Device and method for increasing the operational safety of a felling head

Abstract

The invention relates to a device and a method for harvesting timber using a hydraulically controlled felling head (1) which comprises a gripper and saw unit, wherein the gripper and saw unit has two pivotable gripper arms (4) for harvested material (2) and a cutting element (6) for separating the harvested material (2), wherein the gripper arms (4) can be pivoted into an open state by applying pressure to a first hydraulic line (12a), and the gripper arms (4) can be pivoted into a closed state by applying pressure to a second hydraulic line (12b). According to the invention, the felling head (1) is provided with an opening width sensor (19), and a pressure sensor (15) is arranged in the second hydraulic line (12b), wherein the opening width sensor (19) and the pressure sensor (15) are connected to a controller (13) which is designed to detect a closed state by the pressure (p) measured by the pressure sensor (15) exceeding a predetermined lower limit value (Gp) and to generate a warning signal when a predetermined upper limit value (GW) of the opening width (W) is simultaneously detected in the closed state.

Description

[0001] Device and method for increasing the operational safety of a falling head

[0002] The invention relates to a device for harvesting timber with a hydraulically controlled felling head that can be attached to the boom arm of a vehicle and comprises a grapple and saw unit, wherein the grapple and saw unit has at least one hydraulically actuated pair of two pivotable grapple arms for harvested material and a cutting element for cutting through the harvested material, wherein, by pressurizing a first hydraulic line, the grapple arms of the grapple and saw unit can be pivoted into an open state with maximum opening width, and, by pressurizing a second hydraulic line, the grapple arms can be pivoted into a closed state with a minimum opening width dependent on the harvested material, according to the preamble of claim 1.The invention further relates to a method for increasing the operational reliability of a hydraulically controlled felling head, attachable to the boom arm of a vehicle, with a gripper and saw unit for harvested crop, wherein the operation of the felling head provides for pivoting at least one pair of grippers of two hydraulically pivotable gripper arms of the gripper and saw unit into an opening state with maximum opening width by pressurizing a first hydraulic line, as well as pivoting the gripper arms into a closed state with a minimum opening width dependent on the crop, as well as cutting the crop in the closed state of the gripper arms by activating a cutting element of the gripper and saw unit, according to the preamble of claim 5.

[0003] Devices of the aforementioned type are used for timber harvesting. An operator controls a boom arm from the vehicle in such a way that gripper arms, mounted on a grapple and saw unit, grasp the harvested material, such as a tree trunk. Subsequently, a closing pressure is exerted on the gripper arms via a corresponding hydraulic system, using the aforementioned second hydraulic line and a first hydraulic cylinder. The gripper arms then clamp the tree trunk relative to the boom arm in a pincer-like motion. Once the tree trunk is clamped, the cutting element can be pivoted using a second hydraulic cylinder to cut the tree trunk.The cutting element, for example, is designed as a chainsaw and is usually pivotally mounted in a saw housing. It is operated by a hydraulic motor located in the saw housing and can be pivoted out of the saw housing by means of a hydraulically actuated swivel drive to cut through a log held by the grapple arms in an area below the grapple arms. After the log has been cut, the grapple and saw unit can usually be pivoted by means of a tilting device so that the grapple arms are moved from their cutting position, in which they are essentially horizontally oriented and their pivot axes are correspondingly vertical, to a storage position, in which they are essentially vertically oriented and their pivot axes are correspondingly horizontal.The severed tree trunk can subsequently be laid down by appropriate control of the boom arm, whereby the gripper arms are opened via the aforementioned first hydraulic line and a corresponding resetting movement of the first hydraulic cylinder in order to release the severed tree trunk.

[0004] Safe operation of such a device therefore involves opening and securely enclosing a tree trunk with the grapple arms, cutting the trunk, and safely placing the cut trunk. These processes are carried out by an operator using hydraulic systems, which requires appropriate experience. In particular, it must be ensured that the cut tree trunk is held securely enough in the felling head so that it does not slip out of the grapple arms and fall out of the felling head after cutting and during the entire placement process. In practice, this is primarily achieved through visual inspection. However, a reliable assessment of an operating situation can sometimes be difficult, especially when working in the treetops and direct visual contact is impaired.This can lead to situations where the operator appears to have the log securely gripped by the grapple, yet the severed log slips uncontrollably out of the felling head after being cut. This occurs, for example, when there are forks in the trunk or branches within the working area of ​​the felling head. These forks create the impression of a secure hold when the felling head is positioned against the tree and the grapple is closed, but in reality, they do not. These misjudgments repeatedly lead to dangerous situations that jeopardize the operational safety of timber harvesting.Mounting cameras on the felling head has proven to be impractical because the camera's field of view is usually obscured when working in the treetops, and operating the camera also requires a power supply at the felling head as well as power and data lines and displays, for example in a control cabin of the vehicle, the practical implementation of which would be far too complex.

[0005] The aim of the invention is therefore to realize a device and a method for timber harvesting with a hydraulically controlled felling head that improves the operational safety of timber harvesting but hardly increases the technical effort.

[0006] These objectives are achieved by the features of claim 1. Claim 1 relates to a timber harvesting device with a hydraulically controlled felling head that can be attached to the boom arm of a vehicle and comprises a grapple and saw unit, wherein the grapple and saw unit has at least one hydraulically actuated pair of two pivotable grapple arms for harvested material and a cutting element for cutting the harvested material, wherein, by pressurizing a first hydraulic line, the grapple arms of the grapple and saw unit can be pivoted into an open state with maximum opening width, and, by pressurizing a second hydraulic line, the grapple arms can be pivoted into a closed state with a minimum opening width dependent on the harvested material.According to the invention, it is proposed that the felling head is provided with an opening width sensor for the gripper pair for detecting an exceedance of a predetermined upper limit value of a measured quantity correlated with the opening width, and a pressure sensor for measuring the hydraulic pressure is arranged in the second hydraulic line, wherein the opening width sensor and the pressure sensor are connected to a control unit designed to detect a closed state by exceeding a predetermined lower limit value through the pressure measured by the pressure sensor and, upon simultaneous detection of an exceedance of the predetermined upper limit value of the measured quantity correlated with the opening width in the closed state, to generate a first warning signal.

[0007] According to the invention, the felling head is thus equipped with a warning system that automatically detects critical situations during operation and alerts the operator via a warning signal. For the existence of a critical situation, a practical criterion was developed according to the invention using two mathematical boundary conditions. This criterion reliably detects critical situations and is verifiable with minimal technical effort. Firstly, it includes a predetermined upper limit for a measured parameter of the gripper that correlates with the opening width, and secondly, a lower limit for the pressure in the hydraulic system used to close the gripper.The measurement of the gripper arms, correlated with the opening width, indicates how far the gripper is open and can be determined using various measurements, such as the swivel angle of the gripper arms, the distance between the gripper tips, or the stroke of the piston rod of the hydraulic cylinder responsible for closing the gripper arms. Similarly, the measurement correlated with the opening width could be, for example, the swivel angle of at least one of the gripper arms, and the opening width sensor could be designed as a sensor measuring the swivel angle of at least one of the gripper arms, particularly as an inductive sensor. Inductive sensors based on inductive transducers can be designed without a power supply and are therefore well-suited for use on the felling head.One possible implementation involves arranging an inductive sensor as an opening width sensor within the gripper arm housing. When opening or closing, a gripper arm, upon reaching a certain swivel angle, sweeps across a measuring range of the inductive sensor, thereby generating a measurement signal that indicates when a predefined upper limit for the swivel angle is exceeded. In this case, the swivel angle represents the measured variable correlated with the opening width, because the swivel angle of the gripper arms correlates with the gripper's opening width. Alternatively, it is also possible to have the gripper arm generate a measurement signal when it leaves a measuring range of the inductive sensor, thus indicating that a predefined upper limit for the swivel angle, and therefore the opening width, has been exceeded.

[0008] The determination of the upper limit for the gripper's opening width depends on the specific gripper and its application, particularly its size and the length of its gripper arms. The larger the gripper, the higher the absolute value of the upper limit for the gripper's opening width will be chosen, with empirical data also playing a role in the specific selection of the limit. Practical experience shows that practical limits for the measured variable correlating with the opening width are at least 60% of the measured variable correlating with the maximum opening width.

[0009] The lower pressure limit in the hydraulic system used to close the grapple also depends on the specific felling head. The pressure curve in the hydraulic system for closing the grapple arms of a felling head can be simplified as follows: when the corresponding hydraulic line is pressurized, the grapple arms begin to close. This pressure range depends on the size and design of the grapples and is, for example, 30-40 bar, but it is well-defined for the hydraulic cylinders of a grapple and is subsequently referred to as the closing range. As soon as the grapple arms completely enclose a tree trunk, for example, and the opening width of the grapple can hardly be reduced any further, the pressure in the corresponding hydraulic line increases, and the grapple arms exert increasing pressure on the harvested material.In this situation, the gripper arms are closed with a minimum opening width dependent on the type of crop being harvested. This pressure range is subsequently also referred to as the load range. This pressure range also depends on the size of the grippers and is, for example, around 150 bar. As soon as a secure grip appears to be established, the operator activates the cutting element to sever the tree trunk.

[0010] The lower limit for the hydraulic pressure for the criterion according to the invention is based on the closing and load range and is advantageously located above the pressure range required for pivoting the gripper arms and below the pressure range required for securing the harvested crop, i.e., between the closing and load ranges. In the example above, the lower limit for the pressure would thus be in the range of 40–150 bar. Alternatively, the specified lower limit for the pressure measured by the pressure sensor can also be within the pressure range required for securing the harvested crop; in the example above, the specified lower limit for the pressure measured by the pressure sensor would thus be, for example, 150 bar. The pressure measurement is taken in the hydraulic system provided for closing the gripper.It is noted that such a pressure sensor is not provided for in the conventional manner. However, the arrangement of a pressure sensor is technically simple and avoids interference with an existing hydraulic control system. The system according to the invention is therefore also suitable for retrofitting. As an extension of the warning system, it is further proposed that the control system be additionally designed to detect activation of the cutting element and, if the pressure sensor fails to detect that the predetermined lower limit has been exceeded, to generate a second warning signal.The pressure sensor provided according to the invention is thus also used to generate a second warning signal, namely when the hydraulic pressure measured by the pressure sensor in the second hydraulic line falls below the predetermined lower limit. Here and subsequently, the "failure to detect that the predetermined lower limit has been exceeded" and the "detection that the predetermined lower limit has been fallen below" are considered synonymous. The second warning signal indicates a critical operating situation to the operator, in which the grapple does not exert sufficient pressure, but the operator nevertheless activates the cutting element. In this case, there is a risk that the cut log will slip out of the grapple, assuming it is even possible to cut the log at all.Since it takes several seconds from the activation of the cutting element until the actual start of the cutting process, when the cutting element penetrates the crop, the operator still has the opportunity to quickly deactivate the cutting element again at the second warning signal, before the cutting process begins. The objectives mentioned at the outset are also achieved by the features of claim 5.Claim 5 relates to a method for increasing the operational safety of a hydraulically controlled felling head, attachable to the boom arm of a vehicle, with a gripper and saw unit for harvested crop, wherein the operation of the felling head provides for pivoting at least one pair of grippers of two hydraulically pivotable gripper arms of the gripper and saw unit into an opening state with maximum opening width by pressurizing a first hydraulic line, as well as pivoting the gripper arms into a closed state with a minimum opening width dependent on the crop, by pressurizing a second hydraulic line, and cutting the crop fixed by the gripper arms in the closed state by activating a cutting element of the gripper and saw unit.According to the invention, it is proposed that an opening width sensor for the gripper pair is used to detect an exceedance of a predetermined upper limit value of a measured quantity correlated with the opening width, and that the hydraulic pressure in the second hydraulic line is measured using a pressure sensor, wherein the closing state is detected when a predetermined lower limit value for the pressure measured by the pressure sensor is exceeded, and a first warning signal is generated when an exceedance of the predetermined upper limit value of the measured quantity correlated with the opening width is detected in the closed state.

[0011] As already mentioned, the specified upper limit of the measured variable correlating with the opening width is preferably at least 60% of the measured variable correlating with the maximum opening width. The specified lower limit for the pressure measured by the pressure sensor is preferably above the pressure range required for pivoting the gripper arms and below the pressure range required for securing the crop. In the example above, the specified lower limit for the pressure measured by the pressure sensor would thus be in the range of 40–150 bar. Alternatively, the specified lower limit for the pressure measured by the pressure sensor can also be within the pressure range required for securing the crop. In the example above, the specified lower limit for the pressure measured by the pressure sensor would, for example, be approximately 150 bar.

[0012] The warning signal can be, for example, a visual warning signal in the form of a warning light or similar device in the vehicle's control panel. Alternatively, the warning signal can be an audible or haptic warning signal, such as a vibration of a hydraulic control element. It can also be provided that, in addition to the warning signal, operating functions of the felling head are disabled. For example, activation of the cutting element can be disabled in addition to the warning signal. The cutting element cannot be activated until the grapple is opened and repositioned on the crop. When the grapple is opened, the corresponding second hydraulic line is depressurized, causing the measured pressure to fall below the predetermined lower limit value measured by the pressure sensor, and thus one of the boundary conditions for the criterion according to the invention is no longer met.The warning signal thus goes out and the blocking of operating functions, such as the blocking of activation of the cutting element, is lifted.

[0013] Furthermore, as already described, it can be provided that activation of the cutting element is detected and, if the pressure measured by the pressure sensor fails to detect that the predefined lower limit has been exceeded, a second warning signal is generated. This second warning signal is generated independently of the opening width of the gripper and, like the first warning signal, can be implemented, for example, as a visual warning signal in the form of a warning light or similar in a control panel of the vehicle, or as an acoustic or haptic warning signal.

[0014] The invention will be explained in more detail below with reference to exemplary embodiments and the accompanying figures. These figures show the

[0015] Fig. 1 shows a schematic view of a vehicle with a felling head according to the invention, comprising a gripper and saw unit in the cutting position.

[0016] Fig. 2 shows a schematic view of a vehicle with a felling head according to the invention, comprising a gripper and saw unit in the deposit position.

[0017] Fig. 3a shows an enlarged view of the felling head in the cutting position,

[0018] Fig. 3b shows an enlarged view of the felling head in the storage position, Fig. 4a shows a top view of the gripper and saw unit,

[0019] Fig. 4b shows a view of the gripper and saw unit from below, so that the cutting element is visible; Fig. 5 shows a possible embodiment of a hydraulic circuit for a felling head according to the invention; and the

[0020] Fig. 6 is a diagram to illustrate the boundary conditions of the criterion according to the invention.

[0021] Reference is first made to Figures 1 to 4 to explain the general operation of a felling head according to the invention. Figure 1 shows a schematic view of a vehicle 3 with a felling head 1 according to the invention, having a gripper and saw unit in the cutting position, and Figure 2 shows a schematic view of the vehicle 3 with a felling head 1 according to the invention, having a gripper and saw unit in the deposit position.

[0022] The felling head 1 is attached to a boom arm of the vehicle 3, which is controlled by an operator from the vehicle 3 such that gripper arms 4 (see Fig. 3) arranged on the grapple and saw unit grasp the harvested material 2, such as a tree trunk. Subsequently, a closing pressure is exerted on the gripper arms 4 via a corresponding hydraulic system through the second hydraulic line 12b and a first hydraulic cylinder 5 (see Fig. 4a), which fix the tree trunk by means of a pincer-like movement. After the tree trunk is fixed, the cutting element 6 (see Fig. 4b) can be pivoted by means of a second hydraulic cylinder 8 so that the tree trunk is cut. The cutting element 6 is designed as a chainsaw and is usually pivotably mounted in a saw housing, being driven by a hydraulic motor 7 (see Fig. 8) arranged in the saw housing.4b) can be put into operation and swung out of the saw box using the second hydraulic cylinder 8 to cut through a log held by the gripper arms 4 in an area below the gripper arms 4. After the log has been cut, the gripper and saw unit can be pivoted using a tilting device 9 (see Fig. 3) so that the gripper arms 4 are moved from their cutting position according to Fig. 3a, in which the gripper arms 4 are essentially horizontally oriented and their gripper pivot axes are correspondingly vertical, to a placement position according to Fig. 3b, in which the gripper arms 4 are essentially vertically oriented and their gripper pivot axes are correspondingly horizontal. The cut log can then be placed down in a controlled manner by appropriately controlling the boom arm, whereby the log is held in the position shown in Fig.The first hydraulic line 12a, visible in Figures 1 and 2, and a corresponding return movement of the first hydraulic cylinder 5 open the gripper arms 4 to release the severed log. Using the tilting device 9, the gripper and saw unit can be moved from its storage position as shown in Figure 3b back to its cutting position as shown in Figure 3a.

[0023] In the following, a possible embodiment of a hydraulic circuit for a felling head according to the invention is explained with reference to Fig. 5. If the grapple is to be opened, the first hydraulic cylinder 5 is actuated by means of the first hydraulic line 12a, and the grapple opens. The grapple and saw unit can then be positioned on the crop 2.

[0024] If the gripper is to be closed, the first hydraulic cylinder 5 is actuated by means of the second hydraulic line 12b, and the gripper closes. The pressure profile in the second hydraulic line 12b for closing the first hydraulic cylinder 5 for the gripper arms 4 is shown in simplified form in Fig. 6, which shows both the time course of pressure p and opening width W. The shown course of the opening width W reflects the course of the measured quantity correlated with the opening width W. When the second hydraulic line 12b is pressurized, the gripper arms 4 initially begin to close, and the opening width W decreases until the gripper arms 4 completely enclose, for example, a tree trunk, and the opening width W of the gripper can hardly be reduced any further. This pressure range is shown in Fig.The closing area S is shown in section 6 and is characterized by the change from a maximum opening width W in the open state to a minimum opening width W in the closed state. The pressure range for pivoting the gripper arms 4 depends on the size of the grippers and is, for example, 30–40 bar.

[0025] As soon as the gripper arms 4 completely enclose the tree trunk and the opening width W of the gripper can hardly be reduced any further, the pressure p in the second hydraulic line 12b increases, and the gripper arms 4 exert increasing pressure on the harvested crop 2. Figure 6 shows a pressure curve in which the pressure p is finally no longer increased once a secure grip appears to have been achieved. This pressure range is shown in Figure 6 as load range L and also depends on the size and design of the grippers. The pressure level shown in Figure 6 in load range L is, for example, 150 bar. The criterion according to the invention now includes, on the one hand, a predetermined upper limit value Gw for a measured variable of the gripper arms that correlates with the opening width W, and on the other hand, a lower limit value G. pfor the pressure in the hydraulic system that is provided for closing the gripper arms 4. The measured variable, which correlates with the opening width W of the gripper arms 4, indicates how far the gripper is open and can be determined via various measured variables, for example, the swivel angle of the gripper arms 4, the distance between the gripper tips, or the stroke of the piston rod of the first hydraulic cylinder 5, which is provided for closing the gripper arms 4. The opening width W is determined by an opening width sensor 19 arranged on the falling head 1 (see Fig. 4a). Fig. 4a shows an opening width sensor 19, which in the illustrated embodiment is designed as an inductive sensor.The inductive sensor is arranged in a housing of the gripper arms 4 such that, when a gripper arm 4 opens, it enters a measuring range of the inductive sensor from a certain swivel angle and thus generates a measurement signal indicating that a predefined upper limit value Gw for the swivel angle has been exceeded. In this case, the swivel angle represents the measured quantity that correlates with the opening width W, because the swivel angle of the gripper arms 4 correlates with the opening width W of the gripper.

[0026] The pressure p is measured via a pressure sensor 15, which is arranged in the hydraulic system responsible for closing the gripper, in the illustrated embodiment therefore in the second hydraulic line 12b (see Fig. 5). The measured values ​​from the opening width sensor 19 and the pressure sensor 15 are transmitted to a controller 13, which is designed to establish a closing state by exceeding a predetermined lower limit value G. pto detect the pressure p measured by pressure sensor 15 and, if the predefined upper limit Gw of the measured variable corresponding to the opening width W in the closed state is simultaneously detected as being exceeded, to generate a warning signal. In the embodiment shown in Fig. 6, the predefined upper limit Gw of the measured variable corresponding to the opening width W was selected as 60% of the measured variable corresponding to the maximum opening width W. For a gripper with a maximum opening width W of, for example, 1200 mm, the upper limit Gw is therefore 720 mm. The predefined lower limit G pIn the embodiment shown in Fig. 6, the pressure p measured by the pressure sensor 15 lies above the pressure range required for pivoting the gripper arms 4 and below the pressure range required for securing the harvested crop 2, i.e., between 40 and 150 bar, for example at 100 bar. The control unit 13 first identifies an exceedance of the predefined lower limit G. pThe system uses the pressure p measured by pressure sensor 15 and, in this case, evaluates the instantaneous value determined by opening width sensor 19 for the measured quantity correlated with the opening width W. If this value falls below the predefined upper limit Gw for the measured quantity correlated with the opening width W, no warning signal is generated, as shown in Fig. 6. The corresponding first warning zone WB1 is shown hatched in Fig. 6. If this value exceeds the predefined upper limit Gw for the measured quantity correlated with the opening width W, i.e., falls within warning zone WB1, the first warning signal is generated. As mentioned, the warning signal can, for example, be implemented as a visual warning signal in the form of a warning light or the like in a control panel of the vehicle 3. It can also be provided that, in addition to the warning signal, operating functions of the falling head 1 are disabled.For example, in addition to the first warning signal, activation of the cutting element 6 can be blocked. The cutting element 6 cannot be activated until the grapple is opened and repositioned on the crop 2. When the grapple is opened, the corresponding second hydraulic line 12b is depressurized, so that the measured pressure p falls below the specified lower limit G. p The pressure p measured by pressure sensor 15 drops, and one of the boundary conditions for the required criterion is therefore no longer met. The warning signal thus goes out, and the block on operating functions, such as the block on activating the cutting element 6, is lifted.

[0027] As soon as a secure grip appears to be established, the cutting element 6 is activated to cut through the log. For this purpose, a first hydraulic valve 11 (see Fig. 5) is provided, which is connected on the inlet side via the connecting line 14 to the second hydraulic line 12b and on the outlet side to the hydraulic motor 7 and the second hydraulic cylinder 8 for the cutting element 6. The first hydraulic valve 11 is designed to direct hydraulic fluid from the second hydraulic line 12b to the hydraulic motor 7 and the second hydraulic cylinder 8 when a threshold value of the inlet pressure is exceeded. The threshold value is selected such that the hydraulic valve 11 only opens when the grapple is completely closed. In this way, the cutting element 6 is also only activated after the grapple has completely closed.After commissioning, the saw is swung out by the hydraulic motor 7 using the second hydraulic cylinder 8. A possible threshold value is, for example, 200 bar. Furthermore, a first accumulator 17 is provided for leakage oil from the hydraulic motor 7, which is connected to the first hydraulic line 12a. This first accumulator 17 collects leakage oil from the hydraulic motor 7 and returns it to the first hydraulic line 12a after the sawing process is complete.

[0028] To prevent the hydraulic motor 7 from running incorrectly when the first hydraulic line 12a is pressurized, a second hydraulic valve 16 is provided, which is connected on the inlet side to the first hydraulic line 12a and on the outlet side to the hydraulic motor 7, wherein the second hydraulic valve 16 is designed to direct hydraulic fluid from the hydraulic motor 7 into the first hydraulic line 12a and to block it in the opposite direction.

[0029] Furthermore, a second accumulator 18 is provided for the hydraulic fluid of the second hydraulic cylinder 8 for the return movement of the second hydraulic cylinder 8. With the aid of the second accumulator 18, the cutting element 6 is thus swung back into place after completion of the cutting process.

[0030] Figure 6 also shows a second warning zone WB2. This second warning zone WB2 is defined by the boundary condition that the hydraulic pressure measured by the pressure sensor 15 in the second hydraulic line 12b is below the specified lower limit value G. p If the cutting element 6 is activated in this pressure range, there is a high probability of a critical operating situation. Therefore, if the cutting element 6 is activated and the exceedance of the predefined lower limit G is not detected, pA second warning signal is generated by the pressure measured by pressure sensor 15. This second warning signal is generated independently of the opening width W of the gripper and, like the first warning signal, can be implemented, for example, as a visual warning signal in the form of a warning light or the like in a control cabin of the vehicle 3, or as an acoustic or haptic warning signal. Since it takes a few seconds from the activation of the cutting element 6 until the actual start of the cutting process, in which the cutting element 6 penetrates the crop 2, the operator still has the opportunity to quickly deactivate the cutting element 6 again before the cutting process begins upon penetration of the crop 2.The invention thus provides a device and a method for harvesting timber with a hydraulically controlled felling head 1, which improve the operational safety of timber harvesting but hardly increase the technical effort.

Claims

Patent claims:

1. Device for timber harvesting with a hydraulically controlled felling head (1) which can be attached to the boom arm of a vehicle (3) and comprises a grapple and saw unit, wherein the grapple and saw unit has at least one hydraulically actuated pair of two pivotable grapple arms (4) for harvested material (2) and a cutting element (6) for cutting the harvested material (2), wherein, by pressurizing a first hydraulic line (12a), the grapple arms (4) of the grapple and saw unit can be pivoted into an open state with maximum opening width (W), and, by pressurizing a second hydraulic line (12b), the grapple arms (4) can be pivoted into a closed state with a minimum opening width (W) dependent on the harvested material, characterized in that the felling head (1) is equipped with an opening width sensor (19) for the Gripper pair for detecting an exceedance of a predefined upper limit (Gw) of a [missing information] The opening width (W) is provided with a measured quantity correlating with the opening width (W), and a pressure sensor (15) for measuring the hydraulic pressure (p) is arranged in the second hydraulic line (12b), wherein the opening width sensor (19) and the pressure sensor (15) are connected to a controller (13) which is designed to establish a closed state by exceeding a predetermined lower limit (G). p ) to detect the pressure (p) measured by the pressure sensor (15) and to generate a first warning signal when simultaneously detecting an exceedance of the specified upper limit value (Gw) of the measured quantity correlated with the opening width (W) in the closed state.

2. Device according to claim 1, characterized in that the measured variable correlating with the opening width (W) is the swivel angle of at least one of the gripper arms (4) and the opening width sensor (19 ) is designed as a sensor measuring the swivel angle of at least one of the gripper arms (4).

3. Device according to claim 1 or 2, characterized in that the opening width sensor (19 ) is designed as an inductive sensor.

4. Device according to one of claims 1 to 3, characterized in that the control unit (13) is additionally designed to detect activation of the cutting element (6) and, in the event of activation of the cutting element (6) and failure to detect that the predetermined lower limit value (G) has been exceeded, p ) to generate a second warning signal by the pressure (p) measured by the pressure sensor (15).

5. Method for increasing the operational safety of a hydraulically controlled felling head (1) attachable to the boom arm of a vehicle (3) with a gripper and saw unit for harvested crop (2), wherein the operation of the felling head (1) provides for pivoting at least one pair of grippers of two hydraulically pivotable gripper arms (4) of the gripper and saw unit into an open state with maximum opening width (W) by pressurizing a first hydraulic line (12a), and for pivoting the gripper arms (4) into a closed state with a minimum opening width (W) dependent on the harvested crop by pressurizing a second hydraulic line (12b), and for cutting the harvested crop (2) fixed by the gripper arms (4) in the closed state by activating a cutting element (6) of the gripper and saw unit, characterized in thatthat, with the aid of an opening width sensor (19) for the gripper pair, an exceedance of a predetermined upper limit (Gw) of a with the, The opening width (W) is detected as a measured quantity correlating with the opening width, and the hydraulic pressure (p) in the second hydraulic line (12b) is measured using a pressure sensor (15), whereby when a predetermined lower limit (G) is exceeded p ) for the pressure measured by the pressure sensor (15) the closing state is detected, and upon simultaneous detection of an exceedance of the specified upper limit (Gw) a first warning signal is generated in the closed state by the measured quantity correlating with the opening width (W).

6. Method according to claim 5, characterized in that the predetermined upper limit (Gw) of the The measurement correlated with the opening width (W) must be at least 60% of the measurement correlated with the maximum opening width (W).

7. Method according to claim 5 or 6, characterized in that the predetermined lower limit (G) p ) for the pressure (p) measured by the pressure sensor (15) is above the pressure range required for pivoting the gripper arms (4) and below the pressure range required for fixing the harvested crop (2).

8. Method according to claim 5 or 6, characterized in that the predetermined lower limit (G) p ) for the pressure (p) measured by the pressure sensor (15) is within the pressure range required to fix the crop (2).

9. Method according to claim 5 or 6, characterized in that the activation of the cutting element (6) is detected and, if the cutting element (6) is activated and the exceedance of the predetermined lower limit value (G) is not detected, p ) a second warning signal is generated by the pressure (p) measured by the pressure sensor (15).

10. Method according to one of claims 5 to 9, characterized in that, in addition to the first or second warning signal, a blocking of operating functions of the falling head (1) takes place.

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