Abstract:
A tamping device comprises a drive motor which, via a spring mechanism, drives a soil contact element for compacting the soil. A detection device records the speed of rotation of the drive motor. An evaluation device evaluates the dynamic response of the speed of rotation and recognizes an aperiodic response. A control device prompts a change in the speed of rotation of the motor if an aperiodic response has been recognized.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a tamping device for soil compaction. 
         [0003]    2. Description of the Related Art 
         [0004]    A tamping device of this type, also called a tamper in the text which follows, is known in various embodiments, for example from DE 44 45 188 A1 or DE 197 39 743 A1. 
         [0005]    The basic principle involves a rotary movement of a drive motor being converted into an oscillating linear movement which is transmitted to a soil contact element, for example a tamping foot, by means of a spring system. The tamper has an upper mass which comprises, inter alia, the drive motor, a part of a crank mechanism, housing elements and bearings. A lower mass is movably coupled to the upper mass by means of a spring device, said lower mass comprising the soil contact element for soil compaction. The crank mechanism converts the rotary movement of the drive motor into a linear reciprocating movement which is transmitted to the lower mass, and therefore to the soil contact element, by the spring device, in particular by means of a double-acting spring system. An example of the spring device is shown in DE 197 39 743 A1. 
         [0006]    A periodic, oscillating movement is imposed on the soil contact element by the movement of the crank mechanism. This periodic movement is also ideally maintained during soil compaction. In this case, the soil can be compacted particularly effectively. 
         [0007]    However, it has been found that tampers can usually be optimally designed only for a specific soil structure or stiffness, and therefore the periodic movement can be at least approximately achieved, and therefore effective compaction can be realized, for some soil structures, whereas for other soils it is only possible to achieve compaction to a limited degree on account of a response which is no longer periodic. The result is, for example, that a tamper compacts the soil uniformly on uncompressed, compactable ground, whereas it falls “out of step” as the soil density increases. This can lead, for example, to an idle stroke following two working strokes of the tamping foot because the spring/mass system, which is formed by the tamper and the soil, is no longer synchronized. An idle stroke takes place particularly when, during the previously effective stroke, such a great rebound force acts on the lower mass that the entire tamper is pushed high above the ground in such a way that the soil contact plate can no longer reach the soil in the following cycle. 
         [0008]    In the case of asynchronous, aperiodic operation, the passive system (upper mass, guide handle) reacts with high amplitudes, and this can lead to losses in the ability to control the tamper. In this case, the operator is subject to high loads while operating the tamper, while the device operates with only a low degree of efficiency. Hand/arm acceleration reaches high values, and this reduces the usage time of the device. 
         [0009]      FIGS. 5 and 6  show examples of synchronous, periodic operation ( FIG. 5 ) and asynchronous, aperiodic operation ( FIG. 6 ) of a tamper. Said figures each illustrate the amplitude profiles with respect to time for the tamping foot which forms part of the lower mass, the crankcase which forms part of the upper mass, and the handle, which likewise forms part of the upper mass but is usually spring-cushioned. The harmonic movements of the foot, crankcase and handle during the periodic operation shown in  FIG. 5  can be clearly identified, while the asynchronous operation shown in  FIG. 6  leads to a stochastic movement response of the components of the tamper. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention is based on the object of providing a tamping device with which uniform, periodic operation is possible even with different soil structures. 
         [0011]    According to the invention, the object is achieved by tamping devices according to claims  1  and  3 . Advantageous refinements of the invention are defined in the dependent claims. 
         [0012]    As is known, a tamping device has a drive motor, an upper mass which accommodates or comprises the drive motor, a lower mass which is movably coupled to the upper mass by means of a spring device and which has a soil contact element for soil compaction, and a movement transmission device for transmitting a drive movement from the drive motor and generating a periodic movement of the soil contact element. Also provided is a detection device for detecting a measurement parameter for the dynamic response of at least one component of the tamping device. An evaluation device serves to evaluate the dynamic response and to identify an aperiodic response. An indicator device can be used to indicate that an aperiodic response is identified by the evaluation device. 
         [0013]    Possible components of the tamping device are various subregions and structural elements, for example the motor shaft, a crankshaft which forms part of the crank mechanism, connecting rods, upper mass housing, tamping foot with soil contact element, guide handle etc. 
         [0014]    Therefore, a measurement parameter, which serves as a criterion for the dynamic response of the component in question, but possibly also of the entire tamping device, is permanently detected during operation of the tamping device. In an ideal case, the measurement parameter should record a periodic response in accordance with the likewise periodic excitation by the movement transmission device, that is to say a crank mechanism for example. If, however, the evaluation device determines that the measurement parameter, and therefore the actual dynamic response, deviates from a substantially uniform, for example sinusoidal, periodic response, this is considered to be a criterion for an aperiodic response. This can be used to draw the conclusion that the tamper is not operating in an optimum manner and therefore the operator is prompted to make changes. The operator is then informed by means of the indicator device that an aperiodic response is present. 
         [0015]    Static or dynamic rules can be stored in the evaluation device, for the purpose of defining action recommendations for the user, in particular how he should change the rotation speed of the drive motor in order to reduce the aperiodic response. The evaluation device is statically or dynamically able to select a suitable action recommendation as a function of the identified aperiodic response and to output this by means of the indicator device. In this way, the operator can be advised to increase or reduce the rotation speed in order to again achieve an at least approximately periodic response of the tamper and therefore synchronous interaction between the tamper and soil. 
         [0016]    In one variant, the tamping device has a control device for changing at least one dynamic parameter of at least one of the components of the tamping device when an aperiodic response is identified by the evaluation device. In this case, it is not necessary for the operator to be informed about the aperiodic response and take control measures, for example change the rotation speed. Instead, the control device automatically carries out suitable measures itself in order to again achieve a periodic, synchronous response in the event of an aperiodic response. If the control device implements these measures continuously or at very short intervals, the operator will not notice them at all. 
         [0017]    It goes without saying that it is possible to provide an indicator device in this variant too, in order to inform the operator that an aperiodic response is identified by the evaluation device. However, it is also possible for the dynamic parameter to be changed or the control measures to be implemented without the operator being informed. The indicator device is not required in this case. 
         [0018]    The vibration response of the tamper can be determined by a suitable measurement parameter which is selected from the group comprising rotation speed of the drive motor, load surges on a motor shaft of the drive motor, rotation speed of the movement transmission device, movement response of the monitored component in question, relative movement between the upper mass and the lower mass, acceleration of the component in question, acceleration of the upper mass, acceleration of the lower mass, acceleration of a guide handle which is mounted on the upper mass, and rotation angle between the guide handle and the upper mass. 
         [0019]    The load surges on the motor shaft of the drive motor change the motor rotation speed, and this change can be detected relatively easily. The surges are the result of intermittent power consumption by the tamping system and lead to a periodic change in the motor rotation speed. In the case of regular exchange of force between the tamping foot (soil contact element) and the soil, the changes in rotation speed are significant, unlike in the case of idle strokes of the tamping system which can arise in the event of an aperiodic response. As long as the motor rotation speed changes periodically, the evaluation device assumes correct operation. If, in contrast, there are deviations from the periodic change, that is to say an aperiodic response is consequently determined, corresponding measures can be taken. 
         [0020]    In addition or as an alternative to the rotation speed, the movement response or the acceleration of a suitable component of the tamper can also be detected and evaluated. In addition, it may be expedient to also detect and evaluate the rotation angle of the guide handle relative to the upper mass. 
         [0021]    In a simple embodiment, it is sufficient to detect just one measurement parameter. However, depending on the desired degree of accuracy, it may also be expedient to evaluate a plurality of measurement parameters, for example also using a plurality of measurement sensors (rotation speed sensor, acceleration sensor etc.) in order to obtain the most precise picture of the movement response of the tamper possible. 
         [0022]    The dynamic parameter is selected from the group comprising rotation speed of the drive motor, torque of the drive motor, spring stiffness of the spring device between the upper mass and the lower mass, and damping properties of a damping device which is arranged between the upper mass and the lower mass. 
         [0023]    Changing the rotation speed of the drive motor is the simplest way of influencing the dynamic response of the tamping device. The rotation speed can be changed manually by the operator, when said operator is provided with a corresponding action recommendation by the indicator device, but it is also possible for the control device to automatically change the rotation speed of the drive motor in a suitable manner when an aperiodic response is determined. 
         [0024]    As an alternative or in addition to this, the spring stiffness of the spring device which couples the upper mass and the lower mass can also be changed. Suitable devices for this purpose are known from many fields of technology, for example from automotive engineering. It is also possible to take action in the damping system of the tamper. For example, the spring device generally also has damping properties which can be changed, for example, by actuable active damping elements between the upper mass and the lower mass. 
         [0025]    It is possible, likewise as an alternative or in addition, to adjust the oscillation amplitude of the soil contact element, that is to say in particular the jump height of the tamping foot. This is possible, for example, by adjusting the transmission response of the movement transmission device. For example, the crank radius of the tamping drive can be adjusted in order to change the travel for excitation of the spring system which serves to transmit movement. 
         [0026]    It is also possible to change the oscillation frequency of the soil contact elements. In this case, it is possible to adjust, for example, the transmission ratio between the drive motor and the movement transmission device so that the frequency of the tamping movement is changed while the motor rotation speed remains unchanged. It goes without saying that it is also possible to change both the motor rotation speed and the transmission ratio in order to change the oscillation frequency overall. 
         [0027]    The cited ways of defining the dynamic parameter can be implemented individually or else in combination. In this case, it is possible for the measures to act to the same effect, but also to the opposite effect. For example, it is feasible for the crank radius to be reduced and at the same time for the motor rotation speed and/or the tamping frequency to be increased. 
         [0028]    An aperiodic response can be identified particularly when the correspondingly provided measurement parameter deviates from an ideally periodic response by a predefined amount. The ideally periodic response should be predefined in such a way that it can be achieved without problems during normal, effective operation of the tamper. Deviations from this ideally periodic response within the predefined amount are permissible. An aperiodic response is assumed, and therefore the corresponding measures are taken, only if the tolerance range is transgressed. 
         [0029]    In one embodiment, the drive motor is a gasoline engine, in which case the rotation speed, which can be changed as the dynamic parameter, is a rated or limit rotation speed. 
         [0030]    Mechanical and electronic rotation speed controllers are used to regulate the rated or limit rotation speed in gasoline engines, said rotation speed controllers using the rotation speed to influence assemblies (throttle or ignition characteristic map in internal combustion engines) which determine power and rotation speed, in order to prevent the rotation speed from rising above the predefined limit rotation speed and/or to keep said rotation speed at the predefined rated rotation speed. Depending on the load, the opening of the throttle, the ignition angle and the duty cycle of the ignition means are adjusted such that the rotation speed regulation difference is minimal. 
         [0031]    Incidentally, the drive motor can analogously also be an electric motor which has, for example, an electronic rotation speed controller in the form of a voltage or frequency regulator. 
         [0032]    The regulators mentioned above in connection with the gasoline engine operate statically in conventional tamper drive motors. The characteristic map of said regulators is defined by dimensioning of the centrifugal weights, the springs etc., or by prespecifying the ignition characteristic map, and serves to maintain a specific rotation speed. Manual or adaptive variation of the level of the regulated limit rotation speed (and therefore of the drive frequency of the tamper) is not available, either manually or electronically, in the prior art. 
         [0033]    In said embodiment however, the limit rotation speed can be changed in order to influence the drive frequency of the tamper. 
         [0034]    The gasoline engine can have a characteristic map-controlled ignition device, the rotation speed of the gasoline engine having to be kept constant substantially at the value of the limit rotation speed by the ignition device, with the aid of a variation in an ignition time. 
         [0035]    The control device can be formed in such a way that the rotation speed of the drive motor is changed in accordance with predefined rules when an aperiodic response of the motor shaft is identified. 
         [0036]    The rules can be stored in the evaluation device, for example in the form of prespecifications which prescribe a specific control measure when an aperiodic response occurs, and also by characteristic curves, characteristic maps and/or predefined operating points on characteristic curves or characteristic maps. 
         [0037]    Therefore, rules are predefined in the evaluation device and these rules are implemented by the control device when an aperiodic response has been identified. Implementing these rules can mean slowly linearly raising or lowering the limit rotation speed of the drive motor. It is also possible to deliberately set specific operating points on the respectively associated characteristic curve or the characteristic maps, which operating points can be predefined in advance by the manufacturer. For example, it is possible to predefine, outside the normal operating point, a further three to five alternative operating points which are set—under certain circumstances in succession—by the control device in order to test whether the vibration response of the tamper has improved. In the process, it has been found that the periodic tamper response can be improved in most cases. 
         [0038]    These and further advantages and features of the invention will be explained in greater detail below with reference to an example, with the aid of the accompanying figures 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  shows an example of a tamper according to the invention; 
           [0040]      FIG. 2  shows a mechanical equivalent circuit diagram of the tamper from  FIG. 1 ; 
           [0041]      FIG. 3  shows a schematic illustration of the design of the tamping device; 
           [0042]      FIG. 4  shows a two-dimensional characteristic map for a tamper with a gasoline engine; 
           [0043]      FIG. 5  shows the vibration response of components of a tamper in the case of synchronous-periodic operation; and 
           [0044]      FIG. 6  shows the movement response of the components in the case of asynchronous-aperiodic operation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]      FIG. 1  shows a side view of a typical tamper having an upper mass  1  and a lower mass  2  which comprises a tamping foot  3  which serves as the soil contact element. A drive motor  4  forms part of the upper mass  1  and is in the form of a gasoline engine. A guide handle  5  is elastically attached to the upper mass  1 , it being possible for the operator to control the tamper using said guide handle and said guide handle being fitted with a fuel tank  6 . 
         [0046]    A housing  7 , which forms part of the upper mass  1 , contains, in a known manner, a crank mechanism which converts the rotary movement of the drive motor  4  into an oscillating linear movement which is transmitted to the lower mass  2 , and finally to the tamping foot  3 , by means of a spring system (not illustrated) which is known per se. 
         [0047]      FIG. 2  shows a simplified schematic illustration of the tamper, said figure also showing a spring device  8  which couples the upper mass  1  to the lower mass  2 . 
         [0048]      FIG. 3  shows a further simplified illustration of the tamper in the form of the drive motor  4  which drives a connecting rod  10  by means of a crankshaft  9 , the linear reciprocating movement of said connecting rod being transmitted to the lower mass  2  by means of the spring device  8 . 
         [0049]    The rotary movement or rotation speed of the crankshaft  9 , which is simultaneously a motor shaft  4   a  of the drive motor  4  in the example shown, is detected by a rotation speed sensor  11 . It goes without saying that other embodiments are also feasible, in which the motor shaft  4   a  of the drive motor  4  first drives a gear mechanism, which is finally coupled to the crankshaft  9 . 
         [0050]    Conventional measurement sensors are suitable for use as the rotation speed sensor  11 . The information about the rotation speed response can likewise also be obtained by monitoring the ignition means etc. Therefore, it is also possible to use a control processor of the ignition system of the drive motor  4  to obtain information about the rotation speed response of the motor shaft  4   a  or of the crankshaft  9 . The aim here is to detect and to observe the change in the rotation speed in the drive train on the basis of the load surges which occur while the tamper is in use. 
         [0051]    Therefore, it is not absolutely necessary to provide a dedicated rotation speed sensor  11 . 
         [0052]    The corresponding measurement signal from the rotation speed sensor  11  or an alternative item of information is delivered to a detection device  12  which detects the dynamic response of the crankshaft  9  or of the motor shaft  4   a.    
         [0053]    A corresponding item of information is passed from the detection device  12  to an evaluation device  13  which identifies an aperiodic response by evaluating the dynamic response. If the evaluation device  13  identifies the aperiodic response of the tamper, as shown in  FIG. 6  by way of example, said evaluation device can indicate this by means of an indicator device  14 . Said evaluation device can also forward the information to a control device  15  which actuates an ignition system  16  of the drive motor  4 , in accordance with predefined rules, in order to change the rotation speed. The dynamic response of the tamper is changed by changing the rotation speed, said changed dynamic response ideally improving the periodic response, so that a movement response as shown in  FIG. 5  by way of example can be achieved. 
         [0054]    Instead of the control device  15 , it is also possible to use the indicator device  14  merely to inform the operator that an aperiodic response has been determined. If desired, the operator can be provided with action recommendations as to which measures should be taken in order to reduce the aperiodic response. By way of example, two light-emitting diodes, which are marked “plus” and “minus”, can be used to prompt the operator to increase or to lower the rotation speed by operating the accelerator lever. 
         [0055]      FIG. 4  shows various characteristic curves or two-dimensional characteristic maps which define the ignition time as a function of the motor rotation speed. The characteristic maps are identical in a range from 0 to approximately 3700 rpm. However, in the operating range, which is important for operation, of between 3700 and 5000 rpm, four characteristic maps are spread out by virtue of corresponding characteristic curves and thus define a different response. 
         [0056]    The evaluation device  13  or the control device  15  selects either operating points within a characteristic map or operating points which are predefined for various characteristic maps, which operating points can be set when an aperiodic response is identified. The dynamic response of the tamper can be changed until the periodic response is improved, possibly by automatically “trying out” various operating points or by departing from the characteristic curves. 
         [0057]    An ignition system which is controlled by a characteristic map on this basis is suitable, for example, for two-stroke motors in which the limit rotation speed of the motor is maintained by varying the ignition time. The only input variable used is the cycle period of the fan impeller, which is mounted on the crankshaft and has a magneto, from which electrical signals are obtained in the magneto ignition, and these signals are used as a criterion for the rotation speed and replace the signal from a rotation speed sensor  11 , so that said rotation speed sensor can be dispensed with. 
         [0058]    The motor rotation speed and the current angular position of the crankshaft  9  in relation to the top dead center of a piston in the internal combustion engine  4  are obtained from the electrical signals obtained from the magneto ignition. In a suitable two-dimensional characteristic map according to  FIG. 4 , the angle relative to the top dead center of the motor  4  is predefined for the ignition process. 
         [0059]    The tamper is matched to its ambient conditions with the aid of adaptive influencing of the drive rotation speed of the drive motor  4  of the tamper. This leads to optimum operating results and quiet operation even in the case of highly compacted soils. The hand/arm vibrations are reduced as a result, while the ability to control the tamper is improved, even in the case of cohesive soils.