Method for Detecting the Making or Breaking of Contact of a Sonotrode with a Counter-Element

Abstract

The present invention concerns a method of detecting the making or breaking of contact of a sonotrode (4) which is caused to vibrate with a frequency f and a vibration amplitude A.sub.0 with a counterpart element (5). To provide a method with which contact-making or breaking of a sonotrode with a counterpart element can be particularly quickly and inexpensively detected it is proposed according to the invention that the method has the following steps: a) recording a time configuration of the vibration amplitude A.sub.0 (1) during a first measurement time interval ΔT, and b) determining from the time configuration of the vibration amplitude A.sub.0 (1) whether making or breaking of contact occurred within the measurement time interval ΔT.

Claims

1. A method of detecting the making or breaking of contact of a sonotrode (4) which is caused to vibrate with a frequency f and a vibration amplitude A.sub.0 with a counterpart element (5), comprising the steps: a) recording a time configuration of the vibration amplitude A.sub.0 (1) during a first measurement time interval ΔT, and b) determining from the time configuration of the vibration amplitude A.sub.0 (1) whether making or breaking of contact occurred within the measurement time interval ΔT.

2. A method according to claim 1 characterised in that in step b) making or breaking of contact of the sonotrode (4) with the counterpart element (5) is established if the recorded vibration amplitude A.sub.0 differs from a predetermined reference amplitude R by more than a predetermined tolerance value α or if the recorded vibration amplitude A.sub.0 lies outside a predetermined tolerance interval [T.sub.min, T.sub.max].

3. A method according to claim 2 characterised in that before step a) during a second measurement time interval Δt a time configuration of the vibration amplitude A.sub.0 is recorded and the reference amplitude and/or the tolerance interval are calculated from the recording during the second measurement time interval Δt.

4. A method according to claim 3 characterised in that i) a mean vibration amplitude is calculated from the recording during the second measurement time interval Δt and the calculated mean vibration amplitude is used in step b) as the predetermined reference amplitude, and/or ii) a minimum vibration amplitude A.sub.min and a maximum vibration amplitude A.sub.max is determined from the recording during the second measurement time interval Δt and the tolerance interval is calculated from the minimum vibration amplitude A.sub.min and the maximum vibration amplitude A.sub.max with T.sub.min≤A.sub.min and T.sub.max≥A.sub.max.

5. A method according to claim 1 characterised in that in step a) the sonotrode (4) is excited by a converter, wherein the converter is connected to a current generator and the current I.sub.E(t) which is provided by the current generator and flows through the converter is measured, in which case the voltage U.sub.E(t) applied to the converter by the current generator is measured, and wherein the vibration amplitude or a field size related to the vibration amplitude of the electrical vibration system comprising the current generator and the converter is calculated from the measured voltage U.sub.E(t) and from the measured current I.sub.E(t).

6. A method according to claim 2 characterised in that the method has the following further step: c) determining a time t.sub.0 at which contact-making recorded in step b) occurs, from the time configuration of the vibration amplitude (1), wherein the time at which the vibration amplitude within the measurement time interval ΔT for the first time leaves a tolerance range [T.sub.min, T.sub.max] or [R−α, R+α] (3) or a time shifted from said time by a predefined correction time is established as the time t.sub.0 of contact-making.

7. A method according to claim 1 characterised in that in step a) a sampling rate for determining the time configuration of the vibration amplitude of at least 2000 samples/s.

8. A method according to claim 1 characterised in that a counterpart tool (5) is used as the counterpart element, wherein a material (7) to be processed can be arranged between the sonotrode (4) and the counterpart tool (5) and wherein contact-making of the sonotrode (4) with the counterpart tool (5) is detected.

9. A method of controlling an ultrasonic vibration apparatus according to claim 1, the apparatus having a sonotrode (4) and a counterpart tool (5) is used as the counterpart element and wherein the counterpart tool (5) is arranged in operation in opposite relationship with the sonotrode (4) in such a way that a material (7) for processing by the sonotrode (4) can be arranged between the sonotrode (4) and the counterpart tool (5), comprising the steps: A) exciting the sonotrode (4) with a vibration during a predetermined time duration t.sub.d, B) detecting contact-making of the sonotrode (4) with the counterpart tool (5), and C) terminating the excitation of the sonotrode (4) or moving the sonotrode (4) away from the counterpart tool (5) when in step B) contact-making between the sonotrode (4) and the counterpart tool (5) was detected.

10. A method according to claim 9 characterised in that step C) is carried out only after the expiry of a predefined follow-on time t.sub.N after detection of contact-making.

11. A method according to claim 7 characterised in that in step a) a sampling rate for determining the time configuration of the vibration amplitude of at least 5000 samples/s is used.

12. A method according to claim 11 characterised in that in step a) a sampling rate for determining the time configuration of the vibration amplitude of at least 15000 samples/s is used.

13. A method according to claim 10 wherein immediately after detection of contact-making a reduction in the vibration amplitude is implemented.

Description

[0065] Further advantages, features and possible applications of the present invention will be apparent from the description hereinafter of a preferred embodiment and the accompanying Figures in which:

[0066] FIG. 1 shows a diagrammatic view of a sonotrode and an anvil before contact-making (at the left) and upon contact-making, and

[0067] FIG. 2 shows a graph illustrating the time configuration of the vibration amplitude of a sonotrode when using an embodiment of the method according to the invention.

[0068] FIG. 1 shows a diagrammatic view of a sonotrode 4 and a counterpart tool 5. A material 7 to be severed is disposed between the sonotrode 4 and the counterpart tool 5. The counterpart tool 5 has a raised portion 6.

[0069] The situation immediately before processing is shown on the left-hand side of FIG. 1. To sever the material 7 the sonotrode 4 is moved in the direction of the counterpart tool 5. The material is compressed between the sonotrode 4 and the raised portion 6 until the sonotrode 4 and the raised portion 6 come into contact with each other, as shown at the right in FIG. 1. When the raised portion 6 comes into contact with the sonotrode 4 the material 7 is severed and the processing step is concluded. In the state shown at the right in FIG. 1 the making of contact between the raised portion 6 and the sonotrode 4 leads to a change in the vibration amplitude of the sonotrode 4, that is detected according to the invention.

[0070] FIG. 2 shows a two-axis graph in which time t is plotted on the horizontal axis and the vibration amplitude A.sub.0 is plotted on the vertical axis. The line identified by reference 1 consequently represents the time configuration 1 of the vibration amplitude A.sub.0.

[0071] The illustrated time configuration 1 of the vibration amplitude A.sub.0 involves the time configuration of the vibration amplitude of a sonotrode of an ultrasonic cutting apparatus, in which a method according to the invention for detection of contact-making between a sonotrode and a counterpart tool was used. In the basic cutting process a material was arranged between the sonotrode and the counterpart tool, and that material was then cut by the sonotrode by ultrasonic machining. The time configuration 1 shown in FIG. 2 illustrates the vibration amplitude A.sub.0 of the sonotrode from the moment in time at the beginning or initiation of the vibration used in that case of the sonotrode to the moment in time at which the vibration of the sonotrode ends.

[0072] The transient condition can be seen in the time configuration 1 of the vibration amplitude A.sub.0 in the left-hand region thereof, in which the vibration amplitude A.sub.0 of the sonotrode firstly rises steadily from a zero position before then in the central region of the graph it adopts a configuration in which it vibrates slightly about a fixed value, which shows that the transient condition is terminated.

[0073] In the time configuration of the vibration amplitude A.sub.0, shown in FIG. 2, an embodiment of the method according to the invention was used, which involves a delay time t.sub.d such that the measurement time interval ΔT only starts after the conclusion of the transient state. The time extent of the delay time t.sub.d is identified by a double-headed arrow in the FIG. 2 graph.

[0074] In addition the graph shown in FIG. 2 shows a tolerance range 3 defined by a reference amplitude R and a tolerance value α. The tolerance range 3 extends from a lower limit of the vibration amplitude R−α to an upper limit of the vibration amplitude R+α. The underlying method according to the invention provides that contact between counterpart tool and sonotrode is determined when the vibration amplitude leaves the tolerance range 3 within the measurement time interval ΔT, here therefore after the delay time t.sub.d, and thus assumes values greater than R+α or smaller than R−α.

[0075] It will be seen that at the location identified by reference 2 in the time configuration 1 of the vibration amplitude A.sub.0 the vibration amplitude A.sub.0, within the measurement time interval ΔT which began after the delay time t.sub.d, assumes a value outside the tolerance range 3 after it had previously still assumed a value within the tolerance range 3. The associated time t.sub.0 is consequently determined by the moment in time at which the vibration amplitude A.sub.0 lies for the first time outside the tolerance range 3. The time t.sub.0 is now determined as the moment in time at which contact has occurred between sonotrode and counterpart tool.

[0076] In the embodiment of the invention which forms the basis of the graph shown in FIG. 2 the ultrasonic vibration apparatus is shut down after a follow-on time t.sub.N as a reaction to the given contact occurring between counterpart tool and sonotrode, so that the vibration of the sonotrode ends. The follow-on time t.sub.N is also shown by a double-headed arrow in FIG. 2, starting from the time t.sub.0 at which the sonotrode and counterpart tool come into contact. In that respect the method forming the basis for the illustrated configuration 1 of the vibration amplitude A.sub.0 provides that the vibration amplitude is steadily decreased within the follow-on time t.sub.N. With the expiry of the follow-on time t.sub.N the vibration of the sonotrode ends within a very short period, within which the vibration amplitude falls to the zero position of the vibration amplitude.

[0077] To sum up: the present invention concerns a method of detecting the making or breaking of contact of a sonotrode (4) which is caused to vibrate with a frequency f and a vibration amplitude A.sub.0 with a counterpart element (5). To provide a method with which contact-making or breaking of a sonotrode with a counterpart element can be particularly quickly and inexpensively detected it is proposed according to the invention that the method has the following steps: a) recording a time configuration of the vibration amplitude A.sub.0 (1) during a first measurement time interval ΔT, and b) determining from the time configuration of the vibration amplitude A.sub.0 (1) whether making or breaking of contact occurred within the measurement time interval ΔT.

LIST OF REFERENCES

[0078] 1 time configuration of the vibration amplitude [0079] 2 location in the value range of the vibration amplitude [0080] 3 tolerance range [0081] 4 sonotrode [0082] 5 counterpart tool [0083] 6 raised portion [0084] 7 material [0085] R reference amplitude [0086] α tolerance value [0087] t.sub.d delay time [0088] t.sub.N follow-on time [0089] t.sub.0 moment in time [0090] t time [0091] A.sub.0 vibration amplitude (amplitude of the vibration of the sonotrode)