Working machine having grab bucket, in particular underground diaphragm wall grab bucket

Abstract

The invention relates to a working machine, in particular a cable excavator or special deep foundation construction equipment, comprising: a grab bucket, in particular an underground diaphragm wall grab bucket, suspended on the working machine by means of a cable; the cable rope is installed on the cable rope winch so that the grab bucket can move, and the grab bucket can be rolled up and unfolded; a first measuring device, by means of which a closing variable representing a closing force acting during the excavation process when the grab shovel is closed can be detected; and a control unit connected to the first measuring device, by means of which the cable winch is actuated. The control unit is arranged to control or adjust the cable winch according to a set value during the digging process, so that the grab bucket is kept under a predetermined residual tension, and the set value is changed according to the detected closing variable. The invention further relates to a method for carrying out a mining process by means of the working machine according to the invention and to a corresponding computer program product.

Description

Technical Field

[0001] This invention relates to a working machine and a method and computer program product for carrying out an excavation process by means of said working machine. Background Technology

[0002] Hydraulic or mechanical grabs are used in a variety of applications, such as in cable shovel excavation, grab loading and unloading, and special deep foundation construction. In the latter, grab schemes are sometimes used as an alternative to diaphragm wall milling in the form of hydraulic or mechanical diaphragm wall grabs. In these twin-shovel grabs, the opening and closing of the grab shovels is carried out either via one or more hydraulic cylinders (hydraulic closing cylinders) or via a cable system by means of retaining and closing cables provided for this purpose.

[0003] Diaphragm walls are particularly used in the construction of special deep foundations to stabilize excavations. To construct such a diaphragm wall, a vertical diaphragm wall is typically excavated from the bottom along a guide wall, followed by the pouring of reinforced concrete. The resulting diaphragm wall provides support for further foundation construction of the building. Typically, the diaphragm wall grab bucket is suspended by one or more cables (usually traction cables in hydraulic diaphragm wall grab buckets, and a combination of traction cables and closed cables in mechanical diaphragm wall grab buckets) from a load-bearing device, typically a cable excavator with a pivotable cantilever or a special deep foundation construction equipment with a mast.

[0004] In this type of machinery, it is known that the static residual tension is adjusted during active free fall so that the grab bucket is not completely afloat during excavation, but is held in place by the adjusted residual tension via a winch (cable winch) used for traction. However, this approach does not take into account different soil types and bulk material characteristics, thus holding the grab bucket components with excessively high or low residual tension. Summary of the Invention

[0005] The purpose of this invention is to improve this type of working machinery to optimize the digging process. In particular, it will improve the efficiency and ease of operation of the grab bucket closing process.

[0006] This objective is achieved by a machine tool according to one aspect of the invention, by a method according to another aspect of the invention, and by a computer program product according to yet another aspect of the invention. Other aspects of the invention are advantageous embodiments as described below.

[0007] Therefore, a working machine is proposed, comprising a grab bucket suspended from the working machine by at least one cable, particularly suspended from the cantilever or mast of the working machine. The working machine may, in particular, be a cable excavator or a specialized deep foundation construction equipment. The grab bucket comprises at least two openable and closable grab shovels, and is preferably designed as a double-shovel grab bucket.

[0008] The grab bucket can be designed as a mechanical grab bucket, particularly a diaphragm wall grab bucket, in which the working machinery comprises multiple cables and corresponding cable winches. The grab bucket is suspended from the working machinery by the cables, which are wound and unwound on the cable winches in a retractable and deployable manner to adjust or move the grab bucket spatially and to open and close the grab bucket shovel. The cables can be traction cables and closing cables, as known from known grab bucket designs, particularly from known mechanical diaphragm wall grab buckets. The cable winches are, in particular, actuable independently of each other.

[0009] Alternatively, the grab bucket can be designed as a hydraulic grab bucket, particularly a diaphragm wall grab bucket, wherein the working machinery in this case includes a cable (traction cable) and a cable winch (traction winch) on which the cable is mounted in a retractable and deployable manner to adjust or move the grab bucket in space. In this case, the grab bucket shovel is opened and closed by at least one, preferably two, hydraulic closing cylinders, which are specifically arranged on or inside the grab bucket.

[0010] In the case of hydraulic grabs, the grab can also be held in place by more than one cable, wherein multiple cable winches are actuated synchronously to move the grab. In this case, the embodiments involving the control / regulation of the "cable winches" are particularly applicable to all existing cable winches.

[0011] The working mechanism includes a first measuring device and a control unit. The first measuring device can detect closure variables, and the control unit connected to the first measuring device can actuate or control the cable winch (or, in the case of a mechanical grab, at least one of the cable winches). The control unit can control or adjust the cable winch to raise / lower and close / open the grab in a desired manner.

[0012] Unless otherwise stated, references to the control of cable winches (singular form) below shall include situations where the working machinery has multiple cable winches, at least one of which (particularly a traction winch) is controlled. In the case of multiple cable winches, the control device is preferably capable of controlling all cable winches, and these cable winches are controlled, in particular, independently of each other.

[0013] The closed variable is characterized by the closing force acting during the closing of the grab shovel during the excavation process. The closed variable can be a force acting on the cable, a torque acting on the cable winch, or other derived variables such as motor current or hydraulic pressure. The closed variable measures the degree of resistance experienced by the grab shovel during closure, i.e., the magnitude of the closing force during the closure process.

[0014] According to the invention, the control unit is configured to control or adjust the cable winch based on a set value during the excavation process, such that the grab is held with a predetermined residual tension.

[0015] To optimize the closure process while ensuring that the closure force does not become excessive and the digging process is effectively executed, according to the present invention, the control unit is configured to change a setpoint based on detected closure variables during the digging process, i.e., during the closure process of the grab shovel. The residual tension therefore does not remain constant, but adapts, under certain conditions, based on the currently occurring closure force as manifested by the detected closure variables.

[0016] In one possible implementation, the first measuring device includes a force sensor to detect closure variables. This force sensor can be designed, for example, as a dynamometer that detects cable forces detected during grab closure, such as forces in the closing cable in a mechanical grab configuration. The force sensor may, for example, include one or more strain gauges.

[0017] Alternatively or additionally, the first measuring device may include a torque sensor to detect the closing variable. This torque sensor may, for example, detect the torque acting on a cable winch during grab closure, such as the closed cable winch in a mechanical grab configuration. For example, the torque sensor may include one or more strain gauges.

[0018] As an alternative or supplement to the closure variable that directly depends on the closing force, a closure variable that indirectly depends on the closing force can be detected. For this purpose, the first measuring device may include a pressure sensor for detecting hydraulic pressure in a hydraulic system, such as in a hydraulic grab system that drives at least one hydraulic closing cylinder, or in a mechanical grab system that drives a hydraulic winch motor. In the latter case, it may involve a winch motor for closing a cable winch.

[0019] The detection of hydraulic pressure is based on the understanding that an increase in closing force manifests as an increase in pressure in the hydraulic system of the actuator used to close the grab shovel, thus allowing the detected pressure to be used as a closing variable.

[0020] If an electric motor is used instead of a hydraulic winch motor in a mechanical grab system, the motor current of the electric winch motor can be used as a closed variable to replace the hydraulic pressure.

[0021] Combinations of the aforementioned sensors can also be used to achieve more accurate detection of closed variables. Therefore, for example, direct measurement of closing force or closing torque can be combined with indirect detection derived from pressure or motor current measurements.

[0022] In another possible embodiment, the closed variable is specified as force, torque, pressure, or current intensity. If the closed variable is compared to a corresponding limit value by the control unit, for example, to activate or deactivate an adaptation mode or auxiliary mode, the corresponding limit values ​​have the same unit.

[0023] In another possible embodiment, the working machinery includes a second measuring device by means of which an actual value representing the current remaining tension is detected, and the grab is held in place by means of this actual value. A control unit is connected to the second measuring device and obtains the detected actual value from it. The control unit is configured to compare the actual value with a set value as described above and, based on the comparison, control or adjust at least one cable winch to adjust the desired remaining tension.

[0024] In another possible embodiment, the second measuring device includes a force sensor and / or a torque sensor. The possible designs described above regarding the first measuring device also apply to the force sensor and / or torque sensor of the second measuring device.

[0025] Alternatively or additionally, the second measuring mechanism may include a pressure sensor for detecting hydraulic pressure in the hydraulic system driving the hydraulic winch motor, or, in the case of an electric winch motor, a sensor for detecting the motor current of the winch motor to detect the actual value. This is particularly relevant to winch motors for cable winches. The possible designs described above with respect to the first measuring device are also applicable to pressure detection or motor current detection by means of the second measuring device.

[0026] In another possible embodiment, the setpoint is specified as a force setpoint, specifically a setpoint for the residual tension. For this purpose, for example, a force measurement of the actual value of the residual tension can be performed directly. Here, the control unit specifically adjusts the residual tension to the setpoint. Alternatively, the actual value can be derived or calculated from measurements of torque and / or hydraulic pressure or motor current. Alternatively, the setpoint can be a torque setpoint, a pressure setpoint, or a current intensity setpoint.

[0027] In a preferred design, the setpoint is a pressure setpoint, wherein the actual value is determined by pressure measurements in the hydraulic system of the hydraulic winch motor.

[0028] In another possible embodiment, the control unit is configured to increase the remaining tension by controlling or adjusting the cable winch, particularly the traction winch, when a detected increase in the closure variable is detected. If the closure force increases and thus the closure variable increases during the excavation process or grab closure, the increase in the remaining tension leads to a decrease in the closure force. This reduces the load on the grab shovel or the drive responsible for the closure process.

[0029] Preferably, the control unit is further configured to reduce the residual tension when the detected closure variable decreases. The residual tension can also be reduced if the closure force and thus the closure variable decrease again after the residual tension increases or due to changed soil properties, in order to ensure an effective excavation process.

[0030] In another possible embodiment, the control unit is configured to adapt the remaining tension by controlling or adjusting the cable winch according to a functional relationship based on the detected closed variable. Specifically, the setpoint is changed according to the functional relationship, thereby adjusting the remaining tension accordingly. Preferably, this is a linear relationship (i.e., the remaining tension changes proportionally to the closed variable, i.e., increases or decreases if necessary).

[0031] Preferably, the control unit is configured to keep the remaining tension below the upper limit value. This prevents excessive load on the cable winch (especially the traction winch) responsible for holding the grab. The upper limit value is particularly less than the maximum tension of the cable winch.

[0032] The upper limit value can correspond to a portion of the maximum tension of the cable winch (e.g., 40%, 50%, or 60%). The upper limit value can be stored in the control unit or, in particular, can be set via an input unit connected to the control unit.

[0033] Preferably, a lower limit value is also present, wherein the set value is functionally, particularly linearly, matched according to a closed-loop variable between the lower limit value and the upper limit value. The lower limit value may correspond to a portion of the maximum tension of the cable winch (e.g., 20%, 25%, or 30%). The lower limit value may be stored fixedly in the control unit, or in particular, set via an input unit connected to the control unit.

[0034] In another possible embodiment, the control unit is configured to perform residual tension adaptation depending on the closing variable only in adaptation mode or auxiliary mode, wherein the auxiliary mode is preferably activated and deactivated via an input in an input unit connected to the control unit. The input unit may be located in the operator's cab of the machine tool and may be designed, for example, as a touchscreen display. Thus, the operator of the machine tool can activate or deactivate residual tension adaptation depending on the closing force as needed.

[0035] It can also be specified that, under certain preconditions (such as variables detected by the excavation process or working machinery reaching certain limits), such as when a particularly hard foundation is identified, the residual tension adaptation (i.e., auxiliary mode) depending on the closing force is automatically activated or deactivated.

[0036] In another possible embodiment, the control unit is configured to change the remaining tension only when the detected closed variable is above the lower limit of the closed variable and / or below the upper limit of the closed variable. Preferably, the adaptation range is defined by the lower limit and the upper limit of the closed variable, wherein preferably, no adjustment of a specific remaining tension is made below this range, or an adjustment of a constant remaining tension (e.g., 10% of the maximum tension of the cable winch) is made, and / or, wherein preferably, an adjustment of a constant remaining tension is made above this range, which may, for example, correspond to the upper limit of force (e.g., 40%, 50%, or 60% of the maximum tension of the cable winch).

[0037] The set values ​​are preferably matched between the lower limit value and the upper limit value of the closed variable according to the functional relationship, especially according to the linear function, so that the remaining tension also depends on the closed variable and is adjusted according to the functional relationship.

[0038] The lower limit value and / or upper limit value of a closed variable can be stored in the control unit in a fixed manner, or can be adjusted by an input unit connected to the control unit.

[0039] In another possible embodiment, the grab is specified as a hydraulic grab, and the grab shovel is capable of being opened and closed by at least one, preferably two, hydraulic cylinders (closing cylinders). The grab is held on the boom or mast of the working machinery by a tether, and the remaining tension is adjusted by the corresponding control / regulation of a tether winch equipped with the tether.

[0040] Alternatively, the grab can be a mechanical grab, wherein the grab is suspended from the boom or mast of the working machine by a traction cable and a closing cable, wherein the traction cable is mounted on a traction winch for adjusting or moving the grab, in particular substantially vertically, and the closing cable is mounted on a closing cable winch in a retractable and deployable manner for actuating, i.e. opening and closing, the grab shovel.

[0041] In mechanical grab bucket systems, two cables can be used to adjust the grab bucket and / or open or close the grab shovel. Therefore, to adjust (raise or lower) the grab bucket, both cables are wound up or unwound together. Furthermore, opening the grab shovel can be achieved either by unwinding the closing cable, by winding up the traction cable, or a combination thereof. Similarly, closing the grab shovel can be achieved either by winding up the closing cable, by unwinding the traction cable, or a combination thereof. For actuating the grab shovel, a closing cable is preferably used, which is specifically guided by the cable traction mechanism of the diaphragm wall grab shovel to achieve a high closing force.

[0042] In the mechanical grab bucket scheme, the control unit is configured to control or adjust at least one cable winch, preferably two cable winches (i.e., the traction winch and the closing cable winch) according to a set value, so that the grab bucket is held with a predetermined residual tension.

[0043] In another possible embodiment, the working machine includes an output unit, particularly a display arranged in the operator's cab, on which the current remaining tension and / or closed-loop variable and / or setpoint can be displayed digitally and / or graphically. Alternatively or additionally, the functional relationships described above can be shown graphically. Alternatively or additionally, the lower limit values ​​of force and / or the upper limit values ​​of force and / or the lower limit values ​​of closed-loop variable and / or the upper limit values ​​of closed-loop variable described above can be shown digitally and / or graphically. Thus, the operator of the working machine can quickly and intuitively obtain the current situation during the excavation process. The output unit can also be an input unit or connected to an input unit through which one or more of the above-mentioned parameters can be adjusted.

[0044] Furthermore, the present invention relates to a method for performing a digging process by means of a working machine according to the invention. This method has the same characteristics, features, and advantages as those already described with respect to the working machine according to the invention. Therefore, repeated descriptions are omitted. In particular, the working machine used for the digging process within the scope of the method according to the invention can be designed in any combination of any of the foregoing embodiments.

[0045] In this method, a closure variable is detected, representing the closing force acting when the grab bucket is closed during the excavation process. During the excavation process, the cable winch (particularly the traction winch) is controlled or adjusted according to a setpoint so that the grab bucket is held with a predetermined residual tension. The setpoint changes based on the detected closure variable during the excavation process. Specifically, if the closure variable increases during grab bucket closure, the setpoint and the adjusted residual tension increase. Preferably, when the closure variable decreases, the setpoint and the adjusted residual tension also decrease again.

[0046] In one possible embodiment of the method, it is specified that when the value is above the lower limit of the closed variable and / or below the upper limit of the closed variable, the set value is automatically changed according to the detected closed variable based on the functional relationship, particularly the linear relationship.

[0047] In another possible embodiment, the setpoint and the resulting residual tension are specified to automatically increase when the detected closure variable increases and preferably to automatically decrease when the closure force decreases, wherein the increase or decrease of the setpoint or residual tension is specifically performed automatically only in the active auxiliary mode.

[0048] The steps are specifically performed by the control unit of the machine tool described above.

[0049] Furthermore, the present invention also relates to a computer program product comprising instructions that, when executed by a control unit of a machine tool according to the invention, perform steps of the method according to the invention (of the control unit, i.e., automatically executable). Attached Figure Description

[0050] Other features, details, and advantages of the invention will become apparent from the embodiments described below with reference to the accompanying drawings. The drawings show:

[0051] Figure 1a A side view of a first embodiment of a working machine with a mechanical grab according to the present invention is shown;

[0052] Figure 1b A schematic side view of a hydraulic grab bucket according to a second embodiment of the working machine according to the present invention is shown;

[0053] Figure 2 An example showing the functional relationship between the set residual tension and the closed variable; and

[0054] Figure 3 An example is shown on the display unit of the working machine. Detailed Implementation

[0055] exist Figure 1a A side view of a first embodiment of the working machine 10 according to the invention is shown, wherein the foundation and the bottom trench established in the foundation can be seen in a schematic cross-sectional view. The bottom trench may be filled with wall-protecting mud. The working machine 10 of the embodiment shown here is a cable excavator 10 having a chassis 13 including a tracked walking mechanism, a superstructure 14 rotatably supported on the chassis, and a cantilever 15 pivotally fastened to the superstructure 14. The superstructure 14 may have a cab 16.

[0056] The underground continuous wall grab bucket 20 of the machinery is suspended on the cantilever 15 by two steel cables, which are guided to the superstructure 14 via the cantilever 15, particularly via rollers on the cantilever head; the traction cable 21 is coiled and unfolded and mounted on the traction winch 11 fastened to the superstructure 14; the closing cable 22 is coiled and unfolded and mounted on the closing cable winch 12 also arranged on the superstructure 14.

[0057] The diaphragm wall grab bucket 20 includes a grab bucket frame with two grab bucket shovels 24 pivotally mounted at its lower end. These shovels 24 can be opened and closed by actuating a closing cable 22 (or a closing cable winch 12). The grab bucket shovels 24 can be articulated to the grab bucket carriage via struts. The closing cable 22 is preferably decelerated within the grab bucket 20 via a pulley block or cable system to obtain a greater closing force, and is fastened at one end to the grab bucket carriage of the diaphragm wall grab bucket 20. The cable 21 is, in particular, directly (i.e., without a cable system) fixed to the grab bucket carriage.

[0058] The diaphragm wall grab 20 is particularly free-suspension on the cantilever 15, so that all movements (the raising, lowering, opening / closing of the grab shovel 24 and, in particular, the rotation of the grab 20 about the vertical axis) are preferably achieved only by correspondingly actuating the traction winch 11 and the closing cable winch 12.

[0059] The dynamic residual tension adjustment according to the present invention can be applied not only to the underground continuous wall grab bucket 20 of this machine, but also to different types of grab buckets. The following description is not based on... Figure 1a The exact design scheme of the working machine 10.

[0060] The working machine 10 has a control unit through which winches 11 and 12 can be controlled. Furthermore, the working machine has a first measuring device with at least one sensor for detecting a closing variable, representing the closing force acting when the grab closes. It is conceivable that the closing force can be detected directly, for example, by measuring the cable force in the closing cable 22, or by detecting an indirect variable dependent on the closing force, such as torque. Preferably, winches 11 and 12 have hydraulic winch motors powered by corresponding hydraulic systems, and the hydraulic pressure in the hydraulic systems dependent on the closing force is detected as a closing variable. Specifically, the hydraulic pressure present on the winch motor of the closing cable winch 12 can be detected.

[0061] The control unit is specifically designed to adjust the winches 11 and 12 (particularly the cable winch 11) to generate a desired residual tension, which is used to hold the grab bucket 20. Adjustment is made according to a setpoint, which can be a residual tension setpoint. The residual tension is then adapted to a defined closing force by changing the setpoint based on detected closure variables.

[0062] The working machine 10 specifically includes a second measuring device with at least one sensor for detecting an actual value representing the current remaining tension, which is compared with a set value. The remaining tension can also be measured directly, for example, by measuring the tension in the cable 21. Preferably, the hydraulic pressure in the hydraulic system is detected, particularly the hydraulic pressure present on the winch motor of the cable winch 21.

[0063] exist Figure 1b The image schematically illustrates a second embodiment of the grab 20' of the working machine according to the present invention, wherein, with Figure 1a Unlike other implementations, this is a hydraulic diaphragm wall grab bucket.

[0064] exist Figure 2 The diagram illustrates an example of how residual tension can be adapted to a closed variable. In this case, the closed variable, such as the hydraulic pressure detected by a hydraulic pressure sensor, is plotted on the x-axis as a closed variable representing the current closed force, and the setpoint for adjusting the residual tension is plotted on the y-axis.

[0065] The control unit can define a lower limit value x1 and an upper limit value x2 for the closed variable. Below the lower limit value x1, a constant value can be set for the setpoint (specifically, the remaining tension corresponding to a specific portion (e.g., 10%) of the maximum winch tension, where other values ​​are of course conceivable). In this example, the setpoint is adapted based on a linear relationship between the lower limit value x1 and the upper limit value x2, and thus the remaining tension is adapted accordingly. The higher the closed variable and the higher the closing force, the higher the setpoint to which the remaining tension is adjusted. Above the upper limit value x2, the setpoint remains consistently constant.

[0066] The setpoints, adjusted to the lower limit x1 and upper limit x2 of the closed variable respectively, are referred to herein as y1 and y2. Alternatively, y1 and y2 may represent the residual tension adjusted at x1 and x2. These values ​​may correspond to the force limit values ​​of the residual tension stored in the control unit, which correspond to a specific portion of the maximum winch tension (e.g., 25% and 50%, where other values ​​are of course conceivable).

[0067] exist Figure 3 The diagram illustrates a specific embodiment for dynamic residual tension adaptation, showing an example of relevant variables displayed on a display unit in the cab 16. Other values ​​or display possibilities are also conceivable. Here, the lower limit value x1 and the upper limit value x2 of the closed variable are adjusted to 100 bar and 250 bar respectively (the closed variable here is the hydraulic pressure detected as "grab closure pressure"). Linear adaptation of the residual tension is performed between the upper and lower limit values, which are adjusted to 25% and 50% of the maximum winch tension, respectively. Below the lower limit value x1, the residual tension is set to 10% of the maximum winch tension.

[0068] During the closing process of the grab bucket 24, if the grab bucket closing pressure is within the adjusted pressure range of x1 and x2 (these pressures can be stored in the control unit or set by the operator via the input unit if necessary), the remaining pull force increases by a percentage of the adjusted values ​​of the maximum winch pull y1 and y2 (these values ​​can also be stored in the control unit or set via the input unit). This reduces the force acting on the grab bucket shovel 24. If the grab bucket closing pressure decreases again, for example due to the shovel geometry or soil characteristics, the remaining pull force decreases proportionally again to ensure optimal digging action. This ensures a continuous and optimal or efficient closing process, which improves performance and ease of operation.

[0069] The display unit can also be an input unit (e.g., a touch display). Here, it can be one or more operational elements for performing input. For example, in Figure 3 The embodiment shows an operating element 32 for activating / deactivating the dynamic residual tension adapter. Thus, the operator can manually turn the auxiliary system on or off as needed.

[0070] The constant residual tension below the limit value x1 under closed variable conditions can be adjusted by a potentiometer (Poti).

[0071] The values ​​of x1 and x2 and / or y1 and y2 can be directly adjusted through the input / output unit.

[0072] List of reference numerals in the attached diagram:

[0073] 1 Bottom groove

[0074] 10. Working machinery

[0075] 11. Cable winch

[0076] 12 Closed cable winch

[0077] 13. Base frame

[0078] 14. Superstructure

[0079] 15 cantilever

[0080] 16. Driver's cab

[0081] 20 Grab Buckets

[0082] 20' grab bucket (hydraulic grab bucket)

[0083] 21. Towing

[0084] 22 Closed cable

[0085] 24 Grab bucket shovel

[0086] 26 Hydraulic closing cylinder

[0087] 30. Functional relationship between setpoint and closed variable

[0088] 32 Operating elements.

Claims

1. A working machine (10), in particular a cable excavator or a special deep foundation construction device, comprising: Gripper (20), in particular diaphragm wall gripper, having at least two gripper blades (24) which can be opened and closed, which are suspended by means of a cable (21) on a working machine (10); a cable winch (11) on which the cable is mounted in a windable and unwindable manner in order to move the gripper (20); a first measuring device by means of which a closure variable can be detected, which represents a closure force acting when the gripper blades are closed during a digging process; and a control unit connected to the first measuring device, by means of which the cable winch (11) can be actuated, characterized in that the control unit is set up, during a digging process, to - control or regulate the cable winch (11) in accordance with a set value, so that the gripper (20) is held with a predetermined residual tension, and - change the set value in accordance with the detected closure variable.

2. The working machine (10) according to claim 1, wherein the first measuring device comprises a force sensor and / or a torque sensor, and / or wherein the first measuring device comprises a pressure sensor for detecting the hydraulic pressure in a hydraulic system driving a hydraulic winch motor or a hydraulic cylinder (26) or a sensor for detecting the motor current of an electric winch motor, in order to detect the closure variable.

3. The working machine (10) according to claim 1 or 2, wherein The closure variable is a force, a torque, a pressure or a current intensity.

4. The working machine (10) according to any one of the preceding claims, comprising second measuring means by means of which an actual value representative of the current residual pulling force can be detected, wherein, The control unit is set up to compare the actual value with the set value and to control or regulate the cable winch (11) in accordance with the comparison.

5. The working machine (10) according to the preceding claim, wherein the second measuring device comprises a force sensor and / or a torque sensor, and / or wherein the second measuring device comprises a pressure sensor for detecting the hydraulic pressure in a hydraulic system driving a hydraulic winch motor or a sensor for detecting the motor current of an electric winch motor, in order to detect the actual value.

6. The working machine (10) according to any one of the preceding claims, wherein The set value is a force set value, a torque set value, a pressure set value or a current intensity set value.

7. A working machine (10) according to any one of the preceding claims, wherein The control unit is set up to increase the residual tension by controlling or regulating the cable winch (11) when the detected closure variable increases, wherein the control unit is preferably also set up to decrease the residual tension again when the detected closure variable decreases.

8. A working machine (10) according to any one of the preceding claims, wherein The control unit is set up to adapt the residual tension by controlling or regulating the cable winch (11) in accordance with a functional relationship, in particular a linear relationship (30), which depends on the detected closure variable, wherein the control unit is preferably set up to keep the residual tension below an upper force limit value (y2), which is in particular smaller than the maximum tension of the cable winch (11).

9. A working machine (10) according to any one of the preceding claims, wherein The control unit is set up to perform the adaptation of the residual tension depending on the closure variable only in an assistance mode, wherein the assistance mode can preferably be activated and deactivated by an input in an input unit connected to the control unit.

10. A working machine (10) according to any one of the preceding claims, wherein The control unit is configured to change the residual tension in dependence on the detected closure variable only if the detected closure variable is above a lower closure variable limit value (x1) and / or below an upper closure variable limit value (x2), wherein the lower closure variable limit value (x1) and / or the upper closure variable limit value (x2) are preferably fixedly stored in the control unit or can be set by means of an input unit connected to the control unit.

11. The working machine (10) according to any one of the preceding claims, wherein the grab (20) is a hydraulic grab and the grab blade (24) can be opened and closed by means of at least one hydraulic cylinder (26), or wherein the grab (20) is a mechanical grab which is suspended on a jib (15) or a mast of the working machine (10) by means of a lanyard (21) and a closure cable (22), wherein the lanyard (21) is mounted on a lanyard winch (11) for adjusting the grab (20) in particular substantially vertically and the closure cable (22) is mounted on a closure cable winch (12) in a way that it can be wound up and unwound for actuating the grab blade (24), wherein the control unit is configured to control or adjust at least the lanyard winch (11), preferably both winches (11, 12), in dependence on the set value such that the grab (20) is held with a predetermined residual tension.

12. A method of carrying out a digging process by means of a working machine (10) according to any one of the preceding claims, wherein a closure variable is detected, which represents a closure force acting when the grab blade (24) is closed during the digging process, wherein the cable winch (11) is controlled or adjusted in dependence on a set value during the digging process such that the grab blade (20) is held with a predetermined residual tension, wherein the set value is changed, in particular increased, in dependence on the detected closure variable during the digging process.

13. The method of claim 12, wherein, The set value is changed in dependence on the detected closure variable automatically according to a functional relationship, in particular a linear relationship (30), above a lower closure variable limit value (x1) and / or below an upper closure variable limit value (x2).

14. The method of any one of claims 12-13, wherein, The residual tension is increased automatically when the detected closure variable increases and is preferably decreased automatically when the closure force decreases, wherein the increase / decrease of the residual tension is in particular only carried out automatically in an activated assistance mode.

15. A computer program product comprising instructions for carrying out the steps of the method according to any one of claims 12 to 14 when the program is executed by a control unit of a working machine (10) according to any one of claims 1 to 11.

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