METHOD FOR CONTROLLING A PROCESS

Description

[0001] The present invention relates to a method for controlling a machining process in which ultrasonic machining is carried out using a sonotrode that can be positioned against a workpiece.

[0002] In such machining processes, a sonotrode controlled by a generator generates ultrasound to weld, separate, seal, emboss, or similarly weld plastic workpieces together. In these machining processes, the sonotrode is positioned against the workpiece(s) and controlled by a generator to generate ultrasound. The generated ultrasound causes the material of the workpieces to melt, so that they can be welded, separated, embossed, sealed, or cut.

[0003] For proper processing, it is important that the processing is not ended too early or too late. For example, if ultrasonic processing is switched off too early or too late in a welding process, the workpieces may be damaged or the quality of the weld may be unsatisfactory. In known processes, various criteria can therefore be linked together to end the processing or to transition to a subsequent step in the processing process. For example, a welding process can be ended after a specified time has elapsed, a specified power has been reached, a predetermined energy has been supplied, or after a specific welding path has been completed; these criteria can also be logically linked.The problem here, however, is that certain workpieces are subject to manufacturing tolerances, so that the specified criteria can lead to machining results that are unsatisfactory, depending on the workpiece.

[0004] A method for controlling a machining process according to the preamble of claim 1 is known from DE 10 2018 208 032 A1. WO 2008 / 031823 A1 discloses a method for quality monitoring during ultrasonic welding. EP 1 997 580 A1 describes a method and device for welding a busbar to cables using vibrations.

[0005] It is the object of the present invention to provide a method for controlling a machining process according to the preamble of claim 1, which leads to improved machining results in ultrasonic machining with the aid of a sonotrode that can be positioned against a workpiece, in particular when the workpieces are subject to manufacturing tolerances.

[0006] This problem is solved by the features of claim 1.

[0007] The method according to the invention for controlling a machining process in which ultrasonic machining is carried out using a sonotrode that can be positioned against a workpiece comprises the following steps: Establishing a first reference gradient and a second reference gradient for the course of a process parameter over time, recording the course of the process parameter during ultrasonic processing, repeatedly determining a first gradient and a second gradient of the course during the processing process, wherein the two gradients are determined spaced apart in time by a predetermined time offset (t), comparing the first gradient with the first reference gradient and comparing the second gradient with the second reference gradient during the processing process, in each case using a predetermined comparison criterion, transitioning to a subsequent step of the processing process, in particular ending the ultrasonic processing, if the predetermined comparison criterion is met in one comparison and in particular in both comparisons simultaneously.

[0008] In the method according to the invention, the course of a process parameter is recorded during ultrasonic processing. This can be, for example, the power of the sonotrode / time, the amplitude of the sonotrode / time, the energy supplied to the sonotrode / time, the temperature of the sonotrode / time or the contact force of the sonotrode / time. The power of the sonotrode / time is understood to be the power supplied to the sonotrode by a generator. The contact force of the sonotrode / time is understood to be the force with which the sonotrode is placed against the workpiece or workpieces by an actuator. According to the invention, the course of the process parameter is recorded during ultrasonic processing, i.e. stored, and in particular also shown on a display, in particular in real time.It can be advantageous if the process parameters are processed during, before or after recording, for example by smoothing and / or filtering.

[0009] Furthermore, during the machining process, i.e. during recording, both a first gradient and a second gradient of the curve are repeatedly determined, with the two gradients being determined at a predetermined time offset from one another. In order to be able to automatically determine when the curve has reached a point at which the machining process is to transition to a subsequent step, for example, is to be ended, according to the invention a first reference gradient and a second reference gradient are previously defined for the curve of the process parameter. This allows (repeatedly or continuously) the determined first gradient to be compared with the first reference gradient and the determined second gradient to be compared with the previously defined second reference gradient while the machining is taking place.According to the invention, these comparisons are each carried out using a predetermined comparison criterion, so that a subsequent step of the processing process can only be proceeded to if the predetermined comparison criterion is met in both comparisons at the same time.

[0010] With the method according to the invention, the termination of ultrasonic processing can be individually adapted to the respective component, which may be subject to manufacturing tolerances. This is made possible by the fact that no, or only limited, rigid switch-off criterion that is independent of the actual machining process (such as time, distance, force or energy of the sonotrode or a tool) is specified. Instead, the course of the process parameter is checked during machining of the workpiece and the next step of the machining process is then progressed to when the previously defined reference gradients are reached at two points in time spaced apart from one another along the process parameter curve. This makes it possible to determine particularly reliably when the curve of the process parameter has reached a characteristic point, for example an inflection point.For example, if two workpieces are welded together, the sonotrode power curve over time reaches a maximum when both workpieces are completely melted. At this point, the machining process can or must proceed to a further step. This could include switching off the sonotrode, lifting the sonotrode from the workpiece, reducing the contact force with which the sonotrode is applied to the workpiece, or reducing the sonotrode power.

[0011] Of course, the method according to the invention can also be combined with conventional shutdown criteria, for example, the achievement of absolute values ​​of the displacement, time, force, energy, amplitude, or the like, of the sonotrode or machining tool used. It can also be advantageous to specify predetermined permissible deviations for the reference gradients, for example, deviations of + / -5% or the like.

[0012] According to an advantageous embodiment, the predefined comparison criteria can be selected from a group comprising: ≥, ≤, =, >, <. In this way, the method can be individually adapted to a particular process parameter profile, since the way in which the first gradient and the second gradient should correlate with the respective reference gradient can be individually set. For example, it can be specified that the determined first gradient must be greater than or equal to the first reference gradient, or it can be specified, for example, that the second determined gradient must be equal to the second reference gradient.

[0013] According to a further advantageous embodiment, the time period used to determine the first and / or second gradient can be specified, allowing even better adaptation to the course of the process parameter. For example, if the two time periods are selected to be different, abrupt changes in the course can be easily detected and used for control purposes.

[0014] Furthermore, it can be advantageous to proceed to the subsequent step of the processing process with a predetermined time delay.

[0015] This also allows the individual requirements of different processing processes to be addressed.

[0016] According to a further advantageous embodiment, the recording of the process parameter curve and the comparison of the gradients during ultrasonic processing can be carried out in real time, for example, with a sampling rate of 1 to 10 milliseconds, in particular 1 millisecond. This allows the process parameter to be recorded and evaluated very precisely.

[0017] According to a further advantageous embodiment, the first reference gradient and the second reference gradient can be determined by first carrying out ultrasonic machining of a workpiece, recording the profile of the process parameter, and determining the first reference gradient and the second reference gradient on the basis of the characteristics of the recorded profile. Since, according to the invention, the profile of the process parameters always differs for different machining processes and for different workpieces or workpiece pairs, the step described above can firstly be used to determine what the basic profile of the process parameter is. This can be used to determine, for example, maxima or inflection points of the profile, whereupon the two reference gradients can then be suitably set in order to switch off or on as desired.To trigger the processing process to advance.

[0018] According to a further aspect of the present invention, it relates to a process control device for controlling an ultrasonic machining process of the type described above, wherein the process control device is configured and designed to carry out a method of the type described above. Such a process control device can, for example, have a computing unit and an input / output unit, wherein the output unit can, in particular, display the profile of the process parameter in real time, and both the two reference gradients and the first and second determined gradients can be displayed in real time during machining.

[0019] The present invention is described below purely by way of example using an advantageous embodiment. Shown are: Fig. 1 shows a schematic representation of the course of a process parameter; Fig. 2 shows a schematic representation of an input device for a process control device; and Fig. 3 shows the representation of a course of a process parameter at an output device of the process control device.

[0020] As already described at the beginning, according to the invention, in order to control a machining process with a sonotrode, the course of a process parameter during ultrasonic machining is determined or recorded and, in particular, also displayed. Fig. 1 As an example of such a curve, it shows the ultrasonic power emitted by the sonotrode during processing over time. The visible graph corresponds to curve G, and the gradient m1 determined during processing results from the difference between the process values ​​at points 2 and 1, while the continuously determined gradient m2 results from the difference between the process values ​​at points 4 and 3. The two points in time at which the gradients of the graph and curve G are determined are spaced apart in time by a predetermined time offset Δt.

[0021] As described above, for the method according to the invention, reference gradients are first defined, namely a first reference gradient m1ref and a second reference gradient m2ref. Furthermore, the respective time periods t1 and t2 can be specified, which are used to determine the first and second gradients. Fig. 2 The illustrated embodiment shows part of an HMI input and output device with which various values ​​and criteria can be specified. In the illustrated example, 45 is selected for the reference gradient m1ref, and the reference gradient m2ref is set to 0. The time period t1 for determining the first gradient m1 is selected to be 35 milliseconds, while the time period t2 for determining the second gradient is selected to be 25 milliseconds. The time offset Δt is selected to be 15 ms.

[0022] Finally, the HMI input and output device can also define the comparison criteria to be applied when comparing the first gradient and the second gradient with the respective reference gradient. In the illustrated embodiment, the gradient m1 should be greater than or equal to the reference gradient m1ref of 45. The second gradient m2 should satisfy the comparison criterion V2 and be less than the second reference gradient m2ref of 0.0.

[0023] Fig. 3 shows a representation of an output device of a process control device according to the invention, wherein the power of the sonotrode is represented as the process parameter P over time. Both the first gradient m1 and the second gradient m2 are graphically (and mathematically) "placed" into the curve G, with the associated reference gradients m1ref and m2ref being simultaneously represented. At the process time shown, the gradient m1 is smaller than the gradient m1ref, so that the comparison criterion V1 of Fig. 2is not met. The same applies to the gradient m2, which is also greater than the specified reference gradient m2ref of 0.0. However, if the curve G continues to rise even more steeply and then drops abruptly, both gradients m1 and m2 meet the specified comparison criteria, i.e., the gradient m1 becomes greater than the gradient m1ref and the gradient m2 becomes equal to the gradient m2ref, so that the next step of the machining process can be continued; for example, ultrasonic machining can be terminated.

[0024] Even though the method described above was described in connection with a machining process that uses a sonotrode for ultrasonic machining, the method according to the invention can of course also be applied to other machining processes in which ultrasonic machining is not always carried out, for example, in joining processes, press-fitting processes, cutting processes, or the like. The described invention therefore expressly also extends to processes in which ultrasonic machining with the aid of a sonotrode is only carried out temporarily.

Claims

1. Method for controlling a machining process in which ultrasonic machining is carried out using a sonotrode which can be placed against a workpiece, comprising the following steps: - recording the progression (G) of the process parameter (P) during the ultrasonic machining, - repeatedly determining a first gradient (m1) and a second gradient (m2) of the progression during the machining process, the two gradients (m1, m2) being determined one after the other with a predetermined time offset (Δt), characterised by - defining a first reference gradient (mlref) and a second reference gradient (m2ref) for the progression (G) of a process parameter (P) over time (t), - comparing the first gradient (m1) with the first reference gradient (mlref) and comparing the second gradient (m2) with the second reference gradient (m2ref) during the machining process, in each case using a predetermined comparison criterion (V1, V2), - transitioning to a subsequent step of the machining process, in particular termination of the ultrasonic machining, if the predetermined comparison criterion (V1, V2) is met for both comparisons simultaneously.

2. Method according to claim 1, characterised in that the process parameter (P) is selected from a group comprising: power of the sonotrode / time, amplitude of the sonotrode / time, contact force of the sonotrode / time, energy supplied to the sonotrode / time, temperature of the sonotrode / time.

3. Method according to either claim 1 or 2, characterised in that the predetermined comparison criteria (V1, V2) are selected from a group comprising: ≥, ≤, =, > and <.

4. Method according to any of the preceding claims, characterised in that a time period (t1, t2) used for determining the first and / or second gradient is predetermined.

5. Method according to any of the preceding claims, characterised in that the transition to a subsequent step of the machining process is selected from a group comprising at least one of the following steps: switching off the sonotrode, lifting the sonotrode from the workpiece, reducing the contact force with which the sonotrode is placed against the workpiece, reducing the power of the sonotrode, reducing the feed rate of the sonotrode, changing the amplitude of the sonotrode.

6. Method according to any of the preceding claims, characterised in that the transition to the subsequent step of the machining process takes place with a predetermined time delay.

7. Method according to any of the preceding claims, characterised in that the recording of the progression of the process parameter (P) and the comparison of the gradients takes place in real time during the ultrasonic processing, in particular with a sampling rate of 1-10 ms.

8. Method according to any of the preceding claims, characterised in that the first reference gradient (mlref) and the second reference gradient (m2ref) are defined by initially carrying out an ultrasonic machining of a workpiece, recording the progression (G) of the process parameter in this context, and determining the first reference gradient (mlref) and the second reference gradient (m2ref) on the basis of the characteristics of the recorded progression.

9. Process control device for controlling an ultrasonic machining process using a sonotrode, set up and configured to carry out the method according to any of the preceding claims.

10. Process control device according to claim 9, characterised in that it has an input device (HMI) by means of which the reference gradients and the comparison criteria can be inputted.