuming and expensive manual rework, such as polishing. This leads to increased costs and lead times.

[0011] US Patent 2019 / 126474 A1 describes a method and device for a computer-controlled motion machine that iteratively calculates a numerical "jerk," the motion derivative of acceleration, using real-time feedback from a motion-controlled system to achieve both a desired position and velocity at the next waypoint. The output of the motion machine is only the desired acceleration, which is then passed to a motor driver without requiring any intermediate calculations of position or velocity. A second, internal feedback loop maintains the desired acceleration or torque at the motor shaft based on the acceleration output of the motion machine, which may utilize nonlinear correction tables. Waypoints that include both position and velocity are inputs to the motion machine.The time to the next waypoint is calculated and not provided as input. Optimization of movements to the next waypoint is based on the smoothest velocity change during the movement. Implementation examples include mechanical, bi-axis SCARA arm motion systems.

[0012] EP 3470943 A2 describes a method for calculating guide variables for interpolating single axes of a precision machine based on a given 3D toolpath, in which, first, the velocity, acceleration, and jerk profiles of all interpolating axes are calculated continuously and without specifying limit values ​​for all points of the toolpath, assuming a freely chosen path speed or single-axis speed, and then, velocity, acceleration, or jerk profiles are changed on areas of the 3D toolpath.

[0013] The invention is based on the objective of achieving a high surface quality with high productivity.

[0014] The problem is solved by claim 1, i.e., a method for operating a machine tool and / or production machine comprising the following steps: Comparing at least one target position value of a machine axis and / or a tool center point with an actual position value and / or comparing at least one target speed of the machine axis and / or the tool center point with an actual speed and / or comparing at least one target acceleration of the machine axis and / or the tool center point with an actual acceleration, generating at least one quality value based on the comparison or...The comparisons, whereby a difference signal is determined from the target and actual position values ​​and / or from the target and actual speeds and / or from the target and actual accelerations over a specific period, and the difference signal is fed into a signal analysis procedure, whereby quantities determined by the signal analysis are incorporated into the actual quality value (Gist), comparison of a target quality value with the actual quality value, reduction of a feed rate and / or acceleration and / or jerk of the machine axis and / or the tool center point if a defined deviation of the actual quality value from the target quality value is exceeded, or storage of information that the defined deviation of the actual quality value from the target quality value has been exceeded.

[0015] This ensures fine processing in real time or allows for high accuracy through area-specific or point-accurate post-processing, as the necessary information is available.

[0016] The procedure is advantageous with the following additional step: - Increasing the feed rate and / or acceleration and / or jerk of the tool center point if the defined deviation or another defined deviation of the actual quality value from the target quality value is undershot.

[0017] In other words, this is advantageous: If the defined deviation is exceeded, the described reduction occurs. This improves accuracy. This is accompanied by an improvement or alignment of the actual quality value towards the target quality value. If the defined deviation or a further defined deviation falls below the threshold, the described increase occurs.

[0018] Preferably, the further defined deviation is decisive for increasing it in order to avoid constantly alternating reduction and increase of the feed rate and / or acceleration and / or jerks.

[0019] An advantageous embodiment is one in which the target quality value and / or the defined deviation and / or the further defined deviation are stored in a part program and / or entered into a control system of the machine tool and / or production machine, in particular a numerical control system.

[0020] The values ​​can therefore be entered beforehand as well as directly during operation, especially by a user at the machine.

[0021] A setting stored in the control system is usually not changeable by the user, whereas a setting stored in the parts program allows for changes during operation.

[0022] An advantageous embodiment is one in which the actual position and / or the actual velocity and / or the actual acceleration are recorded by means of at least one measuring system.

[0023] The possible measurement systems are explained further below.

[0024] An advantageous embodiment is one in which the measurement frequency of the actual position and / or the actual velocity and / or the actual acceleration is at least 500 / s and at most 1500 / s, preferably at least 800 / s and at most 1200 / s, in particular 1000 / s.

[0025] This ensures a sufficiently good and accurate measurement.

[0026] An advantageous embodiment is one in which the actual position value is detected by a rotary encoder and / or a linear scale arranged in or on the tool and / or production machine.

[0027] Preferably, the actual position is recorded using a glass scale or other length measuring device. Other optical measuring systems are also conceivable.

[0028] The linear scale, especially a glass scale, is usually positioned at a certain distance from the point of action, i.e., the Tool Center Point (TCP).

[0029] An advantageous embodiment is one in which the actual speed and / or the actual acceleration is detected by at least one sensor, wherein the sensor is arranged at or near the tool center point or at or near a workpiece which is machined by the machine tool and / or production machine.

[0030] Preferably, the sensor for measuring the actual acceleration is an accelerometer. This advantageously measures the acceleration in at least one or three spatial directions.

[0031] The sensor for measuring the actual acceleration is advantageously located near the TCP, for example near a milling head.

[0032] The sensor for measuring the actual speed is advantageously located near the TCP.

[0033] Alternatively, the actual speed at the TCP can be calculated from the current position and acceleration.

[0034] It is advantageous to take measurements at, or at least in close proximity to, the point where a vibration occurs. A vibration that the described method aims to avoid or reduce can occur on the TCP side as well as on the workpiece side.

[0035] The task can also be solved by a control system for a machine tool and / or production machine.

[0036] The problem can also be solved by a computer program product comprising commands which, when the program is executed by the controller, cause it to carry out the procedure.

[0037] The invention offers the advantage that, for the finishing process, it is not necessary to permanently reduce the jerk and, if applicable, the acceleration of the machine tool axes involved in the finishing process in order to achieve a reduced excitation of mechanical vibrations in the machine tool and / or production machine. Dynamic operation is possible. This shortens the machining time of a workpiece on the machine tool and / or production machine. As a result, costs are reduced and cycle times are shortened.

[0038] The invention will now be described and explained in more detail with reference to the embodiments shown in the figures.

[0039] They show: FIG 1 a system comprising a machine tool and / or production machine and a control system, FIG 2 a machining operation of a workpiece, FIG 3 process steps, FIG 4 an exemplary embodiment of the process, FIG 5 another possible machine tool and / or production machine, FIG 6 another possible machine tool and / or production machine.

[0040] FIG 1 Figure 1 shows a machine tool and / or production machine 1 and a control system 2. They form a system 3. The machine tool and / or production machine 1 includes a spindle 5 in the figure, to which a tool 6 (in the figure for milling) is attached.

[0041] A spindle rotation (and thus a rotation of the milling tool) is marked with D in the figure.

[0042] A tool tip or point of engagement of the tool 6 is advantageously described by a Tool Center Point 61 (abbreviated: TCP). The Tool Center Point 61 is located at a tool tip in the figure.

[0043] In the figure, a workpiece 8 is located on a worktable 7. The tool 6 is advantageously used to machine the workpiece 8.

[0044] The figure shows a means for recording a position value 10 of the TCP 61, for example in the form of a rotary encoder or linear scale.

[0045] The arrangement of the means for recording the actual position value 10 is shown in this figure purely as an example. Reference is made to the explanations regarding FIG 5 referred to.

[0046] The actual velocity and / or acceleration of TCP 61 is detected by a sensor 11 in the figure. The sensor 11 is located at or near the Tool Center Point 61 in the figure. The sensor 11 can also be located near the detection means 10.

[0047] The sensor 11 can also be located on or near the workpiece 8, which is processed by the machine tool and / or production machine 1.

[0048] The controller 2, in particular configured as a numerical controller, includes a computer program product 21 as shown 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 execute the program in FIG 4 to carry out the described procedures.

[0049] The computer program product 21 is advantageously stored in the control system for this purpose.

[0050] FIG 2 shows the machining of workpiece 8, in particular a milling operation.

[0051] Tool 6 removes material in the figure. TCP 61 is located at the tip of the tool.

[0052] The invention is well suited for processes involving material removal. Other applications are also possible.

[0053] FIG 3 shows process steps of the procedure for operating a machine tool and / or production machine.

[0054] In a process step S1, at least one target position value of the Tool Center Point 61 is compared with an actual position value of the Tool Center Point 61.

[0055] The target position is advantageously predefined and stored or available in control unit 2. The target position can also be calculated by the control unit. The actual position is advantageously measured, in particular using the means for acquiring an actual position value 10.

[0056] In process step S2, at least one target speed of Tool Center Point 61 is compared with an actual speed of Tool Center Point 61.

[0057] Advantageously, the target speed is predefined and stored in the controller 2. The actual speed is advantageously measured using sensor 11.

[0058] In process step S3, at least one target acceleration of Tool Center Point 61 is compared with an actual acceleration of Tool Center Point 61.

[0059] Advantageously, the target acceleration is predefined and stored in control unit 2. The actual acceleration is advantageously measured using sensor 11.

[0060] It is possible to perform the process steps S1, S2, and S3 sequentially. A different order of the process steps is also possible.

[0061] Furthermore, it is also possible to carry out only one or two of the aforementioned procedural steps.

[0062] In process step S4, a quality value is formed based on the comparison(s).

[0063] The actual quality value is advantageously a number. The target quality value is also advantageously a number.

[0064] In process step S5, a comparison is made between a target quality value and the actual quality value.

[0065] It is advantageous if the target quality value has already been defined beforehand. It is advantageous if the target quality value is stored in the control system.

[0066] The target quality value is advantageously dependent on the intended accuracy.

[0067] In A1, a query is performed to determine whether a defined deviation of the actual quality value from the target quality value has been exceeded.

[0068] It is advantageous if the defined deviation has already been defined beforehand. It is advantageous if the defined deviation is stored in the control system.

[0069] The defined deviation, and also another defined deviation, are advantageously a number.

[0070] If the defined deviation was not exceeded - marked with n - no measures are taken in procedure step S6.

[0071] If the defined deviation is exceeded - marked with j - in a process step S7 either a reduction of the feed rate and / or acceleration and / or jerk of the Tool Center Point 61 (preferably in real time) or a saving or storage of information about the fact that the defined deviation of the actual quality value from the target quality value has been exceeded.

[0072] This information is advantageous because it reveals, for example, that rework is necessary at one or more points on workpiece 8.

[0073] If the threshold is not met, the feed rate, acceleration and / or jerk will be increased, as explained above.

[0074] FIG 4 An exemplary implementation of the process. The figure shows a tracking method for achieving a user-specified machining quality.

[0075] User specifications 100 are shown in the figure, specifying the path G0, G1, feed rate F, spindle speed n, and target quality factor, typically in the form of a part program. Furthermore, the defined deviation Ad and, advantageously, another defined deviation Ad2 are specified.

[0076] The control system 2 advantageously analyzes the deviation from specified target position values ​​Xsoll, Ysoll, Zsoll, Asoll and Csoll (target values ​​of the five axes) and actual position values ​​Xist, Yist, Zist, Aist and Cist (actual values ​​of the five axes) measured on the measuring system, both axis- and path-related.

[0077] A comparison of target speed with actual speed or target acceleration with actual acceleration is achieved analogously to the method shown, based on the comparison of target position values ​​with actual position values.

[0078] This analysis may also include a discrepancy between commanded and measured speed or acceleration.

[0079] Advantageously, both the rotary encoders or linear scales installed in the machine are used to record position values, as well as additional sensors arranged close to the TCP (tool side) or the workpiece (tool side) to measure speed or acceleration.

[0080] Based on the analysis of predefined target and actual values, control unit 2 generates a key performance indicator (KPI) for determining the quality of a finishing operation. This KPI is the actual quality value, Gist. To determine the actual quality value, Gist, signal processing of the target and actual values ​​is performed in the time and / or frequency domain. This is achieved in the quality calculation block, Gb.

[0081] Using the example of positional values, a difference signal between target and actual positional values ​​is advantageously determined over a specific period, e.g., 1 second. This difference signal is then advantageously subjected to standard signal analysis methods. These methods are based, for example, on well-known techniques such as averaging, calculating a standard deviation, and / or frequency analysis.

[0082] The standard deviation of the difference signal can, for example, serve as a measure of the actual quality factor (Gist). However, in addition to the standard deviation, other parameters from signal analysis can also be incorporated (so).

[0083] In addition to the difference signal between target and actual position values, alternative or additional difference signals between target and actual speed or target and actual acceleration can also be analyzed and incorporated into the actual quality value according to the signal analysis mentioned above.

[0084] The described signal analysis is advantageously performed analogously for further, preferably all, axes, as well as advantageously for the TCP, and is advantageously incorporated into the quality score, for example by means of a weighting.

[0085] For the quality factor, the user specifies a target value in the diagram. This is the target quality value, Gtarget. Gtarget can either be programmed in the part program or entered via control 2.

[0086] Different materials require different quality target values ​​to achieve good machining. The quality target value is advantageously a value based on experience (especially through analysis of workpiece surfaces) from previous similar machining operations.

[0087] For example, the target quality value Gsoll can be determined by considering several workpiece surfaces, where a target quality value present during machining has been determined according to the method described above and is therefore known, and the workpiece surfaces of the workpieces considered have been found to be good.

[0088] In this way, the target quality value Gsoll can be determined.

[0089] In the method shown, the controller 2 modifies the dynamic parameters jerk rmax and acceleration amax of the controller to adjust the actual quality value Gist to the target quality value Gsoll (see dynamic tracking Dy). 2. In dynamic tracking (Dy), it is checked whether the defined deviation Ad is exceeded. It can also be checked whether the defined deviation is not exceeded, or whether a further defined deviation is not exceeded.

[0090] As a consequence, the method advantageously allows essential parameters of a speed control Gf of the control 2 to be continuously adjusted.

[0091] Instead of continuous tracking, it is also possible to switch to another set of dynamic parameters. In this way, the required surface quality can be achieved.

[0092] If the control system 2 is able to determine the maximum possible feed rate by evaluating machining parameters, then in addition to modifying jerk rmax and acceleration amax, the feed rate Fmax can also be modified with the aim of achieving maximum productivity at a given quality.

[0093] Increasing rmax and amax as well as Fmax when the defined deviation Ad or the further defined deviation Ad2 of the actual quality value from the target quality value is undershot is advantageous for shortening a throughput time.

[0094] The invention offers the advantage that the control system can detect machining situations that would lead to a reduction in machining quality. This can be rectified immediately, advantageously in real time, using the described method. Alternatively, information about this can be stored so that rework can be carried out.

[0095] However, it is advantageous to react promptly to ensure processing quality by modifying the dynamic parameters.

[0096] A control-integrated algorithm that increases the dynamics and also the (feed) speed, provided the quality criterion is met and a tool allows this, is also advantageous.

[0097] FIG 5 shows a suitable arrangement of means for recording actual location values.

[0098] The figure shows a rotary encoder for the Y-axis 1001, a rotary encoder for the X-axis 1002 and a rotary encoder for the Z-axis 1003.

[0099] Preferably, a linear scale for the X-axis 1004 is arranged at and near the location shown. Preferably, a linear scale for the Z-axis 1005 is arranged at and near the location shown. Preferably, a linear scale for the Y-axis 1006 is arranged at and near the location shown.

[0100] The figure also shows the axes of rotation A and C. These allow the workpiece to be tilted (e.g. by means of a rotary-swivel table).

[0101] This tilting can also be detected by linear scales 1010, 1011, 1012 or by rotary encoders 1007 or alternatively or additionally 1008 (A-axis) and 1009 (C-axis).

[0102] FIG 6 shows another possible tool and / or production machine 3 for which the invention is suitable.

[0103] In this embodiment, the machine tool and / or production machine 3 has six machine axes X, Y, Z, A, B, C, through which a relative movement can be carried out between the tool 6, which in this embodiment is in the form of a turning tool, and a workpiece 8. In this figure, the tool 6 is clamped in a tool holder 62, which is connected to a tool spindle 63, which in this embodiment is driven by a position-controlled motor 64.

[0104] Tool 6 can be advantageously moved translationally along the X, Y and Z axes.

[0105] The figure also shows rotary axes A and B, with which the tool 6 can be rotated around the respective axis and also aligned in a position-controlled manner by the angular positions α and β relative to the workpiece 8.

[0106] Furthermore, in this embodiment, machine 3 has a third position-controlled rotary axis C, which runs parallel to the Z-axis and with respect to which the worktable 7 is rotatably mounted relative to a stationary machine frame 65. This allows the workpiece 8 to also be positioned in an angular position γ relative to the tool 1.

Claims

1. Method for operating a machine tool and / or production machine (1) with the following steps: - comparing at least one target position value (Xtarget, Ytarget, Ztarget, Atarget, Ctarget) of a machine axis (A, B, C, X, Y, Z) and / or a tool centre point (61) with an actual position value (Xactual, Yactual, Zactual, Aactual, Cactual) and / or - comparing at least one target speed of the machine axis and / or the tool centre point (61) with an actual speed and / or - comparing at least one target acceleration of the machine axis and / or the tool centre point (61) with an actual acceleration, - forming at least one actual quality value (Gactual) on the basis of the comparison or comparisons, wherein a difference signal is ascertained from the target position values and the actual position values and / or from the target speeds and the actual speeds and / or from the target accelerations and the actual accelerations over a specific period of time and the difference signal is fed to a signal analysis method, wherein variables determined using the signal analysis influence the actual quality value (Gactual), - comparing a target quality value (Gtarget) with the actual quality value, - reducing a feed speed (Fmax) and / or acceleration (amax) and / or jerk (rmax) of the machine axis (A, B, C, X, Y, Z) and / or the tool centre point if a defined deviation (Ad) of the actual quality value (Gactual) from the target quality value (Gtarget) is exceeded or storing information about the fact that the defined deviation (Ad) of the actual quality value (Gactual) from the target quality value (Gtarget) has been exceeded if the defined deviation (Ad) of the actual quality value (Gactual) from the target quality value (Gtarget) is exceeded.

2. Method according to claim 1, with the following further step: - increasing a feed speed (Fmax) and / or acceleration (amax) and / or jerk (rmax) of the machine axis (A, B, C, X, Y, Z) and / or the tool centre point if the defined deviation (Ad) or a further defined deviation (Ad2) of the actual quality value (Gactual) from the target quality value (Gtarget) is fallen below.

3. Method according to one of the preceding claims, wherein the target quality value (Gtarget) and / or the defined deviation (Ad) and / or the or a further defined deviation (Ad2) are stored in a parts program and / or are entered into a control system (2) of the machine tool and / or production machine (1), in particular a numerical control system.

4. Method according to one of the preceding claims, wherein the actual position value (Xactual, Yactual, Zactual, Aactual, Cactual) and / or the actual speed and / or the actual acceleration are captured by means of at least one measuring system (10, 11).

5. Method according to one of the preceding claims, wherein a measuring frequency of the actual position value (Xactual, Yactual, Zactual, Aactual, Cactual) and / or the actual speed and / or the actual acceleration is at least 500 / s, at most 1500 / s, preferably at least 800 / s and at most 1200 / s, in particular 1000 / s.

6. Method according to one of the preceding claims, wherein the actual position value (Xactual, Yactual, Zactual, Aactual, Cactual) is captured by a rotary transducer arranged in or on the machine tool and / or production machine (1) and / or a linear scale arranged in or on the machine tool and / or production machine.

7. Method according to one of the preceding claims, wherein the actual speed and / or the actual acceleration is captured by at least one sensor (11), wherein the sensor is arranged on or close to the tool centre point (61) or on or close to a workpiece, which is machined by the machine tool and / or production machine.

8. Control system (2) for a machine tool and / or production machine (1) for performing the method according to one of claims 1 to 7.

9. Machine tool and / or production machine (1), having a control system or connected to a control system (2) according to claim 8, in particular a numerical control system.

10. Computer program product (21) comprising instructions, which, when the program is executed by the control system (2) according to claim 8, cause it to execute the method according to one of claims 1 to 7.