GRIPPER DEVICE AND METHOD FOR OPERATING A GRIPPER DEVICE

Description

[0001] The invention relates to a method for operating a gripper device with a carrier device and a rope gripper arranged thereon, the gripper having a gripper frame which is held on the carrier device by a retaining rope, at least two gripper blades which are pivotably mounted at a lower end of the gripper frame between a closed position and an open position, and an actuating device with an actuating rope for pivoting the gripper blades, wherein an actuating rope is led from the carrier device to the actuating device and the carrier device has a driven first winch for the retaining rope and a driven second winch for the actuating rope, wherein the carrier device has a subcarriage and a supercarriage rotatably mounted thereon about a vertical axis with a boom arm on which the rope gripper is vertically adjustable.wherein, in order to form a slot in the ground in an excavation step, the cable grab with open grab buckets is lowered into the ground by means of the retaining cable, in order to excavate and pick up soil material the grab buckets are closed, the cable grab is pulled out of the ground by means of the retaining cable and / or the actuating cable and pivoted to an emptying position by rotating the superstructure, in which the grab buckets are opened to discharge the picked-up soil material, and subsequently the cable grab is moved back into the ground slot to repeat the excavation step, according to the preamble of claim 1.

[0002] The invention further relates to a gripper device with a carrier device and a rope gripper arranged thereon, the gripper having a gripper frame which is held on the carrier device by a retaining rope, at least two gripper blades which are pivotably mounted at a lower end of the gripper frame between a closed position and an open position, and an actuating device with an actuating rope for pivoting the gripper blades, wherein an actuating rope is led from the carrier device to the actuating device and the carrier device has a driven first winch for the retaining rope and a driven second winch for the actuating rope, wherein the carrier device has a subcarriage and a supercarriage rotatably mounted thereon about a vertical axis with a boom arm on which the rope gripper is vertically adjustable, according to the preamble of claim 9.

[0003] Grab devices are used in specialist foundation engineering to create trenches in the ground. Diaphragm walls can then be constructed within these trenches to support and / or seal excavation pits.

[0004] Grab devices essentially comprise a grab with grab buckets, the grab being suspended from a carrier device, typically a boom crane, by a tether cable. The tether cable allows the grab to be lowered into the ground. By closing the grab buckets, soil material can be excavated and collected in the grab. The grab is then pulled back out of the ground using the tether cable and / or operating cable and swung by the carrier device to a discharge position, where the grab buckets are opened to release the soil material. The grab is then swung back into its working position and inserted into the trench in the ground for another grab operation.

[0005] There are two different types of grippers used on such gripping devices: hydraulic grippers and cable grippers. A so-called hydraulic gripper is known, for example, from EP 3 798 367 A1 and EP 0 533 558 A1. In a hydraulic gripper, the movement for opening and closing the gripper blades is generated by a hydraulic cylinder located on the gripper frame.

[0006] These types of hydraulic grabs are relatively easy to operate and control thanks to the hydraulic system. However, corresponding hydraulic lines are required for the supply and return of hydraulic fluid; these run parallel to the tether cable. The carrier device must be equipped with appropriate hose reels for the hydraulic lines, along with suitable winch drives and a correspondingly designed hydraulic system. This increases the size and cost of the grab device. The hydraulic system also requires additional maintenance.

[0007] In contrast, so-called cable grabs offer a significantly simplified design. Such a cable grab is known, for example, from JP 2001 064993 A and GB 2 126 981 A. In a cable grab, the opening and closing movement of the grab buckets is effected by an actuating cable. The actuating cable runs essentially parallel to the retaining cable from the actuating device of the grab buckets to the carrier machine. By means of a separate winch for the actuating cable, the grab buckets can be opened or closed by unwinding or winding the actuating cable onto the winch.

[0008] With a cable grab, the complex hydraulic lines leading to the grab are eliminated. Only an additional operating cable with a corresponding winch is required. Such an operating cable also requires significantly less maintenance than hydraulic lines and a corresponding hydraulic system.

[0009] However, operating a cable grab is not as simple as operating a hydraulic grab and requires an experienced machine operator. One main reason for this is that the dual arrangement of a non-rotatable cable—namely the holding cable and the operating cable—generates torques in different operating states, causing a certain degree of rotation of the cable grab around its longitudinal axis. Precise rotation of the cable grab is essential to safely move it between the emptying position and a working position, in which the cable grab is inserted into the ground to create a slot.

[0010] A machine operator can rotate the rope gripper around its longitudinal axis by applying specific tensile forces to the holding rope and the operating rope. This requires relatively sensitive operation of the corresponding winches. This demands a certain level of experience and a high degree of concentration from the machine operator during the process. Furthermore, winches are often operated via foot pedals, making such sensitive operation over several hours very strenuous for a machine operator.

[0011] The invention is based on the Task The basis is to specify a method for operating the gripper device and a gripper device in which a simple design of the gripper device is given and simple operation is enabled at the same time.

[0012] The problem is solved, firstly, by a method with the features of claim 1 and, secondly, by a gripper device with the features of claim 9. Preferred embodiments of the invention are specified in the respective dependent claims.

[0013] The method according to the invention is characterized in that a control device is provided with which the rotation of the upper carriage to the emptying position and the opening of the grab buckets to discharge the soil material and / or the rotation of the upper carriage from the emptying position back to the soil slot are automatically controlled. The grab device can also be rotated about its vertical axis.

[0014] A key concept of the invention is to provide a control device that coordinates the operation of a rotary drive for the upper carriage and at least one winch for the operating cable. This enables fast and efficient movement of the cable grab and emptying at the discharge position. The need for time-consuming manual operation by a machine operator, including coordinating the rotation of the upper carriage and / or grab device with the operation of the winch for the operating cable and the winch for the holding cable using the conventional foot pedals, is eliminated. This significantly reduces the workload for the machine operator, both physically and in terms of coordination, especially since a simply constructed cable grab is prone to pendulum motion, i.e., to swinging and / or twisting.The invention allows a rope grab to be operated safely and efficiently even by a less experienced machine operator.

[0015] Alternatively or additionally, according to the invention, the upper carriage can be rotated from the emptying position back to the bottom slot. Thus, the control unit can perform the repetitive movement of the cable grab from the working position at the bottom slot to the emptying position and back completely, almost completely, or at least partially automatically. Initially, a machine operator can perform the first operation manually while the control unit creates a corresponding automatic program using a teach-in procedure. After saving the automatic program, it can be executed repeatedly by the control unit, resulting in a significant reduction in workload for the machine operator.

[0016] A particularly efficient emptying process is achieved according to one embodiment of the invention by having the control device open the grab buckets while the cable grab is still in a pendulum motion due to the rotation of the superstructure. This allows for a dynamic emptying process that eliminates the need for the cable grab to swing freely over the emptying point. This significantly accelerates the work process. The pendulum motion of the cable grab can be caused not only by the rotation of the superstructure but also by the operation of the cable winches. This pendulum motion can include not only oscillation in an approximately horizontal direction but also rotation or torsional oscillation in an approximately vertical direction.The control device allows both the winch for the operating rope and the winch for the holding rope to be controlled in such a way as to counteract any pendulum movement of the rope-suspended rope grab. This improves workplace safety.

[0017] According to a further development of the invention, it is advantageous that the control unit automatically controls the movement of the cable grab into the trench and / or the retraction of the cable grab from the trench. In principle, the extension and retraction of the trench wall grab can also be carried out automatically. The increasing depth of the trench can also be taken into account. Preferably, the machine operator has the option at any time to execute these or other process steps by directly intervening in the control unit. In particular, when inserting the trench wall grab into a trench in the ground, this can be done under direct control by the machine operator.Prior to this, the control unit can execute a program step which leads to a stabilization of the movement of the rope gripper around a vertical axis (twisting) as well as perpendicular to the vertical axis (oscillation) immediately before it enters the created slot.

[0018] Furthermore, it is preferred that the control device is connected to and controls both the first and second winches. This allows for coordinated actuation of the holding and operating cables to limit or completely prevent unwanted rotational and pendulum movements of the cable grab.

[0019] A particularly advantageous operation of the gripper device results from a further development of the invention in the provision of a sensor device with which a pendulum movement of the rope gripper is detected when the superstructure is rotated. The sensor device can be camera-based or comprise other contact or non-contact sensors with which a pendulum movement transverse to the vertical and / or a rotating pendulum movement about a vertical axis is detected. The motion data thus detected can be used by the control unit, in particular for controlling one or both winches, in order to counteract the unwanted or excessive pendulum movement.

[0020] For efficient gripper operation, a further embodiment of the invention provides the advantage that the control device opens the gripper blades at the emptying position while the oscillating rope gripper is still in a deflected position relative to its vertical orientation. This results in an overall acceleration of the process. Furthermore, the targeted emptying of the rope gripper in a deflected position counteracts the pendulum motion, as the resulting reduction in the oscillating mass has a calming effect on the pendulum movement.

[0021] A further efficient process can be achieved by using the control device to guide the oscillating rope grab into the floor slot, thereby dampening the pendulum motion through contact with the floor. Once a certain reduction in the pendulum motion has been achieved, the pendulum motion can be completely stopped by deliberately retracting the rope grab into the floor slot.

[0022] With regard to the gripper device according to the invention, the invention is characterized in that a control device is provided which is designed to automatically control the rotation of the upper carriage to an emptying position and the opening of the gripper buckets to discharge soil material and / or the rotation of the upper carriage from the emptying position back to the soil slot. The advantages described above can be achieved thereby.

[0023] It is particularly preferred in the gripper device according to the invention that it is designed to carry out the previously described method according to the invention.

[0024] Furthermore, in one embodiment of the gripper device according to the invention, it is preferred that a first detection device for detecting a first rope force on the holding rope and a second detection device for detecting a second rope force on the operating rope are provided, and that the control device is connected to the first detection device, the second detection device of the first winch and the second winch and is designed to control the first winch and / or the second winch according to a control program specification, depending on the detected first rope force on the holding rope and the detected second rope force on the operating rope.

[0025] One aspect of the invention is based on the understanding that the torque on a rope gripper about its longitudinal axis depends on the rope forces in the holding rope and the actuating rope. Detection devices are provided to detect the rope force on the holding rope and the rope force on the actuating rope. The respective detected force values ​​can be fed to a control unit, which controls a first winch for the holding rope and a second winch for the actuating rope according to inputs and specifications from the machine operator. Through the control unit, the forces in the holding rope and the actuating rope can be coordinated by appropriately controlling the respective winches (winding / unwinding), so that, in particular, no torque about the longitudinal axis is generated on the rope gripper by the holding rope and the actuating rope when it is in a given or desired rotational position.The control device can also be used to generate a defined variable torque for a desired rotation by appropriately influencing the respective rope forces. This can counteract a pendulum motion.

[0026] A preferred embodiment of the invention consists in the control unit specifying and adjusting a defined ratio between the first cable force in the holding cable and the second cable force in the actuating cable. The control program can take into account identical or different designs of the holding cable and the actuating cable. With preferably identical designs of the holding cable and the actuating cable, but with opposite cable lay patterns, torque compensation can be achieved by setting largely equal tensile forces in the cables. If the cables have different designs with regard to their construction, this can be taken into account and preset accordingly in the control program.When specifying the control program, additional geometric conditions on the rope gripper, such as different attachment points of the ropes on the gripper frame, can also be preset and taken into account.

[0027] Another preferred embodiment of the invention consists in the control device being designed with a compensation mode in which the winches are controlled such that the first rope force on the holding rope and the second rope force on the operating rope are balanced. In particular, the winches can be controlled such that the torques in the operating rope and the holding rope compensate or weaken each other. This stabilizes the rotational position of the rope gripper about its longitudinal axis. Undesired rotation of the rope gripper about its longitudinal axis during operation can thus be largely avoided.

[0028] In particular, according to a further development of the invention, it is advantageous that the control device is designed with a rotation mode in which the winches are controlled in such a way that a targeted rotation of the rope gripper about a vertical longitudinal axis can be generated. Starting from a stable rotational position, a machine operator can effect a desired change in the rotational position. The control device can also be designed such that a value or dimension for a desired rotation is specified by the machine operator via an input device, whereby the control device, according to the program logic, actuates the winches so that the desired changed rotational position is achieved.

[0029] Another preferred embodiment of the invention consists in the control device being designed with a mode for opening and / or closing the grab buckets at a predetermined height. This means that, during opening and / or closing, the two winches can be coordinated so that preferably the lowest point of the grab buckets remains at an unchanged height or a specific change in height is achieved. For example, during closing, it can be controlled whether the teeth or tooth tips of the grab buckets move in a circular path, a straight path, or a defined curve in between. This can be adjusted, in particular, depending on the soil type.

[0030] Preferably, the grab can be suspended freely with closed grab buckets by the operating cable and the retaining cable, with the cable tension in both being approximately equal, for example, approximately + / - 1 ton. Triggered by a control command from the operator, the winch on which the operating cable is wound is automatically actuated in the unwinding direction, either by free fall or by friction. Simultaneously, the winch on which the retaining cable is wound is automatically actuated in the winding direction. This causes a carriage inside the grab body to move upwards and open the grab buckets via the push rods. By controlling the ratio of unwinding the operating cable to winding the retaining cable, vertical movement of the grab body against the surface or ground during opening can be avoided or minimized.Without this control system, the gripper body would otherwise move significantly downwards when the gripper blades open.

[0031] Accordingly, the control device can be designed with a mode for closing the grab buckets. This means that, during opening and / or closing, the two winches can be coordinated so that, preferably, the lowest point of the grab buckets remains at a constant height. Similarly, during closing, it can be controlled whether the teeth or tooth tips of the grab buckets move in a circular path, a straight line, or a curve in between, which is particularly adjustable depending on the soil type.

[0032] Preferably, the grab can be suspended freely with the grab bucket open, suspended by the operating cable and the retaining cable. The cable tension in the retaining cable is almost equal to the total weight of the grab, and the cable tension in the operating cable is in the range of approximately 1 to 2 tons. Triggered by a control command from the operator, the winch on which the operating cable is wound is automatically wound up, and simultaneously the winch on which the retaining cable is wound is automatically unwound, either by free fall or by friction. This causes the carriage inside the grab body to move downwards and close the grab bucket via the push rods.

[0033] By controlling the ratio of winding the closing cable to unwinding the retaining cable, the vertical movement of the gripper body against the surface or ground during closing can be prevented or minimized. Without this control, the gripper body would otherwise move significantly upwards when the gripper blades close. A further preferred embodiment of the invention consists in the control device being designed with a mode for automatically opening and immediately closing the gripper blades.

[0034] Preferably, the grabber can be freely suspended with closed, filled grab bucket on the operating rope and holding rope, wherein the rope force in the operating rope and holding rope is approximately the same, in particular corresponding to approximately + / - 1 t.

[0035] By operating a control element, the opening and closing of the grab buckets is performed automatically in a single sequence. The aim is to complete this in the shortest possible time, as the cable tension in the holding cable is significantly higher than in the operating cable when the grab bucket is open. This can cause the grab to twist around its longitudinal axis. To counteract this twisting, a rotational impulse in the opposite direction can be applied before the automatic opening / closing process, particularly by a targeted, short-term increase in the cable tension in the operating cable.

[0036] Another preferred embodiment of the invention consists in the control device being able to detect the degree of opening of the gripper blades and visualize this for the operator.

[0037] By measuring the ratio of the depth or unwinding length of the retaining cable and the operating cable, it is possible to determine the opening degree of the grab bucket via the machine control system and, in particular, to visualize it for an operator on a screen. This can be done by displaying a numerical value, such as "opening degree 50%", and / or a graphical representation, such as showing the grab buckets with an opening angle or as a bar chart. Without this display, the opening degree of the buckets, and thus the condition of the grab in the slot, is not visually apparent to the operator.

[0038] According to a further development of the invention, it is preferred that at least one third detection device is provided for detecting a rotational position of the rope gripper and / or a change in the rotational position. This can be achieved by an optical detection device, rotary encoder, a gyroscope on the rope gripper, or in another suitable manner. Thus, feedback to the rotational position or the rotation of the gripper can be provided when controlled by the control unit, enabling regulation of the rotational position or the rotation. This allows for particularly precise adjustment of the rotational position of the rope gripper.

[0039] A further improvement in usability is achieved according to another embodiment of the invention by providing at least one additional detection device, in particular for detecting the vertical position of the rope gripper, its distance, and / or its angular position relative to the carrier device. The additional parameters thus detected can be displayed directly to a machine operator and / or processed by the control unit to control the gripper.

[0040] A further advantageous embodiment of the invention consists in the provision of a control panel for a handheld control system for operating the rope grab and / or the winches. The control panel, as an input device, is designed in particular such that a machine operator can input a desired rotation or movement of the rope grab, for example as a numerical value or angular measurement, preferably by means of appropriate operating elements such as a cursor, a rotary knob, switches, or buttons, especially in combination with a display. The machine operator therefore no longer needs to directly input the winches and their rotation. Rather, based on the operator input regarding the position of the grab, the control unit with its program logic controls the machine with the individual motors and actuators in such a way that the desired position is achieved largely without undesired rotations.

[0041] In one embodiment of the invention, it is particularly preferred that the control device is equipped with an automatic program by which the cable grab can be automatically moved to an emptying position and / or to an excavation point. An automatic program can be permanently stored or, for repetitive processes, can be individually defined and saved by a machine operator. In this way, larger movements of the grab can be carried out automatically, in particular a movement to the emptying position and / or back to an excavation point. Such travel paths of the cable grab occur particularly frequently when creating deep trenches in the ground.

[0042] In principle, the individual ropes can be of the same or different designs. According to one embodiment of the invention, it is particularly advantageous that the holding rope on the first winch has a first winding that is opposite to a second winding of the operating rope on the second winch. In particular, the holding rope and the operating rope have opposite lay directions or so-called rope lay patterns. When a tensile force is applied, this results in opposing torques on the ropes. This facilitates the compensation of the torques for stabilizing the position of the rope grab during operation.

[0043] According to a further embodiment of the invention, it is particularly advantageous that a display screen is provided for operating the control device. The display screen can, in particular, be designed as a touchscreen on which at least some of the operating elements for a machine operator are implemented. Furthermore, the display screen can show the position of the rope gripper in various representations to further facilitate operation for the machine operator.

[0044] The grab device can be used for a variety of tasks. One preferred method involves using the cable grab to excavate soil and, in particular, to create a trench in the ground. The cable grab can be designed specifically as a so-called diaphragm wall grab, which can be used to create a trench in the ground for a sealing and / or retaining wall, for example, for excavation shoring.

[0045] The invention is further described below with reference to a preferred embodiment, which is shown schematically in the drawings. In the drawings show: Fig. 1 a perspective view of a gripper device according to the invention; Fig. 2 a front view of the rope gripper of the gripper device. Fig. 1 with closed grab buckets; and Fig. 3 a front view of the rope grab accordingly Fig. 2 with open grab buckets.

[0046] A gripper device 10 according to the invention Fig. 1 The mobile carrier unit 12 has a crawler chassis as its undercarriage 14. A superstructure 16 with an operator's cabin 17 is rotatably mounted on the undercarriage 14 about a vertical axis of rotation. Inside the operator's cabin 17 is a control unit including an input device for a machine operator.

[0047] A boom arm 18 is pivotally mounted on the superstructure 16 about a horizontal axis. A retaining cable 24 is guided on a head 20 of the boom arm 18, which has pulleys. A cable grab 30 with a grab frame 32 and lower grab buckets 34 is attached to the end of the cable. The retaining cable 24 can be actuated to raise and lower the cable grab 30 via a first winch 21 on the carrier unit 12. A second winch 22 is also located on the carrier unit 12 for an actuating cable 44, which is guided via the head 20 to the cable grab 30 for actuating the grab buckets 34 at the lower end of the grab frame 32.

[0048] The functioning of the gripper device 10 according to the invention is described below in connection with the Figures 2 and 3 explained in more detail.

[0049] InIn a central area of ​​the gripper frame 32, an actuating slide 42 of an actuating device 40 for actuating the gripper blades 34 is slidably mounted in a vertical longitudinal direction. The end of the retaining cable 24 is attached to the upper end of the actuating slide 42, so that the cable gripper 30 is held by the actuating slide 42.

[0050] A linkage mechanism 46 with linkage rods 47 is arranged at a lower end of the actuating slide 42. The linkage rods 47 are pivotally connected to the actuating slide 42 on one side and to one of the gripper blades 34 on the other. The gripper blades 34 are themselves pivotally mounted at the lower end of the gripper frame 32 via pivot bearings 35. The gripper blades 34 can be opened and closed by a relative displacement of the actuating slide 42 with respect to the gripper frame 32. A relative displacement of the actuating slide 42 upwards pulls the linkage rods 47 upwards, pivoting the gripper blade 34 about its pivot axes 35 into its open position, which is illustrated in Fig. 3 is shown.

[0051] Below the actuating carriage 42, a pulley system 50 is provided for the actuating cable 44. The pulley system 50 has at least one upper pulley 52, which is rotatably mounted on the actuating carriage 42, and at least one lower pulley 54, which is rotatably mounted on a lower portion of the gripper frame 32. The pulleys 52 and 54 are encircled by the actuating cable 44, which is supplied from above, forming loops 56 or pulleys, with the lower end of the actuating cable 44 being fixedly connected to the gripper frame 32. The actuating carriage 42 is thus adjustably connected or coupled to the gripper frame 32 via the actuating cable 44.

[0052] Starting from the opening position according to Fig. 3By pulling the actuating cable 44 upwards, the second winch 22 pulls the actuating slide 42 downwards relative to the gripper frame 32 via the pulley system 50. During this action, the connecting rods 47 press the gripper blades 34 downwards with an increased closing force, causing the gripper blades 34 to pivot about their pivot bearings 35 into the closed position. Fig. 2 be swerved.

[0053] When used in a slot in the ground, soil material can be gripped and enclosed between the grab buckets 34 by means of a closing force increased compared to the pulling force on the actuating rope 44.

[0054] After the cable grab 30 is pulled out of a slot in the floor and moved to an emptying position, the pulling force on the actuating cable 44 can be reduced. In this way, the grab frame 32 shifts downwards relative to the actuating carriage 42 due to its weight, so that the grab buckets 34 are swung back into their open position via the linkage rods 47, as shown in Fig. 3 is shown.

[0055] The described arrangement is only an example. In principle, other pulley systems with different rope linkages and linkage mechanisms can be chosen to enable comparable grab bucket operation.

[0056] When the grab buckets 34 are filled, the upper carriage 16 is removed from the in Fig. 1The superstructure 16 automatically pivots 90 degrees around its vertical axis to an unloading position. The boom arm 18 can also be adjusted during this process. At the unloading position, the grab buckets 34 open to discharge the soil material, even if the cable grab 30 is still oscillating. The cable grab 30 can also be rotated around its longitudinal axis to align it, for example, with the bed of a truck. The superstructure 16 can then automatically return to the position shown. Fig. 1 be swung back.

[0057] From there, the cable grab 30 is lowered into a slot in the ground to pick up new soil material with its grab buckets 34 open. It is then retracted with its grab buckets 34 closed to its final position. Fig. 1 and another emptying process.

[0058] When the rope gripper 30 is actuated, a coordination of the forces and movements between the holding rope 24 and the actuating rope 44 is necessary in order to control the torques in the individual ropes and thus the torques of the attached rope gripper 30 about its longitudinal axis, in particular due to a so-called lay direction in wound ropes.

[0059] According to the invention, forces in the holding cable 24 and the actuating cable 44 are detected by corresponding sensing devices, which can be arranged, for example, on the cable winches 21, 22 or on the deflection pulleys at the head 20 of the boom arm 18. Depending on the detected cable forces, the winches 21, 22 can be controlled by a control unit, which is preferably located in the operator's cabin 17 on the carrier device 12, in such a way that either the pendulum movement about the longitudinal axis or the rotational position of the cable grab 30 about its longitudinal axis is stabilized, or a targeted rotation desired by the machine operator is achieved. The machine operator can make corresponding inputs to the control unit for desired automatic movement, a compensation mode for position stabilization, or inputs for a desired rotational position of the steep-angle grab 30.Based on this, the control unit of the superstructure 16 can control the boom arm 18 or the winches 21, 22 accordingly to achieve the desired positioning and opening / closing of the rope grab 30. This significantly simplifies and facilitates the control of a simply constructed rope grab 30 for a machine operator.

Claims

1. A method for operating a grab device (10) comprising a carrier device (12) and a cable grab (30) arranged thereon, which comprises - a grab frame (32), which is held by a retaining cable (24) on the carrier device (12), - at least two grab buckets (34), which are mounted on a lower end of the grab frame (32), so as to be able to swivel between a closed position and an open position, and - an actuating device (40) with an actuating cable (44) for swivelling the grab buckets (34), - wherein an actuating cable (44) is guided from the carrier device (12) to the actuating device (40), and - the carrier device (12) has a driven first cable winch (21) for the retaining cable (24) and a driven second cable winch (22) for the actuating cable (44), - wherein the carrier device (12) has an undercarriage (14) and an upper carriage (16), which is mounted thereon for rotation about a upstanding axis having a cantilever arm (18) on which the cable grab (30) is vertically adjustably mounted, wherein - in a removal step, in order to form a trench in the ground, the cable grab (30) is lowered into the ground, - the grab buckets (34) are closed to remove and receive soil material, - the cable grab (30) is pulled out of the ground by the retaining cable (24) and / or the actuating cable (44) and is swiveled into an emptying position, in which the grab buckets (34) are opened to discharge the collected soil material, by rotating the upper carriage (16), and - then the cable grab (30) is moved back into the ground trench to repeat the removal step, characterized in that a control device is provided with which an opening and / or closing of the grab buckets (34) to discharge the soil material are controlled automatically.

2. The method according to claim 1, characterized in that with the control device a rotation of the upper carriage (16) to the emptying position and / or a rotation of the upper carriage (16) from the emptying position back to the ground trench are automatically controlled.

3. The method according to claim 1 or 2, characterized in that by the control device the grab buckets (34) are opened while the cable grab (30) is still in an oscillating movement, as a consequence of the rotation of the upper carriage (16).

4. The method according to claims 3, characterized in that the grab buckets (34) are opened by the control device at the position at a time at which the oscillating cable grab (30) is still in a position deflected out of a vertical position.

5. The method of claim 1, characterized in that the control device is configured with a mode for opening and / or closing the grab buckets (34) at a predetermined height, wherein, during opening and / or closing, the two cable winches (21, 22) are coordinated to one another so that preferably the lowest point of the grab buckets (34) remains at an unchanged height or a specific change in height is achieved.

6. The method of claim 1, characterized in that the cable grab (30) is suspended freely with closed grab buckets (34) on the actuating cable (44) and retaining cable (24).

7. The method according to claim 6, characterized in that, triggered by a control command, the grab buckets are automatically opened by automatically actuating the second winch (22), on which the actuating cable (44) is wound, in the unwinding direction, which takes place either in a free fall or via a friction-based connection.

8. Method according to claim 1, characterized in that, by means of a controlled ratio of the winding-up of the actuating cable (44) and the unwinding of the holding cable (24), a vertical movement of the grab body against the subgrade or the ground during closing is prevented or minimized.

9. A grab device comprising a carrier device (12) and a cable grab (30) arranged thereon, which comprises - a grab frame (32), which is held by a retaining cable (24) on the carrier device (12), - at least two grab buckets (34), which are mounted on a lower end of the grab frame (32), so as to be able to swivel between a closed position and an open position, and - an actuating device (40) with an actuating cable (44) for swivelling the grab buckets (34), - wherein an actuating cable (44) is guided from the carrier device (12) to the actuating device (40), and - the carrier device (12) has a driven first cable winch (21) for the retaining cable (24) and a driven second cable winch (22) for the actuating cable (44), - wherein the carrier device (12) has an undercarriage (14) and an upper carriage (16), which is mounted thereon for rotation about a upstanding axis having a cantilever arm (18) from which the cable grab (30) is vertically adjustably suspended, characterized in that a control device is provided, which is designed to automatically control an opening and / or closing of the grab buckets (34) to discharge soil material at a emptying position.

10. The grab device according to claim 9, characterized in that it is designed to carry out the method according to one of claims 1 to 8.

11. The grab device according to claim 9 or 10, characterized in that - a first detection device for detecting a first cable force on the retaining cable (24) and a second detection device for detecting a second cable force on the actuating cable (44) are provided, - in that the control device is connected to the first detection device, the second detection device, the first cable winch (21) and the second cable winch (22) and is designed to actuate the first cable winch (21) and / or the second cable winch (22) in accordance with a control program specification, depending on the detected first cable force on the retaining cable (24) and the detected second cable force on the actuating cable (44).

12. The grab device according to claim 9 to 11, characterized in that the control device is designed with a compensation mode in which the cable winches (21, 22) are actuated in such a way that the first cable force on the retaining cable (24) and the cable force on the actuating cable (44) are matched to each another, and / or in that the control device is designed with a twist mode in which the cable winches (21, 22) are actuated in such a way that a deliberate twist of the cable grab (30) around a vertical longitudinal axis can be generated.

13. The grab device according to one of claims 9 to 12, characterized in that at least one third detection device for detecting a rotational position of the cable grab (30) and / or a change in the rotational position is provided, and / or in that at least one further detection device is provided, in particular for detecting a vertical position of the cable grab (30), a distance and / or an angular position of the cable grab (30) relative to the carrier device (12).

14. The grab device according to one of claims 9 to 13, characterized in that the retaining cable (24) on the first cable winch (21) has a first lay direction which is opposite to a second lay direction of the actuating cable (44) on the second cable winch (22).

15. The grap device according to claim 9, characterized in that by the control device one is capable of detecting an opening degree of the grab buckets (34) and is visualized to an operator.