Abstract
A device for ground compaction, comprising a frame and a drive motor supported by the frame, a vibration exciter driven by the drive motor and a ground compaction apparatus, in particular a base plate or a roller drum, that is connected to the vibration exciter, wherein the vibration exciter causes the ground compaction apparatus to vibrate at a fixed vibration frequency or within a vibration frequency range during a compaction operation, and wherein a conversion device for the conversion of vibrations into electric energy is provided which converts vibrations of the device for ground compaction into electric energy, wherein the conversion device comprises two spring-mass systems with different resonance frequencies, and wherein a control unit is provided which determines the degree of compaction of the ground from the electric energy obtained by the individual spring-mass systems, in particular the respective voltages. Moreover, the invention relates to a method for monitoring changes in the ground compaction produced with a device for ground compaction.
Claims
1. A device for ground compaction, comprising: a frame and a drive motor supported by the frame; a vibration exciter driven by the drive motor; and a ground compaction apparatus, comprising a base plate or a roller drum, which is connected to the vibration exciter, wherein the vibration exciter causes the ground compaction apparatus to vibrate at a fixed vibration frequency or within a vibration frequency range during a compaction operation, and wherein a conversion device for the conversion of vibrations into electric energy is provided which converts vibrations of the device for ground compaction into electric energy, wherein the conversion device comprises at least two spring-mass systems with different resonance frequencies, and wherein a control unit is provided which ascertains the degree of compaction of the ground from the electric energy obtained by the individual spring-mass systems.
2. The device for ground compaction according to claim 1, wherein the ratio of the resonance frequencies of the at least two spring-mass systems is from 1:1.5 to 1:3.
3. The device for ground compaction according to claim 1, wherein the two spring-mass systems are configured in such a way that the resonance frequency of one spring-mass system is above the set vibration frequency or above the mean value of the vibration frequency range and/or the resonance frequency of the other spring-mass system is below the vibration frequency or below the mean value of the vibration range.
4. The device for ground compaction according to claim 1, wherein the two spring-mass systems are configured in such a way that the resonance frequency of one spring-mass system is twice the vibration frequency or twice the mean value of the vibration frequency range and/or the resonance frequency of the other spring-mass system is half the vibration frequency or half the mean value of the vibration frequency range.
5. The device for ground compaction according to claim 1, wherein the conversion device comprises three spring-mass systems which are configured in such a way that the resonance frequency f.sub.1 of the first spring-mass system corresponds to the vibration frequency or the mean value of the vibration frequency range, the resonance frequency f.sub.2 of the second spring-mass system is twice the vibration frequency or twice the mean value of the vibration frequency range, and the resonance frequency f.sub.0 of the third spring-mass system is half the vibration frequency or half the mean value of the vibration frequency range.
6. The device for ground compaction according to claim 1, wherein the conversion device is arranged on a ground-compacting component in direct contact with the ground.
7. The device for ground compaction according to claim 1, wherein the conversion device comprises at least one of the following features: the conversion device is part of an assembly unit together with a consumer, the control unit and/or a transmitting unit and/or a display device; the conversion device comprises at least one voice coil; the conversion device comprises a permanent magnet, consisting of neodymium; the conversion device is arranged on the device for ground compaction in such a manner that it is positioned either centrally or in an edge region in relation to a ground contact surface.
8. The device for ground compaction according to claim 1, wherein the conversion device comprises at least one linear generator.
9. The device for ground compaction according to claim 1, wherein the conversion device supplies a consumer with electric energy.
10. The device for ground compaction according to claim 1, wherein the device for ground compaction is an attachable compactor, a vibratory plate compactor or a vibrating roller.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will be explained in greater detail below with the help of the examples shown in the figures, which show schematically:
(2) FIG. 1A is a side view of an attachable compactor;
(3) FIG. 1B is a side view of a compaction roller;
(4) FIG. 1C is a side view of a vibrating tamper;
(5) FIG. 1D is a side view of a vibrating plate;
(6) FIG. 2 is an assembly unit with a conversion device;
(7) FIG. 3 is a frequency-amplitude diagram of the vibration of the spring-mass systems in the case of soft ground;
(8) FIG. 4 is a frequency-amplitude diagram of the vibration of the spring-mass systems in the case of firmer ground;
(9) FIG. 5 is a frequency-amplitude diagram of the vibration of the spring-mass systems in the case of extremely firm ground; and
(10) FIG. 6 is a flow chart of the method for monitoring changes in the ground compaction produced with a device for ground compaction.
DETAILED DESCRIPTION
(11) Similar parts or parts with a similar function are designated with identical reference numbers in the figures. Recurring components are not necessarily designated separately in each figure.
(12) FIGS. 1A, 1B, 1C and 1D respectively show generic devices for ground compaction 1. Specifically, FIG. 1A shows an attachable compactor, FIG. 1B shows a compaction roller,
(13) FIG. 1C shows a vibrating tamper, and FIG. 1D shows a vibrating plate. All devices for ground compaction 1 include a machine frame or frame 2. Moreover, they comprise a drive motor 3, which, e.g. in the cases of the compaction roller of FIG. 1B, the vibrating tamper of FIG. 1C and the vibrating plate of FIG. 1D, is a combustion engine, in particular a diesel combustion engine. In the case of the attachable compactor of FIG. 1A, the drive motor 3 is a hydraulic motor, which can be connected to and driven by the hydraulic system of an excavator, e.g., by means of a quick-coupling system. Among other things, the drive motor 3 drives a vibration exciter 4, which causes the ground compaction apparatus of the device for ground compaction 1 to vibrate. The ground compaction apparatus is configured as a base plate 5 in the attachable compactor of FIG. 1A, the vibrating tamper of FIG. 1C and the vibrating plate of FIG. 1D, and as a roller drum 6 in the compaction roller of FIG. 1B. During a compaction operation, the device for ground compaction 1 is guided with the base plate 5 or the roller drum 6 over the ground to be compacted. As a result of the weight of the device 1 and the vibrating motion of the ground compaction apparatus, the ground driven over by the device 1 is increasingly compacted. In addition, the devices for ground compaction 1 comprise a conversion device 7. In principle, the conversion device 7 can be arranged anywhere on the devices 1 and is specifically arranged, e.g., on the base plate 5 in the attachable compactor of FIG. 1A and the vibrating plate of FIG. 1D. In the vibrating tamper of FIG. 1C, the conversion device is illustratively fastened to the tamper foot, but it can also be arranged at other locations on the device 1 such as, e.g., on the base plate 5. In the compaction roller of FIG. 1B, conversion devices are respectively arranged on the two roller drums 6, the conversion device be arranged for the sake of illustration on the inner circumference of the inner shell of the hollow-cylindrical roller drum of one of the roller drums 6 and on the drum mount of the other roller drum 6. However, as mentioned, these arrangement positions of the conversion device 7 are merely for the sake of illustration.
(14) FIG. 2 shows the structure of a conversion device 7 as implemented in the device for ground compaction 1 of FIGS. 1A to 1D. In total, the conversion device 7 comprises two linear generators 16, configured here as a first spring-mass system 10 and a second spring-mass system 11. An optional, third spring-mass system 8, which can also be arranged in and comprised by the conversion device 7, is further suggested by means of dashed lines. Each spring-mass system 10, 11, 8 comprises at least onein the shown example shown in fact twospring(s) 13. The pretensioned springs 13 support a permanent magnet 15 and are movable, in particular linearly movable. A coil 14 made of an electrically conductive material, e.g. copper wire, is arranged around the permanent magnet 15 so that movement of the permanent magnet 15 inside the coil 14 induces an electric current in the coil 14. By virtue of the spring-mounted permanent magnets 15, the conversion device 7 is configured to be vibration-sensitive. This means that the conversion device 7, when vibrated, obtains electric energy in the linear generators 16. In the embodiment shown, the conversion device 7 then supplies a control unit 17 and a transmitting unit 9 with the obtained electric energy. For example, the control unit 17 measures the electric energy produced by the respective spring-mass systems 10, 11, 8 and passes the obtained data on to the transmitting unit 9 as either raw or processed data. The transmitting unit 9 transmits the data via a wireless connection to a receiving device (not shown). Any type of radio transmission is an option in this connection, e.g. WLAN, Bluetooth, an infrared interface and the like. The conversion device 7 is configured together with the control device 17 and the transmitting unit 9 as an assembly unit 12. The assembly unit 12 is a single, prefabricated component, which is designed in such a way that it can be installed as a whole in a modular fashion on a device for ground compaction 1 in a single installation step. The assembly unit 12 can also be installed in an already existing device for ground compaction 1 and is thus also suitable for retrofitting.
(15) FIGS. 3, 4 and 5 respectively show a frequency-amplitude diagram in which the frequency f is plotted on the abscissa and the amplitude A is plotted on the ordinate. The frequency f.sub.1 is the vibration frequency or mean value of the vibration frequency range set by the vibration exciter 4. The frequency f.sub.2 is twice the frequency of f.sub.1, while the frequency f.sub.0 is half the frequency of f.sub.1. The frequency f.sub.2 is thus the higher harmonic while f.sub.0 is the lower harmonic of the vibration frequency f.sub.1. The graphs respectively plotted in FIGS. 3 to 5 show the progression of the amplitudes of the spring-mass systems 10, 11, 8 as a function of the frequency f. In the embodiment shown, the graph with the solid line relates to the first spring-mass system 10, which has a resonance frequency f.sub.1 matching the vibration frequency f.sub.1 set by the vibration exciter 4; the dashed graph relates to the second spring-mass system 11, which has a resonance frequency f.sub.2 twice as large as the vibration frequency f.sub.1 set by the vibration exciter 4; and the dotted graph relates to the third spring-mass system 8, which has a resonance frequency f.sub.0 half as large as the vibration frequency f.sub.1 set by the vibration exciter 4. Excitation of the conversion device 7 and thus of the spring-mass systems 10, 11, 8 at the resonance frequencies f.sub.0, f.sub.1 or f.sub.2, results in a significant increase of the amplitude A for the respective resonance frequencies f.sub.0, f.sub.1 or f.sub.2 at the corresponding spring-mass systems 10, 11, 8. With a larger amplitude A, the permanent magnet is moved through the coil 14 faster and farther so that more electric energy is generated in the coil 14, e.g. a higher voltage results. Since the consumers, e.g. the control unit 17 and the transmitting unit 9 or a display device (not shown), always need to be supplied with sufficient electric energy, it is important that the total amount of electric energy provided by all linear generators 16 is sufficient to supply the consumers.
(16) FIG. 3 shows the operation of the device for ground compaction on a very soft substrate. The picture essentially corresponds to a situation in which the ground compaction apparatus is vibrating freely in the air. The vibration of the ground compaction apparatus essentially corresponds to a vibration at the vibration frequency f.sub.1, i.e. the frequency set by the vibration exciter 4. Since this frequency f.sub.1 also corresponds to the resonance frequency of the first spring-mass system 10, the first spring-mass system 10 vibrates accordingly with a high amplitude, as illustrated in the figure. In contrast, the other two spring-mass systems 11, 8 practically do not vibrate at all, which is suggested by the horizontal dashed and dotted lines at the respective resonance frequencies f.sub.2 and f.sub.0, respectively. FIG. 4 shows the operation of the device for ground compaction on a substrate that is clearly firmer than that of FIG. 3. This can be due to the fact that, for example, the ground has already been compacted to a certain degree. Due to the more solid substrate, the vibration response of the ground has changed so that the vibration of the ground compaction apparatus no longer comprises solely the vibration frequency f.sub.1 set by the vibration exciter 4. In addition to the vibration frequency f.sub.1, the vibration of the ground compaction apparatus here further comprises a component with twice the frequency f.sub.2, the so-called higher harmonic. Since the conversion device 7 comprises a second spring-mass system 11 with a resonance frequency f.sub.2 set at the higher harmonic, the second spring-mass system 11 now also starts to vibrate appreciably in this phase and thus produce electric energy. A further increase in ground stiffness or further increase in the degree of compaction of the substrate then finally results in the situation depicted in FIG. 5. FIG. 5 shows an operational phase in which the substrate has already been compacted so tightly that the ground compaction apparatus starts to jump and partially lose contact with the ground. As a result, a new vibration component with the frequency f.sub.0 is created in the vibration of the ground compaction apparatus, which is half as large as the vibration frequency f.sub.1 set by the vibration exciter 4. Consequently, the third spring-mass system 8 with a resonance frequency set at the lower harmonic with the frequency f.sub.0 also starts to vibrate appreciably and produce electric energy. The electric energy respectively produced at the individual spring-mass systems 10, 11, 8 is registered by the control unit 17. As is evident in particular from a comparison of FIGS. 3, 4 and 5, an increasing ground stiffness causes the individual spring-mass systems 10, 11, 8 to deliver different signals, in particular in relation to one another, which allow an inference regarding the ground stiffness or degree of compaction of the ground. Provision can now be made, for example, for the control unit 17 to convert the signals received from the spring-mass systems 10, 11, 8 directly into an indication of the ground stiffness. Alternatively, the control unit 17 can be configured to simply relay the unprocessed measured values so that the determination of the ground stiffness or degree of compaction occurs later. The data are relayed, for example, to the transmitting unit 9, which transmits them to a receiving device via a wireless connection. The receiving device then, for example, ensures that the data are processed further and/or that an indication of the ground stiffness is displayed to the operator of the device for ground compaction. This indication, however, can also occur directly at the assembly unit 12, e.g., by means of a display which is attached to the assembly unit 12 and which is visible to an operator from the outside. The determination of the ground stiffness occurs here in such a manner that an increase in the production of electric energy by the spring-mass system 11 with a resonance frequency f.sub.2 corresponding to twice the vibration frequency f.sub.1, in particular in comparison with the power generation of the spring-mass system 10 with a resonance frequency corresponding to the vibration frequency f.sub.1 set by the vibration exciter 4, is translated into a corresponding increase in ground stiffness. An increase in the production of electric energy by the spring-mass system 8 with a resonance frequency f.sub.0 set at half the vibration frequency f.sub.1 is likewise translated into an even larger increase in ground stiffness. This way, the ground stiffness can be ascertained based solely on the production of electric energy by the individual spring-mass systems 10, 11, 8 so that a conventional accelerometer for measuring the stiffness of the ground is not necessary.
(17) The vibration frequencies set by different devices for ground compaction 1 or their vibration exciters 4 vary depending on the type of device for ground compaction 1 in question as well as on the model and configuration. For example, the vibration frequencies usually range from 35 to 60 Hz for attachable compactors, from 35 to 100 Hz for vibratory plate compactors, from 25 to 75 Hz for rollers, and from 10 to 14 Hz for tampers. In the case of an attachable compactor with a working frequency of, e.g., 45 Hz, a spring-mass system would have to be adjusted to f.sub.1=45 Hz. Accordingly, a further spring-mass system would then have to be adjusted to f.sub.2=90 Hz, i.e. twice the working frequency. A further spring-mass system could then also be adjusted to, e.g., the lower harmonic at f.sub.0=22.5 Hz. For the determination of the stiffness of the ground, the ratio of the amplitude of the higher harmonic (90 Hz) to the amplitude of the base frequency (45 Hz) could then be determined. This ratio increases with increasing compaction. It is also possible for the attachable compactor to have two working frequencies, e.g. 45 Hz and 60 Hz. In this case, as a compromise, the resonance frequency of one spring-mass system could be set to f.sub.1=52.5 Hz and the resonance frequency of a further spring-mass system to f.sub.2=105 Hz. This configuration would provide sufficient excitation of the spring-mass systems at both working frequencies 45 Hz and 60 Hz so that a useable signal can be generated. The examples given for the attachable compactor can be applied to the other devices for ground compaction 1 by adapting the standard vibration frequencies of these devices 1. It is important here to select the resonance frequencies of the spring-mass systems in such a way that a sufficiently high amplification of at least 2 is ensured at the corresponding operating frequencies. This minimum requirement applies to all embodiments of the present invention.
(18) FIG. 6 shows a flow chart of the method 19 according to the invention for monitoring changes in the ground compaction produced with a device for ground compaction 1. The method 19 starts with compacting 20 a ground with the aid of a ground compaction apparatus vibrated by means of a vibration exciter 4. Generating 21 electric energy with the aid of the conversion device 7 occurs at the same time, as explained above. This occurs in particular by means of at least two spring-mass systems 10, 11, 8 with different resonance frequencies f.sub.0, f.sub.1, f.sub.2. According to the method 19, a determining and monitoring 23 of the electric energy generated by each individual spring-mass system 10, 11, 8 or a corresponding parameter then occurs before a correlating 24 of the determined electric energy generated or the corresponding parameter with the change in ground compaction, also as described above. In this manner, it is not necessary to provide a separate accelerometer for ascertaining the ground stiffness, which reduces the total cost of the device for ground compaction 1.
