MONITORING DEVICE FOR A SLIPFORM PAVER FOR MONITORING THE COMPACTION OF CONCRETE AND METHOD FOR MONITORING THE COMPACTION OF CONCRETE DURING THE OPERATION OF A SLIPFORM PAVER

Abstract

A monitoring system is provided for a slipform paver for monitoring the compaction of concrete placed in a slipform with at least one concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance. In addition, a method is provided for monitoring the compaction of concrete placed in a slipform of a slipform paver with at least one concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance. The monitoring system and the method are characterized in that the pressure in the hydraulic fluid system is measured by at least one pressure sensor arranged in the hydraulic fluid system, which pressure sensor generates a pressure signal correlating with the pressure in the hydraulic fluid, and the compaction of the concrete placed in the slipform is concluded on the basis of an analysis of the pressure signal.

Description

The present application claims priority to German Patent Application Ser. No. DE 10 2023 123 252.5 filed Aug. 29, 2023, which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The disclosure relates to a monitoring device for a slipform paver for monitoring the compaction of concrete placed in a slipform of a slipform paver by at least one concrete compaction device, wherein the concrete compaction device has a hydraulic motor for driving a vibration-generating imbalance. In addition, the disclosure relates to a method for monitoring the compaction of concrete placed in a slipform of a slipform paver with at least one concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance.

Description of the Prior Art

Known slipform pavers are equipped with a slipform, also known as a concrete mold. A slipform paver is described, for example, in EP 1 103 659 B1 (U.S. Pat. No. 6,481,924). With slipforming, structures of different shapes, such as safety barriers, curbs or entire concrete roadways, can be produced. The concrete is continuously poured into the slipform, which moves over the substrate at a constant velocity. There must always be a certain amount of concrete in the slipform so that sufficient pressure is exerted on the concrete by its own weight. The concrete must be compacted in and/or in front of the slipform. Concrete compaction devices are used to compact the concrete, which are provided on or in the slipform. These concrete compaction devices are also known as external or internal vibrators. Slipform pavers are often equipped with several bottle-shaped or bar-shaped internal vibrators, which are suspended in and/or in front of the slipform and are immersed in the concrete during operation.

When operating a slipform paver, the problem arises that technical defects in the concrete vibrators can lead to the concrete in the slipform not being sufficiently compacted. Particularly when operating internal vibrators that are fully immersed in the concrete, technical defects in the individual vibrators can be difficult for the slipform paver operator to recognize. Since subsequent compaction is not possible, components can be produced with which the concrete does not meet the requirements in places. Due to their lack of strength, these concrete components have to be demolished and rebuilt, which involves enormous costs.

Electric concrete vibrators are known that have an asynchronous motor that drives an eccentric flywheel mass (imbalance) that causes the concrete vibrator to vibrate. The compaction performance of the vibrator depends on the frequency of the vibrations, which in turn is determined by the rotational speed of the asynchronous motor.

DE 10 2019 125 590 A1 (U.S. Pat. No. 11,525,224) describes a monitoring device for monitoring the compaction of concrete, which is intended for a slipform paver whose at least one concrete compaction device has an asynchronous motor for driving the vibration-generating eccentric flywheel mass (imbalance). The functional principle of the known monitoring device is based on the realization that during operation of a concrete compaction device with which the eccentric flywheel mass (imbalance) is driven by an asynchronous motor, the rotor shaft can deform elastically due to the imbalance during operation of the asynchronous motor. If the rotor shaft bends, the width of the air gap between the stator and rotor changes, which can be detected in the amplitude spectrum of the stator current. With the known monitoring device, the monitoring of the compaction of the concrete is based on the evaluation of the stator current of the asynchronous motor, in order to be able to conclude a change in the compaction of the concrete placed in the slipform of the slipform paver.

In addition to electric concrete vibrators, hydraulic concrete vibrators are also known, which have a hydraulic motor to drive the eccentric flywheel mass (imbalance). The monitoring device known from DE 10 2019 125 590 A1 (U.S. Pat. No. 11,525,224) is neither intended nor suitable for such concrete vibrators due to the different operating principles of the drives of the eccentric flywheel mass.

In general, the upper and lower operating limits of a hydraulic concrete vibrator can be set between 8000 and 12000 rpm, for example. When using hydraulic vibrators, the problem arises in practice that the vibrator must be operated at a predetermined rotational speed, for example at a rotational speed of 10,500 rpm, in order to achieve the desired compaction of the concrete. However, the actual rotational speed of the hydraulic motor never reaches the nominal rotational speed resulting from the nominal volume flow and nominal pressure due to volumetric losses (leakage oil), and the achievable rotational speed of a hydraulic vibrator decreases with increasing wear due to these losses (leakage oil). However, prior to concreting, the wear condition and thus the achievable rotational speed are not known in practice. Therefore, it cannot be guaranteed that the rotational speed required for compaction is achieved.

U.S. Pat. No. 6,055,486 A describes a hydraulically driven internal vibrator with rotational speed control. For recognizing the operating status of the hydraulic vibrator, a device is proposed with which the vibrations of the vibrator are recorded. Acceleration sensors are proposed for recording the vibrations, which are to be provided in the vibrator. However, the disadvantage is that the acceleration sensors are exposed to harsh environmental conditions. Such sensors, which are installed in hydraulic concrete vibrators, are not only exposed to vibrations, but also to extremely high temperatures of over 100° C. In addition, the arrangement of a sensor within the vibrator is in principle very difficult due to the limited installation space. Furthermore, supply lines for the power supply of the sensors and signal lines for the recorded signals must be routed over long distances to and from the vibrators immersed in the concrete, which signifies considerable effort and makes the whole system highly susceptible to faults.

SUMMARY OF THE DISCLOSURE

The disclosure is based on the object of creating a monitoring system for a slipform paver with at least one concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance, which enables reliable monitoring of the compaction of the concrete placed in the slipform during operation of the slipform paver under the harsh environmental conditions. A further object of the disclosure is to provide a method that permits reliable monitoring of the compaction of the concrete placed in the slipform with a concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance. One object of the disclosure is also to provide a slipform paver with such a monitoring system. The disclosure is also based on the object of enabling the use of conventional hydraulic concrete vibrators that are not equipped with sensors for monitoring the operating status or do not need to be equipped with such sensors.

These objects are achieved according to the disclosure with the features of the independent claims. The dependent claims relate to advantageous embodiments of the disclosure.

The monitoring system according to the disclosure and the method according to the disclosure are based on the following knowledge gained from tests. A hydraulically driven concrete compaction device generates an oscillation at the rotational frequency of the hydraulic motor due to the imbalance. This oscillation is transmitted to the hydraulic fluid (hydraulic oil) for driving the hydraulic motor, which flows through the hydraulic motor and the connecting lines of the concrete vibrator. The change in velocity caused by the oscillation results in a change in the local acceleration, which in unsteady flows causes the occurrence of additional inertial forces that lead to a corresponding change in pressure. These pressure fluctuations in the hydraulic fluid and the resulting changes in density propagate at the speed of sound as longitudinal waves in the fluid and can be recorded with a suitable sensor system.

The monitoring system according to the disclosure and the method according to the disclosure are characterized in that the pressure in the hydraulic fluid is measured at at least one point of the hydraulic fluid system using at least one pressure sensor arranged in the hydraulic fluid system, which pressure sensor generates a pressure signal correlating with the pressure in the hydraulic fluid, and the compaction of the concrete placed in the slipform of the slipform paver with the at least one concrete compaction device is concluded on the basis of an analysis of the pressure signal. Consequently, it can be determined whether the compaction of the concrete with the at least one concrete compaction device is sufficient. In addition, it can be determined whether the concrete compaction device is being operated with sufficient power (imbalance). Furthermore, it can be determined whether the hydraulic motor of the concrete compaction device is being operated at a sufficient rotational speed. This would not be the case if the rotational speed of the hydraulic motor was not within predetermined limit values or did not correspond to a predetermined rotational speed.

The monitoring system according to the disclosure has an evaluation device or controller for evaluating (analyzing) the pressure signal of the at least one pressure sensor, which is configured in such a way that the compaction of the concrete is concluded on the basis of an analysis of the pressure signal. The controller is preferably configured in such a way that the amplitude spectrum of the pressure signal is ascertained for analyzing or evaluating the pressure signal.

The monitoring system according to the disclosure and the method according to the disclosure have the decisive advantage that the monitoring of the compaction of the concrete is not carried out with components, in particular sensitive sensors, in the vicinity of the concrete compaction device, which would be exposed to the harsh environmental conditions during the operation of the slipform paver. Therefore, there is no risk of such components failing, as a result of which monitoring would be unreliable. Suitable sensors for recording the pressure fluctuations can be provided in a non-critical environment outside the concrete compaction device. Furthermore, longer supply lines, which would signify considerable expense and make the whole system highly susceptible to faults, can also be omitted.

The controller is preferably a digital signal processing device, which is configured in such a way that the pressure signal is sampled, wherein the amplitude spectrum of the pressure signal preferably is ascertained by a discrete-time Fourier transform (DFT), in particular a discrete-time fast Fourier transform (FFT). The signal processing methods required for this are state of the art.

One embodiment provides that the controller is configured in such a way that at least one spectral component, which is attributable to the imbalance, is ascertained from the amplitude spectrum of the pressure signal, preferably continuously, and the frequency of the at least one spectral component is determined and compared with at least one predetermined limit value, wherein, if the predetermined limit value is exceeded and/or undershot, a control signal is generated that is characteristic of the compaction of the concrete placed in the slipform of the slipform paver or signals a change in the compaction of the concrete placed in the slipform of the slipform paver. The limit value can be ascertained empirically and stored in a memory of the monitoring system. If the value falls below the limit, it can be concluded that the compaction of the concrete is not correct, since the rotational speed of the hydraulic motor is too low, which is why the vibrations are not sufficient. The frequency of at least one spectral component in the amplitude spectrum can also be used to draw conclusions about the state of wear of the concrete compaction device. In principle, it is sufficient if a characteristic parameter is ascertained from the corresponding peak in the amplitude spectrum, which is compared with a reference parameter characteristic of a certain operating state of the concrete compaction device.

In this connection, a preferably continuous ascertainment of at least one spectral component attributable to the imbalance is understood to mean an ascertainment of the spectral component at at least two successive points in time, in order to be able to monitor the concrete compaction device over at least part of the operating time or to be able to make a comparison between a previous point in time and a subsequent point in time, so that a change in the state can be recognized. However, in principle, only a single measurement is possible.

The controller can be configured in such a way that a threshold value for the amplitudes of the harmonics is predetermined for analyzing the pressure signal of the hydraulic motor. Consequently, small amplitudes that lie in the noise range and cannot provide reliable information are filtered out.

In one embodiment, the monitoring system has an output unit that receives the control signal and is designed in such a way that an acoustic and/or optical and/or tactile signal is used to indicate improper compaction of the concrete during operation of the slipform paver if the output unit receives the control signal, because the ascertained frequency is below a predetermined limit value. The monitoring system can also be designed in such a way that an acoustic and/or visual and/or tactile signal is used to indicate proper compaction of the concrete during operation of the slipform paver if the output unit does not receive the control signal, because the ascertained frequency is above a predetermined limit value. If there are multiple concrete compaction devices on the slipform paver, the monitoring system can preferably monitor them individually. If the monitoring system indicates improper compaction with a signal, it can also indicate which of the concrete compaction devices is not being used for proper compaction.

The slipform paver according to the disclosure has at least one hydraulic concrete compaction device having a hydraulic motor for driving a vibration-generating imbalance, which is operated with a hydraulic fluid provided in a hydraulic fluid system, and such a monitoring system.

One embodiment of the slipform paver according to the disclosure provides that the hydraulic fluid system comprises a pressure line leading to the hydraulic motor of the at least one concrete compaction device and a return line leading from the hydraulic motor, and the at least one pressure sensor is arranged in or on the pressure line and/or the return line.

A further embodiment of the slipform paver according to the disclosure provides that the controller of the monitoring system is configured in such a way that the rotational speed of the hydraulic motor of the at least one concrete compaction device is controlled on the basis of an analysis of the pressure signal generated by the at least one pressure sensor.

The controller of the monitoring system can be configured in such a way that a flow control valve provided in the hydraulic fluid system for setting the volume flow of the hydraulic fluid flowing into the hydraulic motor of the at least one concrete compaction device is actuated as a function of the pressure signal correlating with the pressure in the hydraulic fluid in such a way that the concrete compaction device is operated at a predetermined rotational speed. This is the case if the flow control valve is actuated in such a way that the pressure signal correlating with the pressure in the hydraulic fluid, which is measured by the pressure sensor, corresponds to a predetermined value or is within predetermined limit values.

The control signal can also be fed to the central control unit of the slipform paver in order to undertake an intervention in the machine control system. The intervention in the machine control system can involve stopping the slipform paver. The monitoring system according to the disclosure can form a separate assembly with which a conventional slipform paver can be retrofitted. However, the monitoring system can also be part of the slipform paver, wherein the device for monitoring the pressure signal can be part of the central control unit of the slipform paver.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, an exemplary embodiment of the disclosure is explained in more detail with reference to the drawings.

In the drawings:

FIG. 1 shows a side view of a slipform paver with a monitoring system for monitoring the compaction of concrete,

FIG. 2 shows a schematic representation of a monitoring system for monitoring the compaction of concrete together with a hydraulic fluid system for providing hydraulic fluid to drive multiple concrete compaction devices,

FIG. 3 shows the frequency spectrum of the pressure signal of a concrete compaction device over the course of time,

FIG. 4 shows the amplitude spectrum of the pressure signal of a concrete compaction device,

FIG. 5 shows a further frequency spectrum of the pressure signal of a concrete compaction device ascertained during tests, shown over the course of time and

FIG. 6 shows a further amplitude spectrum ascertained during tests.

DETAILED DESCRIPTION

FIG. 1 shows a side view of an exemplary embodiment of a slipform paver without a conveying device, which is described in detail in EP 1 103 659 B1. Since slipform pavers as such belong to the state of the art, only the components of the construction machine that are substantial for the disclosure are described here.

The slipform paver 1 has a machine frame 2, which is supported by a chassis 3. The chassis 3 has two front and two rear steerable running gears 4A, 4B, which are fastened to front and rear lifting columns 5A, 5B. The working direction (direction of travel) of the slipform paver is marked with an arrow A.

The running gears 4A, 4B and the lifting columns 5A, 5B are part of a drive unit of the slipform paver for performing translational and/or rotational movements in the field. The drive unit also includes preferably hydraulic drives, not shown, for the running gears 4A, 4B and an internal combustion engine, not shown. The construction machine can be moved forwards and backwards using the running gears 4A, 4B. By raising and lowering the running gears 4A, 4B via the lifting columns 5A, 5B, the machine frame 2 can be adjusted in height and inclination relative to the floor.

The slipform paver has a slipform 6 for forming concrete, which can be raised or lowered together with the machine frame 2. For compacting the concrete, multiple concrete compacting devices are provided in the slipform, which are immersed in the concrete while the slipform paver is in operation. In FIG. 1, one of the concrete compaction devices 7 is shown schematically in dashed lines.

The concrete compaction device 7 is a hydraulic concrete compaction device, for example a conventional hydraulic internal vibrator. Multiple concrete compaction devices, for example 9 concrete compaction devices, can be provided on the slipform paver, wherein the concrete compaction devices are connected in parallel.

The slipform paver according to the disclosure has a monitoring system 8, shown only schematically in FIG. 1, for monitoring the compaction of the concrete. The monitoring system 8 has an input unit 8A and an output unit 8B, which are provided on an operating console or control panel 9, which is located on the driver's platform 10 in the operator's field of vision.

FIG. 2 shows a schematic representation of an exemplary embodiment of a monitoring system 8 for monitoring the compaction of the concrete together with a hydraulic fluid system 11 for providing hydraulic fluid for driving multiple concrete compaction devices 7 connected in parallel, with the present exemplary embodiment four concrete compaction devices, of which, however, only one concrete compaction device 7 is shown in FIG. 2. The hydraulic fluid system 11 comprises a hydraulic fluid source 12, for example a tank, a central pressure line 14 leading from the hydraulic fluid source 12 to a valve block 13, in which a hydraulic pump 15 is provided for conveying the hydraulic fluid, and a central return line 16 leading from the valve block 13 to the tank 12. In the valve block 13 there are hydraulic flow control valves 17.1, 17.2, 17.3, 17.4 assigned to the individual concrete compaction devices 7 for load-independent control of the volume flow of the hydraulic fluid (hydraulic oil) flowing to the respective concrete compaction device 7. The inlets of the flow control valves 17 are connected to the central pressure line 14, wherein the individual pressure lines 14.1, 14.2, 14.3, 14.4 of the concrete compaction devices 7 are attached to the outlets of the flow control valves 17. The return lines 16.1, 16.2, 16.3, 16.4 of the concrete compaction devices 7 are connected to the central return line 16.

In each case, the hydraulically operated concrete compaction devices 7 have a bottle-shaped or rod-shaped housing 18 in which a hydraulic motor 19 is arranged. The hydraulic motor 19 drives an imbalance shaft 21, which is arranged between bearings 22, via a coupling 20. If the imbalance shaft 21 rotates, its imbalance generates vibrations that are transmitted to the concrete so that the concrete is compacted. The concrete compacting device 7 is fastened to a bracket 23, which has a damping element 24, so that the concrete vibrator can vibrate.

For optimum compaction of the concrete, a certain rotational speed of the imbalance shaft 21 is aimed for. If the rotational speed is too low, the imbalance will be too small, so that the compaction of the concrete is insufficient. Consequently, the rotational speed of the hydraulic motor should be at least between a predetermined upper or lower rotational speed or have a predetermined rotational speed, which is why the hydraulic motor should be operated with a predetermined volume flow. For example, the hydraulic motor 19 achieves a rotational speed of 10,500 rpm at a volume flow of 16 liters/min and a supply pressure of 90 bar.

The monitoring system 8 according to the disclosure enables the monitoring of the rotational speed of the hydraulic motor 19 of one or more concrete compaction devices 7. In addition, the monitoring system 8 according to the disclosure also enables a control of the rotational speed of the hydraulic motor 19 of a concrete compaction device 7.

The structure and mode of operation of the monitoring system 8 is described in detail below.

The monitoring system 8 has pressure sensors 25.1, 25.2, 25.3, 25.4 assigned to the individual concrete compaction devices 7 for measuring the pressure in the hydraulic fluid system 11, which in each case is arranged at a point in the hydraulic fluid system in which particularly strong pressure fluctuations in the hydraulic fluid attributable to the imbalance of the hydraulic motor 19 can be measured. Since a pressure sensor can simply be provided on or in the pressure line, the known slipform pavers can easily be retrofitted with the monitoring system. The pressure sensor 25.1, 25.2, 25.3, 25.4 can, for example, be a pressure transducer with strain gauges or a capacitive or piezoelectric pressure transducer. The pressure sensor converts the mechanical variable of pressure P(t) into a proportional electrical current signal I(t) of, for example, 4 to 20 mA. This pressure signal can be tapped as a voltage U via a resistor R.

With the present exemplary embodiment, the pressure sensors 25.1, 25.2, 25.3, 25.4 assigned to the individual concrete compaction devices 7 are arranged in or on the pressure line 14.1, 14.2, 14.3, 14.4 of the respective concrete compaction device 7 downstream of the valve block 13. However, the pressure sensors can also be provided on the return lines 16.1, 16.2, 16.3, 16.4 of the concrete compaction devices 7.

In addition, the monitoring system 8 has an evaluation unit 26 for analyzing the pressure signal P(t) of each pressure sensor 25.1, 25.2, 25.3, 25.4, which is connected to the pressure sensors via signal lines S1, S2, S3, S4, in order to receive the measurement signals of the pressure sensors, and an input unit 8A and an output unit 8B, so that the human operator can input instructions and information can be output. The input unit 8A can, for example, comprise a keyboard, a joystick or another user interface and the output unit 8B can comprise a screen and/or signal lamps. The input and output unit 8A, 8B can also be a touch-sensitive screen (touchscreen), which is provided in a control panel 10.

The controller 26 for analyzing the pressure signal P(t) comprises at least one low-pass filter 33 (anti-aliasing filter) and an analog-to-digital converter 27 (ADC), which receives the analog measurement signals. The analog/digital converter 27 converts the analog measurement signal into a digital signal. Since the measurement signal passing through the low-pass filter is sampled by the analog-to-digital converter 27, aliasing effects can occur, which can be prevented by means of the low-pass filter 33, whose filter characteristic is to be adapted to the occurring interference and the useful signal. The minimum sampling frequency is determined by the Nyquist-Shannon sampling theorem

$\begin{array}{cc}{f}_{\mathrm{abtast}}>2f_{\max }& \left(\mathrm{Equation}1\right)\end{array}$

With the present exemplary embodiment, the sampling frequency is 10 KHz. Furthermore, the controller 26 comprises at least one high-pass filter 31, for example with a cut-off frequency of 10 Hz, in order to filter the measurement signals of the pressure sensors 25.1, 25.2, 25.3, 25.4 so that the noise in the low-frequency range is suppressed. The measurement signals of the pressure sensors 25.1, 25.2, 25.3, 25.4 can be filtered and converted in this way by the controller 26, either simultaneously or sequentially.

The controller 26 for analyzing the pressure signal further comprises a processor 28 and a computer-readable medium 29 and a database 30 or can cooperate therewith.

It is understood that the controller 26 can be a single control device (controller) with all the functions described or can comprise multiple controllers, wherein the functionality described is distributed among the controllers. Different operations, steps or algorithms as described in this connection can be embodied directly in hardware, in a computer program product, for example in a software module executed by the processor, or in a combination of both. The computer program product can reside in a RAM memory, a flash memory, an ROM memory, an EPROM memory, an EEPROM memory, registers, a hard disk, a removable storage medium or any other form of computer-readable medium known in the art. An exemplary computer-readable medium can be connected to the processor in such a way that the processor can read information from the memory/storage medium and write information to the memory/storage medium. Alternatively, the medium can be integrated into the processor. The processor and the medium can be located in an application-specific integrated circuit (ASIC). The ASIC can be located in a user terminal device. Alternatively, the processor and the medium can be located in a user terminal device as discrete components. The term “processor” as used herein can refer to at least general purpose or special purpose processing devices and/or logic as understood by those skilled in the art, including, but not limited to, a microprocessor, a microcontroller, a state machine or the like. A processor can also be implemented as a combination of computing devices, for example as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core or other such configuration.

The controller 26 for analyzing the pressure signal is configured in such a way that the method steps described below are carried out.

The controller 26 initially transforms the digital pressure signal P(t) of each pressure sensor 25.1, 25.2, 25.3, 25.4 from the time domain into the frequency domain, in order to be able to analyze the frequency spectrum. The amplitude spectrum is of particular interest for monitoring the pressure signal.

The transformation from the time domain to the frequency domain is carried out using a discrete-time, fast Fourier transformation (FFT/DFT). The algorithms required for this purpose are known to the person skilled in the art. Corresponding software can be implemented for this purpose.

FIG. 3 shows the amplitude spectra of the pressure signal over the measurement time, which were ascertained in tests during the operation of a conventional internal vibrator. The frequency in kHz is plotted on the abscissa and the measurement time in s is plotted on the ordinate. The pressure in mbar is represented by different gradations. During the measurement, the rotational speed of the hydraulic motor 19 of the internal vibrator was increased and reduced again using an adjustment device provided for this purpose. In the measurement result, this progression can be recognized as a curve marked I in FIG. 3. The first harmonics of the individual fundamental frequencies can also be seen (marked II). The piston frequency f_k of the hydraulic pump can be found in the straight line marked III. The straight line marked IV contains the first harmonic of the piston frequency f_k of the hydraulic pump, which can be calculated as follows using equation 2:

$\begin{array}{cc}\mathrm{fk}=\mathrm{Nk}·n& \left(\mathrm{Equation}2\right)\end{array}$

With the present number of pistons N_k of 9 and a pump rotational speed n of 2039 rpm (converted approximately 33.98 r/s), this results in a piston frequency f_k of the hydraulic pump of 305.85 Hz. This result coincides with the position of straight line III.

FIG. 4 shows an individual amplitude spectrum calculated from the measured pressure values from approximately 6 s after the start of the measurement. The frequency of 307.6 Hz of the peak marked III again corresponds to the piston frequency fk of the hydraulic pump 15 and the frequency of the peak marked IV corresponds to the first harmonic of the piston frequency fk of the hydraulic pump 15.

The controller 26 of the monitoring system 8 is configured in such a way that the peak I attributable to the imbalance is filtered out of the amplitude spectrum and the frequency of this peak is ascertained, which corresponds to the rotational speed of the hydraulic motor 19 of the concrete compaction device 7. In the amplitude spectrum in FIG. 4, this frequency is 102.5 Hz. It is to be taken into account that the peak corresponding to the rotational speed of the concrete vibrator is not always the peak with the highest amplitude. For example, the peak of the piston frequency fk of the hydraulic pump 15 can have a greater amplitude than the peak corresponding to the rotational speed of the concrete vibrator. A data processing program runs on the hardware of the controller 26, which program contains an algorithm that filters out the peak whose frequency corresponds to the rotational speed of the vibrator from the individual amplitude spectra with the aid of corresponding filter techniques.

The discrete-time, fast Fourier transform (FFT/DFT) requires a finite number of measured values. Since the measurement signal is recorded continuously, a time window is cut out of the measurement signal. If the window width is not a multiple of the period duration of the signal, a jump occurs between the first and the last sampled value, since the signal continues periodically. The jump creates additional frequencies in the frequency spectrum that are not present in the signal. This effect is known as the leakage effect (Meyer, Martin: Analoge und digitale Signale, Systeme und Filter, 8th edition, Wiesbaden: Springer Vieweg 20179). In order to avoid this effect, the signal is weighted with a window function in this exemplary embodiment. Due to the leakage effect, the frequencies occurring in the signal are not sharp current peaks in the amplitude spectrum, but a main lobe is created at the frequency, which is surrounded by multiple side lobes. For an oscillation with a high amplitude, the side lobe response can be higher than that of the main lobe of a neighboring oscillation, causing it to disappear into the noise. By varying the window function, the shape of the main lobe and the side lobes can be changed, so that the largest possible number of relevant frequencies can be reliably detected.

When analyzing the pressure signal, various window functions that influence the frequency spectrum differently can be used. For this reason, a window function whose properties are adapted to the desired spectrum should be selected. The Hamming window with a window width of 2¹¹ measuring points was used for the measurement results shown in FIG. 3 and FIG. 4. However, other window functions and widths can also be used. It should be noted that the resolution Δf in the frequency domain is influenced as a function of the sampling frequency f_abtast and the window width N according to equation 3. With a present sampling frequency of 10 KHz and a window width of 2¹¹, this results in a frequency resolution of approximately 4.88 Hz.

$\begin{array}{cc}\Delta f=f_{\mathrm{abtast}}/N& \left(\mathrm{Equation}3\right)\end{array}$

In further tests, two hydraulic lines were firmly fixed to a concrete vibrator, which were pre-tensioned to a pressure of 15 bar using a hand pump. Subsequently, the rotational speed of the vibrator was slowly increased. FIG. 5 shows the frequency spectrum over the course of time, wherein the increase in vibrator rotational speed and other harmonic oscillations can be recognized. FIG. 6 shows the amplitude of the pressure change over the frequency. It can be seen that the amplitude also increases with increasing frequency. This is due to the fact that acceleration increases with increasing rotational speed.

On a slipform paver, a monitoring system 8 with multiple pressure sensors 25.1, 25.2, 25.3, 25.4 can be provided for monitoring multiple hydraulic concrete compaction devices 7, in order to determine the rotational speed of each individual concrete compaction device, as described above, or multiple monitoring systems with only one pressure sensor can be provided for monitoring only one of the concrete compaction devices. The rotational speed of the hydraulic motor can be determined simultaneously or successively from the measurement signal of the pressure sensors attached to the monitoring system. The recorded rotational speeds of the hydraulic motors of the individual concrete compaction devices can be sent cyclically via a CAN interface. The CAN messages can be visualized on the output unit 8B. For example, the rotational speeds of the hydraulic motors can be displayed on the output unit 8B.

The monitoring system 8 can also have a plurality of digital outputs for actuating signal lamps 32 provided on the output unit 8B, wherein a signal lamp can be assigned to each concrete compaction device. One exemplary embodiment is that a red signal lamp, which is assigned to a concrete compaction device, is switched on if the rotational speed of the hydraulic motor of this concrete compaction device falls below a defined threshold value for a certain period of time.

With the present exemplary embodiment, the monitoring system 8 also functions as a control device that generates control signals for actuating the flow control valves 17.1, 17.2, 17.3, 17.4 for setting the volume flow of the hydraulic fluid for driving the concrete compaction devices 7. The control signals are transmitted from the evaluation unit 26 via control lines R1, R2, R3, R4 to the flow control valves 17.1, 17.2, 17.3, 17.4. The controller 26 is configured for controlling the flow control valves in such a way that the flow control valves are actuated as a function of the pressure signal P(t) correlating with the pressure in the hydraulic fluid, which is generated by the respective pressure sensor 25.1, 25.2, 25.3, 25.4, in such a way that the relevant concrete compaction device 7 is operated at a predetermined rotational speed. If the rotational speed of the hydraulic motor 19 of a concrete compacting device 7 decreases, for example due to a loss of oil, the controller 26 generates a control signal that causes an increase in the volume flow of the hydraulic fluid flowing to the hydraulic motor of the concrete compacting device. Consequently, the volume flow is controlled in such a way that the rotational speed of the hydraulic motor corresponds to a predetermined value, wherein the control deviation should be minimal. This ensures optimum compaction of the concrete over the service life of the concrete compaction device.

Claims

1. A slipform paver, comprising: a slipform configured to form a concrete structure from concrete;at least one hydraulic concrete compaction device including a hydraulic motor for driving a vibration-generating imbalance;a hydraulic fluid system configured to provide a hydraulic fluid to the hydraulic motor; anda monitoring system for monitoring a compaction of the concrete, the monitoring system including: at least one pressure sensor arranged in the hydraulic fluid system, and configured to generate a pressure signal correlated to a pressure in the hydraulic fluid; anda controller configured to receive the pressure signal and to evaluate the compaction of the concrete based on an analysis of the pressure signal.

2. The slipform paver according to claim 1, wherein the controller is configured such that an amplitude spectrum of the pressure signal is determined for analyzing the pressure signal.

3. The slipform paver according to claim 2, wherein the controller is configured such that the pressure signal is sampled, and the amplitude spectrum of the pressure signal is ascertained by a discrete-time Fourier transform (DFT).

4. The slipform paver according to claim 3, wherein the discrete-time Fourier transform (DFT) is a discrete-time fast Fourier transform (FFT) of the pressure signal.

5. The slipform paver according to claim 2, wherein the controller is configured such that: at least one spectral component, which is attributable to the imbalance, is ascertained from the amplitude spectrum of the pressure signal, and a frequency of the at least one spectral component is determined and compared with at least one predetermined limit value; anda control signal is generated if the at least one limit value is exceeded and/or undershot.

6. The slipform paver according to claim 5, wherein the controller is configured such that a threshold value for an amplitude of a harmonic of the pressure signal is predetermined for evaluating the pressure signal.

7. The slipform paver according to claim 5, wherein the controller includes an output unit configured to receive the control signal and configured such that an improper compaction of the concrete during operation of the slipform paver is indicated by an acoustic and/or optical and/or a tactile signal, if the output unit receives the control signal, or that proper compaction of the concrete during operation of the slipform paver is indicated by an acoustic and/or optical and/or tactile signal if the output unit does not receive the control signal.

8. The slipform paver according to claim 1, wherein the hydraulic fluid system comprises a pressure line leading to the hydraulic motor of the concrete compaction device and a return line leading from the hydraulic motor, and the at least one pressure sensor is arranged in or on the pressure line and/or the return line.

9. The slipform paver according to claim 1 wherein the controller is configured such that a rotational speed of the hydraulic motor of the at least one concrete compaction device is controlled based at least in part on the analysis of the pressure signal generated by the at least one pressure sensor.

10. The slipform paver according to claim 9, wherein: the hydraulic fluid system includes a flow control valve for setting a volume flow of the hydraulic fluid flowing into the hydraulic motor of the at least one concrete compaction device; andthe controller is configured such that the flow control valve is actuated as a function of the pressure signal such that the concrete compaction device is operated at a predetermined rotational speed.

11. A method of monitoring a compaction of concrete placed in a slipform of a slipform paver with at least one hydraulic concrete compaction device, which has a hydraulic motor for driving a vibration-generating imbalance, which is operated with a hydraulic fluid that is provided in a hydraulic fluid system, the method comprising: measuring a pressure in the hydraulic fluid using at least one pressure sensor arranged in the hydraulic fluid system, which pressure sensor generates a pressure signal correlating with the pressure in the hydraulic fluid; anddetermining the compaction of the concrete placed into the slipform of the slipform paver based at least in part on an analysis of the pressure signal.

12. The method according to claim 11, wherein the analysis of the pressure signal includes determining an amplitude spectrum of the pressure signal by a discrete-time Fourier transform (DFT).

13. The method according to claim 12 wherein the discrete-time Fourier transform (DFT) is a discrete-time fast Fourier transform (FFT).

14. The method according to claim 12, wherein at least one spectral component, which is attributable to the imbalance, is ascertained from the amplitude spectrum of the pressure signal and the frequency of the at least one spectral component is determined and compared with at least one predetermined limit value, wherein a control signal is generated if the predetermined limit value is exceeded and/or undershot and an acoustic and/or optical and/or tactile signal is used to indicate improper compaction of the concrete during operation of the slipform paver if the control signal is generated, or an acoustic and/or optical and/or tactile signal is used to indicate proper compaction of the concrete during operation of the slipform paver if the control signal is not generated.

15. The method according claim 11, wherein a rotational speed of the hydraulic motor of the at least one concrete compacting device is controlled on the basis of the analysis of the pressure signal generated by the at least one pressure sensor.

16. The method according to claim 15, wherein a flow control valve is included in the hydraulic fluid system for setting the volume flow of the hydraulic fluid flowing into the hydraulic motor of the at least one concrete compacting device, the method further comprising: actuating the flow control valve as a function of the pressure signal correlating with the pressure in the hydraulic fluid such that the concrete compacting device is operated at a predetermined rotational speed.