Method for cutting a process material under the application of ultrasonic energy as well as cutting device

Abstract

The method serves for operating a cutting device, which is designed for cutting a process material, particularly foodstuff and which has at least one blade, which is driven by a drive device and to which ultrasonic energy is supplied from a ultrasound unit via at least one energy converter and a coupling element. A control unit is provided, which controls the ultrasound unit in such a way, that the frequency of the ultrasonic energy which is supplied to the blade via only one coupling element is keyed between at least a first and a second operating frequency or that the ultrasonic energy is supplied to the blade via a first coupling element with a first operating frequency and via a second coupling element with a second operating frequency, which frequencies are fixed or keyed between at least two operating frequencies.

Claims

1. A cutting device designed for cutting a process material with a drive device that is connected to a movable or rotatable blade, the cutting device comprising: an ultrasound unit that provides ultrasonic energy to an energy converter, the energy converter being connected to the movable or rotatable blade via a coupling element; and a control unit that controls the ultrasound unit such that the frequency of the ultrasonic energy is keyed between at least a first operating frequency and a second operating frequency, wherein keying between the first operating frequency and the second operating frequency is performed with a keying frequency in a range from 2 Hz to 500 Hz.

2. The cutting device according to claim 1, further comprising: at least one sensor that senses mechanical ultrasound waves that occur on the blade by the ultrasonic unit; a converter that converts signals provided by the at least one sensor and transfers the converted signal to a signal processing module provided in the control unit, wherein the signal processing module evaluates the converted signal and gathers corresponding measurement results; and a control module, of the control unit, that controls the ultrasound unit according to the gathered measurement results, in order to further optimize the measurement results.

3. The cutting device according to claim 1, further comprising: at least one temperature sensor that is connected to the control unit, and is mechanically coupled, directly or indirectly, with the blade, wherein the control unit is designed for observing the temperature of the blade or the temperature of the coupling element, and for controlling the ultrasound unit.

4. A cutting device for cutting a process material with a drive device that is connected to a movable or rotatable blade, the cutting device comprising: an ultrasound unit, wherein the ultrasound unit provides ultrasonic energy with a first operating frequency to a first energy converter, the first energy converter being connected to the movable or rotatable blade via a first coupling element, and the ultrasound unit provides ultrasonic energy with a second operating frequency to a second energy converter, the second energy converter being connected to the movable or rotatable blade via a second coupling element; and a control unit that controls the ultrasound unit such that the first operating frequency and the second operating frequency are keyed between at least two operating frequencies, wherein keying between the at least two operating frequencies is performed with a keying frequency in a range from 2 Hz to 500 Hz.

Description

(1) Below the invention is described with reference to drawings. Thereby show:

(2) FIG. 1 shows an inventive device for cutting a process material 8A, 8B, which is conveyed below and above a blade 11 that is held by a drive device 12 and that receives ultrasonic energy transferred via two ultrasound converters 13 from a ultrasound unit 4 which is further designed to receive ultrasound signals that are derived from the blade 11;

(3) FIG. 2 shows an inventive device for cutting a process material 8, comprising a cutting device 1 with four blades 11A, . . . , 11D, with which a process material 8, that is supplied in form of bars 8A, . . . , 8L to a conveyor table 93, is cut in slices 89;

(4) FIG. 3 shows the cutting device 1 of FIG. 2, with two drive units 12A, 12B with which the blades 11A, . . . , 11D can be moved upwards and downwards;

(5) FIG. 4a shows a blade 11 with a coupling element 15, on which a first energy converter 131 is arranged, which is supplied with ultrasonic energy, and on which a second energy converter 132 is arranged that seizes ultrasound waves occurring on the blade 11 and that converts these ultrasound waves into electrical signals that are evaluated by the control unit 6;

(6) FIG. 4b shows a spectrogram with an ultrasound pulse TP with oscillations of a plurality of frequencies f1, f2 and f3 that are applied to the blade 11 as well as the slope of the oscillations, which are then measured and evaluated;

(7) FIG. 5 shows the blade 11 of FIG. 4a with two coupling elements 15A, 15B that are connected to ultrasound converters 13A, 13B;

(8) FIG. 6 shows a multichannel ultrasound unit 4 and the control unit 6 in a preferred embodiment;

(9) FIG. 7a shows the blade 11 of FIG. 5 with the ultrasound converters 13A, 13B that are connected to the ultrasound unit 4, which receives and transmits ultrasound signals;

(10) FIG. 7b shows a frequency diagram with frequencies f1, 11a, f1b; f2, f2a, f2b, which are optimized by examining the oscillation behavior of the blade 11 or by means of the frequency response V of the blade 11;

(11) FIG. 7c shows standing waves sw1 that occur on the blade and that exhibit nodes swk and antinodes swb; and

(12) FIG. 8 shows an exemplary embodiment where the device 1 includes a movable or rotatable blade 11 that is held by a drive device 12.

(13) FIG. 1 shows a device 1 for cutting a process material 8A, 8B, which is supplied below and above a cutting tool or a blade 11 that is held by a drive device 12. It is shown that the drive device 12 holds the blade 11 on both sides with holding arms 121, which can synchronously be moved vertically downwards and upwards. The holding arms 121 can be connected with holding elements that are fastened to the blade 11. Preferably, the holding arms 121 can be moved with the coupling elements 15A, 15B, via which ultrasonic energy is coupled into the blade 11 (see FIG. 5).

(14) By means of the drive device 12 the blade 11 can be moved downwards and upwards, in order to cut in each direction of movement a first or a second portion of the supplied process material 8A, 8B respectively. For this purpose, the blade 11 comprises an upper cutting edge 101 and a lower cutting edge 102. In another exemplary embodiment, as shown in FIG. 8, by means of the drive device 12, the blade 11 can be rotated in a plane, which is perpendicular to the drive axis.

(15) For the implementation of the inventive method the cutting device 1 comprises a correspondingly designed control unit 6, a correspondingly designed ultrasound unit 4 and correspondingly designed ultrasound converters 13a, 13b. The ultrasound converters 13a, 13b are connected, preferably welded, by means of coupling elements 15A, 15B to the blade 11. In principle, every coupling or every embodiment of the coupling elements 15A, 15B can be used for the implementation of the inventive method.

(16) The ultrasound unit 4, which communicates with the control unit 6 and which is controlled by the control unit 6, comprises at least one transmission channel 41 and preferably at least one receiver channel 42. A transmission channel 41 comprises e.g. a fixed or variable oscillator, e.g. a voltage controlled oscillator VCO or a synthesizer. By means of the preferably controllable oscillators or synthesizers frequencies are selectively generated in the ultrasound range and are preferably supplied to a controllable output amplifier, as described below with reference to FIG. 6.

(17) A transmission channel 41 of the ultrasound unit 4 can be connected to a plurality of ultrasound converters 13A, 13B or energy converters 131 (see FIG. 6), which convert the electrical ultrasound oscillations into mechanical ultrasound oscillations that are applied via the coupling elements 15A, 15B to the blade 11. The ultrasound converters 13A, 13B can be supplied with identical ultrasound signals. Alternatively ultrasound signals with different frequencies can be supplied according to a time sharing method via switches to the ultrasound converters 13A, 13B. Further, for each ultrasound converter 13A or 13B a dedicated transmission channel 41 can be provided.

(18) By means of the control unit 6 the ultrasound unit 4 is controllable in such a way, that the frequency of the ultrasound waves, which are applied to the blade 11, can be keyed between at least a first and a second operating frequency f1a, f1b. On both ultrasound converters 13A, 13B the same frequencies can be present, which are keyed preferably within a few milliseconds. However preferably the ultrasonic energy is supplied to the blade 11 via a first coupling element with a first operating frequency f1 and via a second coupling element with a second operating frequency f2, which are fixed or switchable between at least two operating frequencies f1, f2 or f1a, f1b; f2a, f2b (see the frequency diagram in FIG. 7b). Preferably different frequencies are applied to the two ultrasound converters 13A, 13B, so that a frequency mixture results on the blade 11 and nodes do not appear or only for a short period of time.

(19) If only one coupling element is provided, then the frequencies f1, f2 or f1a, f1b; f2a, f2b are keyed according to a time sharing method. Alternatively two or more frequencies can be superimposed upon one another and can be coupled into the blade 11.

(20) FIG. 1 shows further that in a preferred embodiment ultrasonic energy can be decoupled from the blade 11 and can be transferred via one or a plurality of receiving channels 42 provided in the ultrasound unit 4 to the control unit 6. As described below, the ultrasound oscillations sensed on the blade 11 are evaluated, in order to determine the oscillation behavior of the blade 11 with the selected process parameters.

(21) FIG. 1 illustrates that preferably multiple measurements are executed during a cutting procedure. While the blade 11 traverses the process material 8A, signals sk1, . . . , sk5 are decoupled from the blade 11 in short intervals and are transferred via the receiver channel is 42 to the control unit 6. If optimal oscillation behavior of the blade 11 is detected, then the process parameters are not changed. However, if unfavorable oscillation behavior is detected, then the process parameters are changed in such a way, that the oscillation behavior is improved stepwise. Preferably, the process parameters are readjusted after every sampling of oscillations on the blade 11. Hence, while the blade 11 is guided through the process material 8, improvements and adaptions of the cutting processes can continuously be performed. Hence, the cutting process is not only in cases optimized, in which previous and following process material differ from one another. Corrections also apply for process material, which exhibits different properties across the cross-section or the cut surface.

(22) With optimization and adaption not only a continuously high cutting quality, but also a minimum strain on the cutting device is reached. On the one hand partial blockages when applying a cut are avoided. On the other hand energy losses and a corresponding heating of the blade 11 is avoided.

(23) Optimal oscillation behavior of the blade 11 appears in the range of the resonant frequency of the blade 11. Hence, as a starting point for the selection of the process parameters the resonant frequency of the blade 11 specified by the producer can be selected. Depending on the kind of process material 8 to be processed by the blade 11, the resonant frequency and therefore the oscillation behavior of the blade 11 will change, so that by means of the measurements of the signals sk1, . . . , sk5 illustrated in FIG. 1 a continuous optimization is pursued by determining the resonant frequency which currently occurs when processing a process material.

(24) Particularly the global maximum within the frequency response of the blade 11 is determined. Also local maxima that appear within the frequency response can advantageously be determined. Then preferably frequency keying between the determined maxima is performed. It is taken care that the operating frequencies f1a, f1b or f1, f2 are selected and keyed in such a way, that resulting nodes swk do not overlap.

(25) Operating frequencies are preferably selected in such a way, that the first and the second operating frequency f1a, f1b are set preferably in even frequency distance below and above the determined resonant frequency f1, or that a the first operating frequency f1a is set precisely at the resonant frequency f1 and the second operating frequency f1b is set in a range, in which only minimal damping occurs.

(26) When using only one resonant frequency or only one maximum, the distance between the first operating frequency that is set to resonance or to the maximum and the at least one second operating frequency preferably is kept as small as possible and as large as required, so that stationary wave nodes are avoided and the ultrasonic energy can act across the whole cutting edge of the blade onto the process material. In this case a frequency distance is selected for example in the range from 5 Hz to 500 HZ. Preferably an asymmetric switching is provided with a higher rest time in the range of the frequency, at which higher amplitudes occur.

(27) The distance between the operating frequencies f1a and f1b lies preferably in a range from 5 Hz to 10 kHz. Depending on the frequency response of the blade 11 smaller or larger frequency distances are selected.

(28) Keying of the first and the second operating frequency f1a, f1b or f1, f2 is done with a keying frequency lying preferably in a range from 2 Hz to 500 Hz. The keying is executed symmetrically or asymmetrically in time. E.g. during a longer first time interval the resonant frequency is applied to the blade 11, while for a shorter second time interval an operating frequency is applied to the blade 11 which deviates from the resonant frequency. In this case during the first time interval the blade 11 shall be applied with optimal effect on the process material 8 and during the second time interval a removal of obstacles shall be reached, which remain after the first time interval.

(29) As mentioned the inventive method can be used with different cutting devices or with further devices that comprise an ultrasound sonotrode.

(30) FIG. 2 shows a cutting device 1 with four cutting tools 11A, . . . , 11D, a pushing unit 95 with a pushing tool 94, two drive units 12A, 12B for driving the cutting tools 11A, . . . , 11D, and a conveyor table 93 on which the process material 8 is placed and pushed by means of the pushing tool 94 towards the cutting tools 11A, . . . , 11D. The cutting device 1 is held by a mounting structure 5.

(31) The process material 8 consists of twelve cylindrical or bar-shaped units 8A, . . . , 8L that are guided in parallel towards the four cutting tools 11A, . . . , 11D, so that always three of the units of process material 8A, . . . , 8L are simultaneously cut by one of the cutting tools 11A; . . . ; 11D. At the front side the units of process material 8A, . . . , 8L, which are delivered in parallel, are held by a downholder in a desired position, while the cut is executed.

(32) The cutting unit 1 comprises the four cutting tools 11A; . . . ; 11D, which are connected each to an ultrasound converter 13 and which can be vertically lowered and lifted again by the drive units 12A, 12B in order to cut slices 89 from the units of process material 8. The slices 89 fall onto a conveyor belt 92 of a receiving conveyor 9, which comprises a drive motor 91.

(33) Further provided is a control unit 6 that controls the cutting device 1, the conveyor devices and the ultrasound unit 4. The control unit 6 is connected via a first control line 61 to the drive units 12A, 12B, a second control line 62 to the conveyor devices, a third control line 63 to the ultrasound unit 4 and a fourth control line 69 to the receiving conveyor 9. Via a keyboard and measurement devices 71, 72, such as transducers and sensors, information is supplied to the control device 6, with which the cutting process and the conveyor process can be controlled.

(34) FIG. 3 shows the dismounted cutting device 1 of FIG. 1, which comprises two to identical cutting modules, which are held by a mounting plate that is part of a mounting structure 5 of the device. Each of the cutting modules comprises a drive unit 12A; 12B and a bearing structure 128A; 128B that is connected to the mounting structure 5 and that allows vertically lifting and lowering a related first or second bearing block 129A, 129B. Each bearing block 129A; 129B is equipped with two ultrasound converters 13A, 13B or 13C, 13D respectively, which are connected each via a coupling element 15 to a cutting tool 11A, 11B, 11C or 11D.

(35) The cutting tools 11A, . . . , 11D comprise each a blade 11 with a blade back on which the curved coupling elements 15 are welded, whereby ultrasonic energy can be coupled into the blades 11.

(36) FIG. 4a shows that the coupling element 15 is connected, e.g. screwed to a beam 130, on which a first energy converter 131 is placed that is supplied with ultrasonic energy, and on which a second energy converter 132 is placed, that senses ultrasound waves appearing on the blade 11 and that converts these ultrasound waves into electrical signals, which are forwarded to the control unit 6. The beam 130, which together with the energy converters 131, 132 forms an ultrasound converter 13, comprises e.g. on the front side the screw, which is turned into a threaded bore that is provided in the coupling element 15. The ultrasound unit 4 comprise a plurality of transmission channels 41 and a plurality of receiver channels 42, so that a plurality of ultrasound converters 13 can be served.

(37) The energy converters 131, 132 comprise preferably each a piezo element, which is enclosed between two electrodes, e.g. metal plates, of which one is seated on the beam 130 and the other is connected to an electrical line 401, 402. The transmission channel 41 of the ultrasound unit 4 provides electrical ultrasound signals via the connecting line 401 to the first energy converter 131. The second energy converter 132 or the sensor 71 senses mechanical ultrasound waves from the blade 11 and converts these mechanical waves into electrical ultrasound waves, which are forwarded via the second connecting line 402 to a receiver channel 42 of the ultrasound unit 4. The received ultrasound waves are amplified if required, filtered, converted and 4 forwarded to an evaluation module 600 in the control unit 6. The evaluation module 600 determines the current oscillation behavior of the blade 11 and compares it with specified values, whereafter correction measures are determined. E.g. it is determined, that at least one of the operating frequencies is shifted, or that the signal amplitude of at least one of the operating frequencies is increased or reduced. Corresponding information is forwarded from the evaluation module 600 to a control module 60, which determines the operating frequencies, the keying frequencies, the keying intervals and the signal amplitude and provides corresponding control signals. For controlling the evaluation module 600 and the control module 60 and operating program is provided, which controls the program sequence and communicates via interfaces with the user and external computers or electronic units.

(38) Process optimization can be done in several ways. As mentioned the oscillation behavior of the sonotrode or the blade 11 is continuously observed and optimized. The control unit 6 can also automatically optimize the process parameters. For this purpose, the control unit 6 applies test signals TP to the blade 11 during the operation process or during test phases and evaluates echo signals f1, f2, f3. Evaluation of the test signals and the operating signals or operating frequencies, which are gathered during the process sequence, can be done in the same way.

(39) FIG. 4b shows exemplarily a spectrogram with an ultrasound pulse TP, which comprises oscillations with a plurality of frequencies f1, f2 and f3. After the ultrasound pulse TP has been applied to the blade 11, the oscillation behavior of the blade 11 or the further sequence of the oscillations f1, f2 and f3 is examined. It is examined with which amplitudes the individual oscillations f1, f2 and f3 occur and how fast they decay. The curves df1, df2 and df3 show the slope of the decay of the oscillations f1, f2 and f3. After the evaluation module 600 has determined the frequencies, at which maximum oscillation amplitude and a minimum damping occur, the related information is forwarded to the control module 60.

(40) If the frequency f2 is the operating frequency, then the test pulse TP is additionally provided with two frequencies f1, f3 for example, which are set below and above the operating frequency f2. By evaluating the echo signals of the three frequencies f1, f2, and f3 it can then be determined, that at frequency f1 a higher amplitude and a lower damping results. Hence, the evaluation module 600 will provide this information to the control module 60, whereafter with frequency f1 as new operating frequency an improved oscillation behavior of the blade 11 can be reached. The control module 60 can immediately take over frequency f1 as new operating frequency or include this information in the further evaluation process. Preferably, parameters are also taken into consideration for the evaluation, which relate to properties or expected changes of the process material 8.

(41) FIG. 5 shows blade 11 of FIG. 4a with two coupling elements 15A, 15B that are connected to ultrasound converters 13A, 13B. In principle, ultrasound converters 13A, 13B can fully or partly incorporate ultrasound units 4. It is shown that blade 11 is held by the coupling elements 15A, 15B that are welded to the blade 11. The coupling elements 15A, 15B themselves are held by symbolically drafted holding arms 121, as has been described with reference to FIG. 1.

(42) FIG. 6 shows exemplarily the multichannel ultrasound unit 4, which is connected via a bus system 63 to the control unit 6 for exchanging data. The ultrasound unit 4 comprises two transmission channels 41 and two receiver channels 42.

(43) Each transmission channel 41 comprises a D/A converter 411 that converts the digital commands of the control unit 6 into analogue control signals that are forwarded to the controllable oscillators 412. Instead, also a synthesizer can be used, which is directly controllable by the control unit 6 and which can simultaneously provide a plurality of operating frequencies. The oscillations delivered by the controllable oscillators 412 are forwarded each to a controllable amplifier 413, which delivers the oscillations with selectable amplitude to the energy converter 131. The control of the amplifier 413 is again performed by the control unit 6 or the control module 60. Hence, a plurality of ultrasound signals with selected frequency and selected amplitude can simultaneously be provided to the related energy converter 131 or ultrasound converter 13.

(44) Each receiver channel 42 comprises preferably an input amplifier 421, preferably a filter stage 422 connected thereto that only lets pass frequencies of interest, as well as an A/D converter, which converts the analogue signals into digital data. The digital data are forwarded to the evaluation module 600, which comprises a signal processor for example and which is preferably suited to perform a Fourier-transformation.

(45) FIG. 7a shows the blade 11 of FIG. 5 with the ultrasound converters 13A, 13B that are connected via connecting systems 40A, 40B to an ultrasound unit 4 that provides and receives ultrasound signals, as has been described above with reference to FIGS. 4a, 4b and 6.

(46) It is shown, that the cutting device 1 is currently in operation and that two standing waves sw1, sw2 occur at the cutting edge of blade 11, which are superimposed upon one another, so that wave nodes swk of the one standing wave sw1 are located within the antinodes swb of the other standing wave sw2. The two waves sw1, sw2 can be superimposed upon one another or can be switched on alternatingly, so that always within a few milliseconds, optionally within fractions of a millisecond, each zone of the process material to be cut is exposed to the maximum intensity of the ultrasonic energy and an optimal cutting line is guaranteed. FIG. 7c illustrates the first standing wave sw1 with wave nodes swk and antinodes swb.

(47) FIG. 7a further shows temperature sensors 72, 73, preferably infrared sensors, with which the temperature of the blade 11 or the coupling elements 15A, 15B, particularly the connecting points, can be observed. If a critical temperature rise is detected, then the power applied to the blade 11 can be reduced. Further, an examination procedure can be executed in order to detect inadequate process parameters. E.g. the frequency response of the blade 11 is recorded, in order to detect shifts of the resonant frequencies. In this way damage to the blade 11 can be avoided in good time.

(48) FIG. 7b shows a frequency diagram with frequencies f1, f1a, f1b, f2, f2a, f2b, that are selectable by the control module 60. For determining the operating frequencies preferably the frequency response V of the blade 11 is recorded, which is shown in FIG. 7b as an example. It can be seen that the frequency response V exhibits four maxima that lie above a predetermined threshold s.

(49) The maxima M1, . . . , M4 lie at locations at which ultrasonic energy can optimally enter the blade 11 and can cause oscillations in the blade 11. E.g. by piezo electrical elements, the mechanical oscillations are converted into electrical signals, whose voltage characteristic or amplitudes are shown in FIG. 7b.

(50) Frequencies of the maxima located above this threshold s are suitable operating frequencies. M3 is the global maximum, while M1, M2 and M4 are local maxima. Now, the operating frequencies are selected in such a way that the wave nodes and the antinodes of the resulting standing waves overlap. In the present example, the operating frequencies f1 and f2 at the locations of the global maxima M3 and the local maxima M2 have been selected. Alternatively, further combinations of the frequencies of said maxima, e.g. M3 and M4 or M1, M2 and M4, or M1 and M4, can be selected. Alternatively a resonant frequency f1 is determined, whereafter on both sides of this resonant frequency f1 operating frequencies f1a, f1b are determined, which are forwarded to only one or both ultrasound converters 13A, 13B. It is shown that the maxima shift e.g. due to changes of the consistency of the process material 8 wherefore the operating frequencies f1, f2 or f1a, f1b are updated accordingly and consistently optimized according to the inventive method.

(51) Preferably a plurality of recipes is provided, with which specific process parameters for a blade 11 and preferably a specific process material 8 are determined. Process parameters are for example the operating frequencies, the oscillation amplitudes preferably for each of the operating frequencies, the keying frequency, the minimum and maximum power, as well as the maximum temperature of the blade 11. Thereby, recipes can be selected and set permanently or sequentially or randomly. By measuring the oscillation behavior of the blade 11 for each recipe, optimal recipes can immediately be selected and applied. Hence, in preferred embodiments not only an individual process parameter, but a group of process parameters, optionally a whole recipe, is switched over.

(52) Preferably the recipes are consistently optimized by means of the inventive measurement process and stored again. Hence, if changes of the process material 8 occur, suitable recipes can immediately be downloaded.

REFERENCES

(53) [1] DE102005006506A1 [2] EP2551077A1 [3] DE102009045945A1