Machine tool, in particular gear machining machine

Abstract

The invention relates to a machine tool, in particular a gear machine, having a rotary shaft, which has a receptacle in which a tool or a workpiece can be clamped, the shaft being driven by a drive, the machine tool having a controller for actuating the drive. In this case, the control device has a function for monitoring and / or checking the clamping state of the tool or the workpiece holder, said monitoring and / or checking being carried out by determining and evaluating at least one parameter of the drive of the shaft.

Description

Technical Field

[0001] The invention relates to a machine tool, in particular a gear cutting machine, having a rotating shaft with a receptacle for clamping a tool or a workpiece, wherein the shaft is driven by a drive. Background Art

[0002] Correct clamping of the tool or workpiece in the corresponding receptacle of the machine is essential for safe operation of the machine. Incorrect clamping, especially too low a clamping force, can lead to significantly worse machining results or even considerable damage to the axis, machine and / or balancing system.

[0003] However, since the clamping force cannot usually be determined directly, the clamping state cannot be checked immediately. Summary of the invention

[0004] An object of the present invention is to provide an improved machine tool.

[0005] The object of the present invention is achieved by a machine tool according to the present invention. Preferred embodiments of the present invention will be given in the following description.

[0006] The invention comprises a machine tool, in particular a gear cutting machine, having a rotating shaft with a receptacle for clamping a tool or a workpiece, wherein the shaft is driven by a drive, wherein the machine tool has a controller for controlling the drive. The monitoring and / or checking function is to monitor and / or check the clamping state of a tool or a workpiece holder by determining and evaluating at least one parameter of a drive of the axis.

[0007] The inventors of the present invention have realized that an insufficient clamping state of a shaft can be detected by evaluating the parameters of the drive of the shaft. Therefore, it is not necessary to measure the clamping force directly, but the clamping state can be recognized indirectly by the characteristics of the drive. In particular, such monitoring and / or checking can be performed without additional sensors by means of existing sensors of the drive.

[0008] According to one possible embodiment of the invention, the shaft has a manual clamping system. For example, a chuck is provided in the spindle or the bearing, which generates the clamping force by manual operation. The invention has particular advantages in this regard, because in the case of manual clamping, it is currently not possible for the machine controller to detect or monitor the clamping force.

[0009] However, the invention can also be used for axes with an automatic clamping system, but here too there are other options for monitoring the clamping force.

[0010] The function is designed in particular to be able to detect an insufficient clamping state. In particular, an insufficient clamping state can be a clamping state that is not clamped with sufficient clamping force. Such an insufficient clamping state can lead in particular to a significant heating of the drive. Inadequate clamping states of the tool and / or workpiece can lead in particular to unstable states in terms of control technology, which can lead to considerable power losses and thus to heating. In addition, the support surface of the tool and / or workpiece may not lie flat against the mating support surface of the receptacle and / or the tool and / or workpiece may not be oriented exactly colinearly with the axis.

[0011] According to a possible embodiment of the invention, the shaft has an automatic balancing system. The invention is particularly advantageous for this, since it is particularly susceptible to damage due to incorrect clamping.

[0012] According to one possible embodiment of the invention, the function determines and evaluates parameters of the drive that are related to the vibration characteristics of the shaft in order to detect an insufficient clamping state. The inventors of the present invention have recognized that by evaluating the vibration characteristics of the shaft, an insufficient clamping state can be detected. In particular, an aggravation of the vibration of the shaft in an insufficiently clamped state can be prevented thereby, since a vibration tendency of the shaft caused by an insufficiently clamped state can be detected by such a check and / or monitoring.

[0013] According to a possible embodiment of the invention, the function determines and evaluates frequency-dependent parameters of the drive of the shaft in order to identify an insufficient clamping state. In particular, the function determines and evaluates frequency-dependent parameters of a vibration characteristic of the shaft in order to identify an insufficient clamping state.

[0014] According to a possible embodiment of the invention, the function evaluates the parameter in a predetermined frequency range. It is taken into account that generally not all frequency ranges are of equal significance.

[0015] According to a possible embodiment of the present invention, at least one limit value of the evaluated frequency range can be predefined in an operator interface of the controller, which enables the function to be adapted to the corresponding machine.

[0016] According to a possible embodiment of the invention, the detection of the parameter is carried out at a predetermined basic speed of the shaft. However, the basic speed at which the detection is carried out is not decisive for the evaluation. Preferably, noise is superimposed on the basic speed for the measurement.

[0017] According to a possible embodiment of the invention, the function checks whether a parameter exceeds a limit value. The inventors have recognized that this relatively easy-to-implement method is sufficient to detect an insufficient clamping state.

[0018] According to a possible implementation of the present invention, the limit value may be predefined in an operator interface of the controller.

[0019] According to a possible specific embodiment of the present invention, the control unit has a shaft regulator for regulating the shaft speed.

[0020] According to one possible specific embodiment of the invention, the function determines a parameter of a vibration behavior of the shaft whose speed is regulated.

[0021] According to one possible embodiment of the invention, the actual speed signal of the drive is included in the evaluation performed by the function. In this case, the actual speed is determined in any case in the axis whose speed is regulated, and a corresponding signal is therefore provided in the axis controller. In this case, in particular, the actual speed signal is decomposed into its frequency components within the scope of the evaluation.

[0022] According to one possible embodiment of the invention, the function determines and evaluates parameters of a transmission characteristic of a speed control system of a shaft controller. Such a transmission characteristic in particular allows conclusions to be drawn about the vibration behavior of the shaft.

[0023] According to a possible implementation of the present invention, the relationship between the target current and / or target torque of the driver and the actual speed is determined. The inventors have recognized that the relationship between a target current and / or a target torque of a drive and the actual rotational speed allows particularly good inferences about the vibration behavior of the shaft and can reliably detect an insufficiently clamped state.

[0024] In particular, a relationship between a target current and / or a target torque of the drive and the actual rotational speed is determined for different frequencies, in particular for different excitation frequencies.

[0025] According to a possible specific embodiment of the invention, the function detects and evaluates a frequency response of the speed control system.

[0026] According to one possible embodiment of the invention, the function determines the parameters of the axis in a measuring sequence. The detection is therefore not carried out during the continuous operation of the axis, but preferably in a separate measuring sequence before the start of the operation.

[0027] According to one possible embodiment of the invention, the parameter is a frequency-dependent parameter and the function determines the parameter by exciting the shaft at different frequencies.

[0028] According to a possible specific embodiment of the invention, the excitation is performed by switching in a signal related to the target torque of the drive, in particular a signal having a plurality of frequency components, in particular by switching in noise.

[0029] According to a possible embodiment of the present invention, the function blocks further movement of the axis when an insufficient clamping state is detected, thereby preventing insufficient processing quality and machine damage caused by movement of insufficiently clamped tools and / or workpieces.

[0030] According to a possible implementation of the present invention, the function outputs an output on the operation interface of the machine tool when an insufficient clamping state is identified. In particular, the output may be to request the user to re-clamp the tool and / or the workpiece.

[0031] According to a possible implementation of the present invention, the function is designed so that the user must confirm re-clamping, and then the function checks the clamping state again.

[0032] According to one possible embodiment of the present invention, the user interface of the machine tool is designed to require the operator to indicate whether the tool and / or workpiece has been clamped before starting processing, wherein when the operator indicates that the tool and / or workpiece has been clamped, the function performs a clamping status check.

[0033] The invention can firstly be used for any machine tool. Preferably, the function is used for a tool holder.

[0034] The invention is particularly advantageously used in a gear processing machine, which may be, for example, a gear milling machine or a gear grinding machine.

[0035] The invention can be used in particular for gear machining machines in which the tool holder is arranged on a machining head which can be moved relative to the workpiece holder via a plurality of linear axes. Preferably, at least one linear axis is moved under NC control during gear machining in order to move the tool relative to the workpiece in order to form the toothing.

[0036] According to a possible embodiment of the invention, the tool or workpiece receptacle is a conical receptacle, in particular a hollow shaft conical receptacle or a steeply conical receptacle.

[0037] In one possible embodiment, the machine tool according to the invention is a gear grinding machine and / or a gear milling machine. For example, the controller can have a function for performing a rolling grinding process and / or a rolling milling process. The tool can be a grinding tool or a milling tool, in particular a grinding worm or a hobbing cutter.

[0038] The tool or workpiece can be clamped in the tool or workpiece receiving portion by one side or both sides. A counter holder is preferably provided here, which allows clamping on both sides.

[0039] In one possible embodiment, the tool or workpiece holder is designed so that the tool or workpiece can be clamped manually.

[0040] The execution of this function is preferably triggered by a preset trigger event queried by the controller. If this function is activated, it preferably performs detection and evaluation automatically.

[0041] In one possible embodiment, the controller comprises a microprocessor and a non-volatile memory on which a software program is stored. The software program contains instructions executed on the microcomputer, which perform the above-mentioned machine tool control and, in particular, implement the functions according to the invention on the controller. The controller is in particular in signal connection with at least one sensor of the axis and / or drive. In addition, the controller is preferably connected to a user interface.

[0042] The invention also includes a software program for a machine tool as described above, which has instructions which, when executed on a microprocessor of a control, carry out the control according to the invention and / or the function according to the invention by means of the control of the machine tool for monitoring and / or checking the clamping state of a tool or workpiece receptacle. In this case, the software program can in particular allow the function according to the invention to be implemented on existing machine tools.

[0043] The invention also includes a method for operating a machine tool, in particular a gear cutting machine, wherein the machine tool has a receptacle in which a tool or a workpiece can be clamped, wherein an axis is driven by a drive. The method comprises the following steps:

[0044] - determining at least one parameter of the axis; and

[0045] - Monitoring and / or checking the clamping state of the tool or the workpiece holder by evaluating the parameters.

[0046] In this case, the method can in particular be carried out as described above with respect to a machine tool. In particular, the method is carried out on a machine tool as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be described in detail below with reference to the accompanying drawings and according to embodiments.

[0048] Figure 1 An embodiment of a machine tool according to the invention is shown,

[0049] Figure 2 An embodiment of a shaft of a machine tool according to the invention is shown,

[0050] Figure 3 A schematic diagram showing an axis regulator of a controller of a machine tool according to the present invention is shown,

[0051] Figure 4 A graph showing the frequency response of the shaft at different tool diameters is shown.

[0052] Figure 5shows a graphical representation of the frequency response of the shaft at different clamping conditions at a first tool diameter, and

[0053] Figure 6 A graphical representation of the frequency response of the shaft at different clamping conditions at a second tool diameter is shown. DETAILED DESCRIPTION

[0054] Figure 1 and Figure 2 An embodiment of a machine tool and an axis of such a machine tool is shown, in which a preferred design of the present invention is used. In this embodiment, the machine tool is a gear processing machine. However, the function according to the present invention can also be used in other machine tools.

[0055] The machine tool has a machining head 1, on which a rotation axis B1 is arranged, by which a tool is rotated. The axis B1 has a tool holder 5, in which a tool can be clamped, and which is driven by a drive 8. In this case, the tool holder 5 is arranged directly on the shaft of the drive.

[0056] The machine also has an axis C2 which has a workpiece holder 3 which is driven by a drive 8 . The axis C2 is arranged on a bed 7 .

[0057] The machining head 1 can be moved via a linear axis X1 in a direction perpendicular to the C2 axis in order to move a tool accommodated in the tool holder towards a workpiece accommodated in the workpiece holder. The linear axis X1 thus defines the engagement depth. In addition, a linear axis Z1 is provided, via which the machining head can be moved along the width of the workpiece in a direction parallel to the C2 axis.

[0058] In this embodiment, the machining head can be pivoted about an A1 axis extending parallel to the X1 axis. In addition, the tool holder can be translated (vertical shift bar) via a linear axis V1 in a direction parallel to its rotation axis. Alternatively, the machine tool can also have a Y1 axis, which is perpendicular to the X1 axis and the Z1 axis, and the A1 axis is arranged on this Y1 axis.

[0059] Figure 2 An embodiment of a shaft B1 is shown in an enlarged view, which has a manually operated clamping system for clamping a tool.

[0060] exist Figure 2, a tool holder 5 with a chuck is shown. The tool holder can be, for example, a steeply tapered or hollow-shaft tapered holder. Manual clamping is achieved, for example, by a chuck arranged in the tool spindle, which is manually clamped, for example, by an Allen key. In this embodiment, the machining head has a counterholder 6 for the tool holder 5 in order to be able to clamp the tool on both sides. The counterholder is arranged movably along a linear guide parallel to the B1 axis. In addition, the axis B1 has an automatic balancing system.

[0061] In this embodiment, the control of the machine tool includes an axis regulator with a speed control device for the B1 axis. For this purpose, the axis and here preferably also the drive have a speed sensor, whose signal is fed back into the control system. In particular, the speed sensor is an angle measuring system or a rotary encoder. A corresponding regulator can also be used for the C2 axis.

[0062] Figure 3 The schematic diagram of such a shaft regulator with a control system for speed control is shown. Figure 3 As shown, a speed target value is preset for the shaft regulator, according to which the drive should be regulated. In addition, the drive also has a speed sensor, which is referred to as a motor sensor and detects an actual speed value. The actual speed value is fed back to the control system and compared with the speed target value in a differential mechanism. The speed regulator determines the torque target value of the drive based on the difference between the actual speed value and the speed target value, and a current target value is set in the current regulator based on the torque target value, which is used to control the motor.

[0063] In this exemplary embodiment, the function according to the invention for monitoring and / or checking the clamping state of a tool or workpiece holder determines a frequency-dependent parameter of a drive that is correlated with the vibration behavior of a shaft. In particular, the transfer behavior of the speed regulator in a measurement sequence at different excitation frequencies is determined and evaluated.

[0064] The speed control system and in particular the transmission path between torque and speed are first considered in more detail as the system to be regulated. The task of the speed control system is to regulate the motor speed. To this end, the speed control system outputs a torque and expects a speed change.

[0065] Whether the speed changes easily depends on the total inertia in the control system. If the inertia is high, the speed response is low. This means that the amplitude is low based on the speed / torque ratio. Conversely, the motor speed reacts particularly strongly at the resonant frequency. In addition, due to the dynamic feedback of the load on the motor, there are also damping frequencies that cause the motor speed to drop suddenly.

[0066] This feature can be found in e.g. Figures 4 to 6 The Bode plot of the speed control system used in the is clearly shown in the figure. The frequency response shown in the figure describes the frequency-dependent transfer characteristic of the speed control system, where the input signal is the torque and the output signal is the actual speed.

[0067] Here, the current actual value can also be measured instead of the torque target value or the current target value in order to identify only the mechanical part of the control system. The measured current can be easily converted into torque using the torque constant. In order to determine the representation, the signal is transformed into the frequency range.

[0068] In one embodiment, during the measurement process:

[0069] A) Regulator adjustments have been weakened

[0070] B) The axis runs at a constant rotational speed

[0071] C) Noise is added to the torque target value

[0072] D) The actual values ​​of motor speed and torque are measured.

[0073] E) The measurements were averaged and presented as a Bode plot.

[0074] The Bode diagram shows the measured transfer frequency response in the form of a logarithmic frequency.

[0075] The axis is excited, for example, with a noise signal, more precisely a PRBS (pseudo random binary sequence). This generates a signal similar to "white noise" that contains a large number of frequency components of equal magnitude (constant power spectral density). This allows the entire bandwidth of interest to be excited at once with one signal.

[0076] Such measuring channels are already implemented in many drive controllers, since the parameters of the controller can be optimized using the Bode diagram.

[0077] According to the invention, however, the measurement results are now evaluated by the controller in order to detect an insufficient clamping state.

[0078] Figures 4 to 6 The test measurement results on the spindle with different tool diameters and clamping forces are shown. The speed frequency response (target current (speed regulator output) relative to the actual speed) is shown respectively.

[0079] The frequency response therefore has an integrator behavior and in principle allows the 0 dB line to be exceeded without causing contour damage to the workpiece (the frequency response does not directly show the position characteristics). However, exceeding the 0 dB line is considered an indicator that excessive vibrations can be detected. However, this should only be evaluated from 300 Hz onwards, since even with normal clamping, exceeding is normal at lower frequencies.

[0080] In the frequency response shown, it must also be taken into account that the profile is greatly smoothed by a third-order Butterworth filter, the cutoff frequency of which is one quarter of the sampling frequency.

[0081] like Figure 4 As shown, the tool diameter does have a significant effect on the frequency response. However, in the presence of a correct clamping condition, for example at a clamping force of 11 kN mentioned in the present embodiment, beyond a given lower limit, for example 300 Hz, the value does not exceed the 0 dB line in any case.

[0082] on the contrary, Figure 5 and Figure 6 The diagram in Figure 1 shows the frequency response of two different tools at different clamping conditions. The results show that in the case of insufficient clamping (clamping force below 6 kN), the parameters of the resonance point exceed the 0 dB line. Therefore, this test shows that an incorrect clamping condition can be identified based on the frequency response.

[0083] The function of detecting an incorrect clamping state can be implemented as follows:

[0084] Configure the measurement process of the B1 axis (or spindle); and set parameters in the machine configuration to define the starting frequency of the search. Preferably, this starting frequency is variable here, but preferably only for technical service personnel.

[0085] Based on the measurement results, the controller selectively:

[0086] - In case of negative feedback: triggering an NC-fault message which requires user confirmation ("Please check tool clamping") and then taking the measurement again;

[0087] or

[0088] - In case of positive feedback: continue with the processing process.

[0089] Provision can be made here that in the event of several consecutive negative determinations, this cycle is interrupted by no longer displaying the above-mentioned error message to the user, but rather a message that the clamping state is not in compliance with the specification and that continuing with the current clamping state would entail risks. The operator must acknowledge this message before being able to proceed.

[0090] In addition, the evaluation results and confirmation of the fault report are logged in the controller.

[0091] The assessment can be done as follows:

[0092] -Analyze the measured data. Implement a smoothing filter and perform smoothing.

[0093] - Determine whether there is a value greater than 0 dB above the start frequency among the smoothed values.

[0094] - If yes, respond negatively to the NC's "inquiry". If no, respond positively to the NC's "inquiry".

[0095] For example, the following events can be defined as triggers for a function:

[0096] a. Tool change position (required)

[0097] b. Tool diameter change (optional)

[0098] c. Sensor signal after tool change (optional)

[0099] In this case, the operator is specifically asked whether a tool change has been carried out. If so, the function is triggered.

[0100] The execution of the measuring program is preferably carried out only when the door is closed. It is preferably carried out at a predetermined constant rotation speed of the shaft, which is superimposed with a noise signal.

[0101] When evaluating the measurement, the 0 dB line (optionally with a certain amplitude margin) can be used as a fixed limit value. Alternatively, the limit value can be variably predefined and / or parameterized in the machine controller.

[0102] If, according to the measurement results, insufficient clamping is detected and / or limit values ​​are exceeded, the axis is stopped and a message is issued which can only be confirmed by another successful measurement. The message preferably includes a request for a mechanical check and / or a display of parameters.

[0103] Exceeding limit values, in particular the 0 dB line, will be recorded with a time stamp.

[0104] The invention thus allows automatic detection of incorrect clamping states of tool and / or workpiece axes (B1 axis and / or C2 axis) on machine tools. In particular, incorrect clamping states of the tool interface on the grinding head can be detected reliably and automatically and inadmissible vibration aggravation of the B1 axis and / or C2 axis can be prevented. By stopping the axis in a defined manner, inadequate machining results and further secondary damages can be prevented, which often lead to high repair costs. The technical solution based on the frequency response measurement can also realize machine protection for other axes.

Claims

1. A machine tool, in particular a gear cutting machine, having a rotating shaft, the shaft having a receptacle in which a tool or a workpiece can be clamped, wherein the shaft is driven by a drive, wherein the machine tool has a control for controlling the drive, It is characterized in that The control unit has a function for monitoring and / or checking the clamping state of the tool or workpiece holder, wherein the monitoring and / or checking is performed by determining and evaluating at least one parameter of the drive of the axis.

2. The machine tool according to claim 1, wherein: The function determines and evaluates parameters of the drive which are correlated with the vibration behavior of the shaft in order to detect an insufficiently clamped state.

3. The machine tool according to claim 1 or 2, wherein: The function determines and evaluates frequency-dependent parameters of the drive of the shaft in order to detect the insufficient clamping state.

4. The machine tool according to claim 3, wherein: The function evaluates the parameter within a predetermined frequency range, wherein preferably at least one limit value of the evaluated frequency range can be predefined in a user interface of the control unit.

5. The machine tool according to any one of claims 2 to 4, wherein: The function checks whether the parameter exceeds a limit value, wherein the limit value can preferably be predefined in a user interface of the control device.

6. A machine tool according to any one of the preceding claims, wherein: The control unit has a shaft regulator for regulating the rotational speed of the shaft.

7. The machine tool according to claim 6, wherein: The function determines parameters of a vibration behavior of a speed-controlled shaft, wherein an actual speed signal of the drive is preferably included in the evaluation performed by the function.

8. The machine tool according to claim 6 or 7, wherein: The function determines and evaluates parameters of a transfer characteristic of a speed control system of the shaft regulator, in particular the relationship between a target current and / or a target torque of the drive and an actual speed, in particular a frequency response of the speed control system.

9. A machine tool according to any one of the preceding claims, wherein: The function determines parameters of the shaft in a measurement process, wherein the parameters are preferably frequency-dependent parameters, and the function determines the parameters by exciting the shaft at different frequencies, wherein the excitation is preferably performed by switching on a signal regarding a target torque of the drive, in particular a signal having multiple frequency components.

10. A machine tool according to any one of the preceding claims, wherein: The function blocks further movement of the axis upon detection of an insufficient clamping state and / or issues an output on a user interface of the machine tool, in particular, the output being a request to the user to retighten the tool and / or workpiece.

11. The machine tool according to claim 10, wherein: The function is designed so that the user must confirm the re-clamping, and then the function performs another check of the clamping state.

12. A machine tool according to any one of the preceding claims, wherein: The user interface of the machine tool is designed to ask the operator to indicate whether the tool and / or workpiece is clamped before starting machining, wherein when the operator indicates that the tool and / or workpiece is clamped, the function performs a check of the clamping state.

13. A machine tool according to any one of the preceding claims, wherein: The tool or workpiece receptacle is a conical receptacle, in particular a hollow shaft conical receptacle or a steeply conical receptacle.

14. A software program for a machine tool according to any one of the preceding claims, the software program having the following instructions: when the instructions are executed on a microprocessor of a controller, the instructions implement control of the controller of the machine tool and / or implement functions for monitoring and / or checking the clamping state of a tool or workpiece holder.

15. A method for operating a machine tool, in particular a gear cutting machine, in particular a machine tool according to any one of the preceding claims, wherein: The machine tool has a receptacle in which a tool or a workpiece can be clamped, wherein a shaft is driven by a drive, and the method comprises the following steps: - determining at least one parameter of said axis; and The clamping state of the tool or of the workpiece holder is monitored and / or checked by evaluating the parameter.

Images