Patent Application
20210031329
The invention relates to a machining device, in particular a CNC machining device, for machining preferably plate-shaped workpieces, as well as a method.
Nowadays in the field of machining devices, a plurality of different machining possibilities must be must be offered and performed. I.e. the requirements placed on machining devices is often a split between machining processes in which a relatively small tool with a relatively high rotational speed is operated on the one hand, and on the other hand, machining processes in which a relatively large tool having a large mass and a large tool diameter is operated at a low rotational speed. For the small tools, a tool holding fixture is required which can be operated at very high rotational speeds (for example, 24,000 min−1). By contrast, for large tools, a high rigidity of the tool holding fixture is required which can absorb process forces such as, for example, bending torque, radial forces, cutting forces, etc. which are commonly very large at low rotational speeds. Since tool holding fixtures for high rotational speeds and tool holding fixtures for high process forces are generally dimensioned differently, there is a target conflict which means that the respective requirements can only be taken into account unsatisfactorily within the framework of compromise solutions. Additionally, the tools used are always becoming more powerful which, on the one hand, makes it possible to increase the rotational speed with even large tools having high process forces, yet on the other hand, this leads to the demands on the machining device increasing, in particular, with regard to resulting vibrations.
Accordingly, with known machining devices there is the problem that the tool holding fixture or the machining aggregate cannot be optimally designed for every tool, and accordingly, unwanted vibrations can occur in the tool holding fixture when machining a workpiece, in particular vibrations corresponding to the natural mode of the basic machine. This is particularly problematic with CNC machining devices in which the machining aggregate including the tool holding fixture is often suspended from multi-axis linear guides, which reduces the rigidity of the suspension and enables the vibrations generated to resonate up to a machine frame, in particular up to a machine bed of the machining device. This leads to an increased stress on the CNC machining device as well as the tool, and reduces the machining quality. The same problem applies to conventional pass-through machines since performance requirements also constantly increase with these.
For this reason, there is an effort to provide vibration-damping devices for machining devices, in particular for machining aggregates of CNC machining devices.
There are similar problems in the field of printing technology, textiles technology or newspaper press technology in which vibrations occur owing to the high rotational speed of, for example, pressure rollers or deflection shafts which can lead to damage to the bearings in the event of an superpositioning with the natural frequency. DE 10,2008,050,989 A1 therefore teaches, for example, to use a damped absorber to reduce vibrations of a hollow machine part such as a shaft, a roller or a mandrel. The damped absorber is composed of an additional mass and a damping and an elastic element. The additional mass is surrounded by a damping and elastic cylinder-shaped layer. In order to achieve the required parameters such as rigidity and damping coefficient with a predetermined additional mass and a certain main system, a defined pressure must be exerted on the elastic and damping layer. This makes a particular construction necessary which allows the absorber to integrate into a cylinder-shaped main system, such as for example, a mandrel.
Furthermore, active vibration-damping systems that are installed in the tool holding fixture are known from the field of machine tools. In the known active vibration-damping systems, the vibration amplitude of a vibration generated during the machining of a workpiece is detected by means of an acceleration sensor directly attached to the tool holding fixture, and a counter pulse corresponding to the detected vibration amplitude is generated by means of an electrodynamic actuator. However, this requires for each spatial direction in which the one vibration compensation is supposed to occur, the installation of an acceleration sensor as well as an electron-dynamic actuator, as well as the provision of a complicated controller for vibration compensation. This leads to high acquisition costs for such a type of vibration-damping system, which in many cases makes it economically uninteresting. Furthermore, the use is limited to larger machining devices due to the necessary actuators since otherwise the dead weight of the actuators influences the inertia mass of the machining aggregate too much.
The object of the present invention is therefore to provide a machining device, in particular a CNC machining device for machining preferably plate-shaped workpieces, with which the vibrations on a machining aggregate can be cost-effectively damped by means of a simple design.
The object is solved by a machining device according to claim 1 as well as a method according to claim 12. Preferred further developments of the invention are given in the dependent claims.
One of the core ideas of the present invention is to passively damp, in particular to absorb and to passively damp, vibrations of a dynamic element of a machining aggregate, in particular of a rotating tool spindle, which occur during the machining of a workpiece, by means of a vibration-damping device.
Using the proposed vibration-damping device, it is possible by means of a simple device design to passively damp the vibrations of a dynamic element of a machining aggregate, in particular of a rotating tool spindle, which occur during the machining of a workpiece, in a cost-effective manner. This eliminates the need for complicated control of an active damping element and the sensors and actuators needed for this, drastically reducing the manufacturing cost of the proposed vibration-damping device compared to known systems as well as the complexity.
According to the present invention, the machining device, in particular the CNC machining device for processing preferably plate-shaped workpieces which are preferably made at least in sections of wood, wood material, synthetic material and/or glass, has a machining aggregate with a dynamic element which preferably comprises a rotating tool spindle, a first guide assembly by means of which the machining aggregate can be moved in at least one spatial direction, and at least one vibration-damping device, wherein by means of the at least one vibration-damping device, vibrations of the dynamic element can be passively damped. The workpieces to be machined can also be rod-shaped or cubic workpieces as well as free-form bodies and the like.
In this manner, a vibration-damping device is provided with which, for example, with a CNC machining device as a specific example of a machining device, in a simple and cost-effective manner, vibrations of a dynamic element, in particular of the tool spindle of the machining aggregate of the CNC machining device, which occur in particular during the machining of a workpiece can be passively damped.
According to one embodiment of the present invention, the at least one vibration-damping device is provided on the side of the guide assembly facing the dynamic element or on the first guide assembly itself.
The vibration damping device provided thereby is particularly capable of damping the vibrations as closely as possible to the point of origin of the vibrations. Owing to the fact that the vibration-damping assembly is provided on the side of the first guide assembly facing the dynamic element, vibrations occurring can be damped even before reaching the first guide assembly. This prevents the propagation of vibrations and the associated vibration due to resonance.
According to an embodiment of the present invention, the at least one vibration-damping device of the machining device preferably is a vibration-absorbing device (damped absorber) which comprises at least one damping element, one auxiliary mass, and one elastic support member. This makes it possible not only to damp the dynamic element passively, but also to absorb and passively damp the resulting vibrations.
Here the elastic support element can carry the at least one damping element and the auxiliary mass, with preferably the elastic support member being fastened directly to the dynamic element or to the first guide plane. It is also possible to attach the at least one damping element to the auxiliary mass.
In general, passive vibration dampers/absorbers are known from the field of skyscraper and bridge construction such as, for example, the Millennium Bridge in London, the Rhine Bridge in Kehl-Strasbourg, as well as the skyscraper Taipei 101 in Taiwan. In principle, a damping element is accommodated in an elastic support member (for example, a housing) and is positioned to a dynamic element (for example, high-rise building). The damping element thereby remains in position and does not resonate with the critical frequency of the dynamic element (for example, the vibration of a high-rise building in the event of an earthquake), the elastic support member is equipped with a correspondingly large auxiliary mass. This auxiliary mass causes the elastic support member together with the damping element to remain in its intended position due to the inertia of the auxiliary mass, and accordingly enables the damping element to exert a damping force (damping effect) on the dynamic element. Specifically, this means that the dynamic element (also called vibration exciter) vibrates at a relatively high critical frequency within the elastic support member, whilst the elastic support member including the auxiliary mass vibrates with a relatively low frequency without becoming excited by the critical frequency.
If the elastic support member is secured directly to the dynamic element, it is necessary that the elastic support member has a sufficiently high elasticity to prevent an excitation of the auxiliary mass at the critical frequency of the dynamic element. However, there is the possibility thereby of arranging the vibration-damping device very compactly and very close to the point of origin of the vibrations. This makes it possible to damp the resulting vibrations before they propagate over wide areas of the machining device and, possibly, an increase in vibration builds up due to resonance. Since, as a rule, the connection between machining aggregate and guide assembly is formed extremely rigidly, a sufficiently high elasticity of the support member is also required in a case when the elastic support element is secured to the guide assembly.
Preferably the damping force of the at least one damping element directly acts on the dynamic element or the damping force of the at least one damping element indirectly acts on the dynamic element. Indirect in this context means that the at least one damping element acts, for example, on a suspension part by means of which the dynamic damping element or the machining aggregate comprising the dynamic damping element is fastened to the guide assembly. I.e. the damping force of the at least one damping element, for example, engages the suspension part and thus indirectly damps the vibration of the dynamic element.
According to one preferred embodiment of the present invention, the at least one damping element can be configured in the form of a hydraulic shock absorber, a mechanical shock absorber, an eddy-current damper, an electro-mechanical converter material, a hydraulic damping gap or the like. Individual types will be discussed more specifically below.
Moreover, the first guide assembly can comprise a guide device which is preferably configured in the form of a linear guide. The guide device can thereby have a guide carriage to which the machining aggregate including the dynamic element is secured in order to moveably guide the machining aggregate in a spatial direction, with the spatial direction being anywhere in space. Such guide devices are used, in particular, with CNC machining devices as well as pass-through machines in order to preferably be able to move the tool in all three spatial directions. However, guide devices have the disadvantage of reducing the rigidity of the suspension of the machining aggregate which makes the suspension more susceptible to vibrations, especially the build-up of increased vibrations. Since the vibration-damping device according to the present embodiment is, however, on the side of the guide assembly facing the dynamic element, the vibrations can be absorbed and damped before they reach the guide assembly.
According to the present invention, there is also the possibility to provide the vibration-damping device on the guide carriage of the guide device with which the vibration-damping device is still on the side of the guide device facing the dynamic element. By contrast, guide rails of the guide device and a machine frame to which, for example, the guide rails are attached, are arranged on the side of the guide device facing away from the dynamic element. Due to this assembly, it is possible to bring the center of mass of the vibration-damping device closer to the guide device and to consequently influence the inertia of the machining aggregate less. However, on the other hand, the critical vibrations of the dynamic element can only be damped indirectly since the damping force of the at least one damping element does not directly engage the dynamic element.
According to one further preferred embodiment of the present invention, it is possible to integrate the vibration-damping device into the tool spindle of the machining aggregate. Therefore, using this configuration, the vibration-damping device is directly built into the dynamic element. In this case, the tool spindle has a cylinder-shaped inner part and a hollow cylinder-shaped outer part, with the outer part being mounted on the inner part. With this design, the cylinder-shaped inner part corresponds to the dynamic element (vibration exciter) and the hollow cylinder-shaped outer part to the auxiliary mass and contains the damping element. Owing to the usually limited installation space, the design of the damping element in the form of a hydraulic damping gap is therefore ideal.
Moreover, it is preferred that the mass of the auxiliary mass and/or the damping characteristic of the damping element and/or the rigidity of the elastic support member is/are adjustable. It is particularly preferred that the respective adjustment is adjustable corresponding to the machining parameters such as, for example, feed rate, cutting speed, cutting depth, cutting force, rotational speed of the tool, and/or type of tool used, and/or measured vibration data, etc. This offers the advantage that the absorption and passive damping can be optimally adjusted to the occurring vibrations, in particular the adjustment can be made in such a way that a closer frequency range around the natural mode of the basic machine is particularly damped, whereby a resonance with the natural mode of the basic machine can be avoided. The basic machine is to be understood as the part of the machine which is located on the side of the guide assembly facing away from the dynamic element. The adjustment can thereby occur manually, mechanically or motorized. In particular as regards the adjustment of the damping characteristics of the damping element, the use of an eddy-current damper or an electro-mechanical converter material is ideal, since its damping force is purely electro-mechanically adjustable. The damping characteristic is to be understood as the applicable damping force, the damping constant (how fast the damper can follow the vibration), linear or progressive dampers and the like.
It is further preferred that at least two vibration-damping devices are provided which have two different directions of action that are on a shared plane. The vibration-damping devices are particularly preferably arranged around the dynamic element, which enables a compact design. If the machining device is provided with two vibration-damping devices which act on a shared plane in different directions, it is possible to damp the occurring vibrations in two spatial directions, which in sum increases the damping effect, especially if the direction of the occurring vibration amplitudes changes due to machining parameters.
According to a further preferred embodiment, the machining device is provided with three vibration-damping devices which have three different directions of action, and are on two intersecting planes. Furthermore, particularly preferably the three vibration-damping devices are arranged around the dynamic element.
In this manner, it is possible to damp vibrations occurring in three spatial directions.
Moreover, the present invention relates to a method for operating a machining device, in particular for operating a machining device as described above, wherein by means of the method, vibrations of a dynamic element of a machining aggregate, which in particular comprises a rotating tool spindle, which arise or occur during the machining of a workpiece, are passively damped, in particular absorbed and passively damped, by means of a vibration-damping device.
According to one preferred embodiment of the present invention, the method further comprises: determining machining parameters such as, for example, feed speed, cutting speed, cutting depth, cutting force, rotational speed of the tool, tool type, etc., and/or determining vibrations occurring from the dynamic element, preferably by means of vibration sensors, determining optimal setting parameters of the vibration-damping device such as, for example, the mass of the auxiliary mass, damping characteristics of the damping element, rigidity of the elastic support member, etc. and adjusting the optimal setting parameters of the vibration-damping device.
The determining of the optimal setting parameters of the vibration-damping device can thereby occur based on the determined machining parameters and/or the determined occurring vibrations, with preferably the determined machining parameters and/or the determined occurring vibrations being compared to empirically determined values and/or compared to values determined by means of simulations, and determined corresponding to the optimal setting parameters.
In this way, for example, the critical frequency, the natural frequency (natural mode) of the basic machine, can be determined which is largely constant regardless of the respective tool used and the respective machining parameters. Subsequently, different tools can be operated at different machining parameters in adjustment mode and the resulting vibrations can be measured in the test setup. In accordance with the measured vibrations, optimal setting parameters can then be detected and tested. The determined, optimal setting parameters can then be stored in a database which a standard machine can access, taking into account the tool used and the respective machining parameters, and corresponding to the setting parameters (such as, for example, mass of the auxiliary mass, damping characteristics of the damping element, rigidity of the elastic support member), the vibration-damping device can be automatically adjusted.
The adjustment of the optimal setting parameters can thereby preferably be carried out manually, motorized or electro-mechanically.
In the following, preferred embodiments of the present invention are described with reference to the accompanying drawings. Further variants and modifications of individual features cited in this context can each be combined with one another in order to form new embodiments.
Vibrations can be caused by the rotation of the tool spindle (4) together with the tool, for example, due to an unbalance at the tool spindle (4) or the tool owing to changing loads on the tool during the machining of a workpiece and the like.
As is also revealed by
The auxiliary mass (8) is constructed modularly, i.e. the auxiliary mass (8) consists of individual weight plates that can be modularly secured to the holding bracket in order to adjust the mass of the auxiliary mass in accordance with the operating parameters and/or the measured vibration data.
In the embodiment shown in
In the following, different embodiments of the vibration-damping device (6) of the present invention in its basic structure will be explained by means of schematic illustrations that are shown in
In turn,
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016210233.8 | Jun 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/063955 | 6/8/2017 | WO | 00 |
