Procedure for determining the load center of gravity of a forklift truck and forklift truck for carrying out the procedure

Abstract

Method for determining the load center (L1) of a forklift truck with at least one horizontally cantilevered load handling device (1) for receiving a load (3) and at least one load handling device support (5) on which the load handling device (1) is supported in the horizontal and vertical direction, wherein at least one force (F4) acting directly from the load handling device (1) on the load handling device support (5) in the vertical direction and at least one force (F2, F3) acting directly from the load handling device (1) on the load handling device support (5) in the horizontal direction are measured directly and, given a specific geometry of the load handling device (1) and the load handling device support (5), the position of the load center (L1) of the load (3) is determined therefrom, characterized in thatthat a fork carriage (5) guided on a lifting mast is provided as the load-handling device carrier (5) and a fork tine (1) arranged on the fork carriage with a horizontally cantilevered fork blade (2) for receiving the load (3) and a vertically oriented fork back (4) is provided as the load-handling device (1), wherein the fork tine (1) is supported on the fork carriage (5) via the fork back (4) in the horizontal and vertical directions, and the force (F4) acting vertically downwards from the fork back (4) onto the fork carriage (5) at a support point (6) at the upper end of the fork carriage (5) and the force (F2, F3) acting horizontally from the fork back (4) onto the fork carriage (5) at a support point (6) at the upper end of the fork carriage (5) are measured directly and at a given distance between the support points (7,8) from this the horizontal distance of the load center (L1) of the load (3) from the fork back (4) or from the fork carriage (5) is determined.

Description

[0001] The invention relates to a method for determining the load center of gravity of a forklift truck with at least one horizontally cantilevered load-handling device for receiving a load and at least one load-handling device support on which the load-handling device is supported in the horizontal and vertical direction, wherein at least one force acting directly from the load-handling device on the load-handling device support in the vertical direction and at least one force acting directly from the load-handling device on the load-handling device support in the horizontal direction are measured directly and, given a specific geometry of the load-handling device and the load-handling device support, the position of the load center of gravity of the load is determined from this, as well as a forklift truck for carrying out the method.

[0002] Examples of such industrial trucks include forklifts and reach trucks, which have forks as load-handling devices and a fork carriage as the load-handling device carrier, to which the forks are attached. The fork carriage is vertically adjustable on a lifting mast. It is common practice with such industrial trucks to measure the weight of a load picked up by the load-handling device. A frequently used method for this is to measure the lifting force in the lifting mechanism, for example, by measuring the pressure in a lifting cylinder. However, for calculating the stability of the industrial truck, the location of the center of gravity of the load is also crucial, since the load moment exerted by the load depends on the horizontal distance of the load's center of gravity, for example, from a front axle in the case of a counterbalanced forklift.

[0003] If a forklift truck is equipped with a tilting mast, it is conceivable to determine the center of gravity of the load by additionally measuring forces in the tilting cylinders, provided the load weight is known.

[0004] However, this requires more complex calculations, as the centers of gravity of the lifting mast's mass must also be taken into account, and the geometry, especially the angles and directions of the forces, must be comprehensively considered. For a stationary mast without tilting capability, no statement can be made about the load's center of gravity using this method.

[0005] A commonly used component on forklifts allows the load-handling device, and in particular the forks, to be tilted relative to the mast. The forks are attached to a frame that can rotate around a pivot point at the top and be pivoted at the bottom by tilting cylinders.

[0006] Another built-in device offers the possibility of rotating the fork tines around a longitudinal axis. Here too, the fork tines are attached to a frame that is rotatably mounted and has an upper and lower fork support rail.

[0007] From DE 10 2013 114 940 A1, a method for determining the load center of gravity of a forklift truck is known, in which the fork carriage is rotatably mounted about a pivot axis located at an upper bearing point and is supported against a tilt cylinder at a lower bearing point. The support force is measured indirectly via the pressure in the tilt cylinder. The position of the load center of gravity is determined from the distance between the upper and lower bearing points, the support force measured indirectly via the pressure in the tilt cylinder, and the load weight. However, this method for determining the load center of gravity requires a rotatable fork carriage with a tilt cylinder. It is not applicable to simple, non-tiltable fork carriages.

[0008] DE 40 30 748 A1 discloses a generic method with the features of the preamble of claim 1.

[0009] The present invention is based on the objective of designing a method of the type mentioned at the outset and a forklift truck for carrying out the method in such a way that, with minimal technical effort, the center of gravity of a load picked up can be determined even for forklift trucks without a tilting load-handling device carrier.

[0010] This problem is solved according to the invention by providing a fork carriage guided on a lifting mast as the load-handling device carrier and a fork tine arranged on the fork carriage as the load-handling device, with a horizontally cantilevered fork blade for receiving the load and a vertically oriented fork back, wherein the fork tine is supported on the fork carriage in the horizontal and vertical directions via the fork back.and the force acting vertically downwards from the fork back onto the fork carriage at a support point at the upper end of the fork carriage, as well as the force acting horizontally from the fork back onto the fork carriage at a support point in the upper area and / or at a support point in the lower area of ​​the fork carriage, are measured directly, and, given a specific distance between the support points, the horizontal distance of the load's center of gravity from the fork back or the fork carriage is determined from this.

[0011] In contrast to the method known from DE 10 2013 114 940 A1, neither a tilting load-handling device carrier nor a tilting cylinder is required. Therefore, the invention can also be used with industrial trucks that, for example, have simple standard fork carriages. While in the prior art the support force is measured indirectly by determining the pressure in the tilting cylinder, in the invention the forces acting directly between the load-handling device and the load-handling device carrier are measured directly. This avoids additional sources of error in the measurement and increases the measurement accuracy. Furthermore, the technical effort is reduced compared to pressure measurement in the tilting cylinder.

[0012] From the measured forces, and given the known geometry of the load-bearing device and the load-bearing device support, the position of the load center of gravity of the load being carried can be determined and calculated using simple calculations based on the laws of leverage.

[0013] Furthermore, the measured forces, especially the force in the vertical direction, can be converted into the weight force of the load being lifted. Using the laws of leverage, the measured forces can thus be converted into the weight force of the load acting at its center of gravity. This yields the weight of the load at a given distance.

[0014] Advantageously, the forces are measured using sensors arranged between the load-handling device and the load-handling device support. Strain gauges are preferably used as sensors. Such strain gauges require very little space and can be easily integrated into the load-handling device support so that the corresponding force can be measured across the entire width of the support. This allows the load-handling device to be flexibly positioned on the support.

[0015] According to the invention, a fork carriage guided on a lifting mast serves as the load-handling device carrier. Furthermore, a fork tine, arranged on the fork carriage, serves as the load-handling device. This tine tine has a horizontally cantilevered fork blade for receiving the load and a vertically oriented fork back. The fork tine is supported on the fork carriage via the fork back in both the horizontal and vertical directions. This configuration applies, for example, to forklifts or reach trucks, in which two parallel fork tines with parallel fork blades and fork backs are arranged at a distance from one another. The force acting vertically downwards from the fork back onto the fork carriage at a support point at the upper end is measured directly. Given the empty weight of the fork tine, the weight of the load can be determined and calculated from this force.Additionally, the force acting directly on the fork carriage in a horizontal direction from the fork back at a support point in the upper area and / or a support point in the lower area is measured. These forces correspond to the support forces of the load-handling device and result from the torque that acts on the load-handling device at its center of gravity due to the load's weight. From the measured values ​​of the direct force measurements, the horizontal distance of the load's center of gravity from the fork back or the fork carriage is determined for a given distance between the support points.

[0016] Preferably, the forces are measured at all the aforementioned support points. If a lower measurement accuracy is sufficient, it is also adequate to measure only the vertical force at the upper support point and additionally one of the two horizontal forces, either at the upper or the lower support point. In this case, preferably only the horizontal force at the lower support point is measured in addition to the vertical force. This is also a significant measure for simplifying the measurement method compared to the prior art.

[0017] A further development of the invention provides that the measured values ​​from the force measurements are evaluated in a data processing unit together with values ​​stored in the data processing unit relating to the geometry of the load-handling device and the load-handling device carrier. The load weight and the position of the load's center of gravity are then determined as results. If predefined critical values ​​are exceeded, a warning message is issued and / or the vehicle control system is intervened. In this way, the operator of the industrial truck can be informed and / or supported under critical load conditions. For example, a warning can be issued if the load is positioned too far forward on the load-handling device at a certain load weight, creating a risk of the industrial truck tipping forward. The vehicle control system can also be automatically intervened to, for example,The system can stop the forklift in such critical situations or adjust its speed accordingly. Automatic tilting of the mast or automatic limiting of the lifting height can also occur in such situations. This helps prevent accidents and transport damage.

[0018] The invention further relates to a forklift truck with at least one horizontally cantilevered load-handling device for receiving a load and at least one load-handling device support on which the load-handling device is supported in the horizontal and vertical direction, wherein at least one sensor for directly measuring a force acting directly from the load-handling device on the load-handling device support in the vertical direction and at least one sensor for directly measuring a force acting directly from the load-handling device on the load-handling device support in the horizontal direction are provided, and the sensors are operatively connected to a data processing device which is configured to determine the position of the load's center of gravity from the sensor data and data on the predetermined geometry of the load-handling device and the load-handling device support stored in the data processing device.

[0019] In such a forklift truck, the task is solved by designing the load-handling device carrier as a fork carriage guided on a lifting mast and the load-handling device as a fork tine arranged on the fork carriage with a horizontally cantilevered fork blade for receiving the load and a vertically oriented fork back, wherein the fork tine is supported on the fork carriage in the horizontal and vertical directions via the fork back.and one of the sensors is located at a support point at the upper end of the fork carriage for directly measuring the force acting vertically downwards from the fork back onto the fork carriage, and one of the sensors is located at a support point in the upper area and / or one of the sensors is located at a support point in the lower area of ​​the fork carriage for directly measuring the force acting horizontally from the fork back onto the fork carriage, and the sensors are operatively connected to the data processing unit, which is configured to determine the horizontal distance of the load's center of gravity from the fork back or fork carriage from the sensor data and the distances of the support points stored in the data processing unit.

[0020] The sensors are preferably arranged between the load-handling device and the load-handling device support. Furthermore, the sensors are advantageously designed as strain gauges. They can be easily integrated into the load-handling device support, thus protecting them from damage, e.g., from the load.

[0021] In the industrial truck according to the invention, the load-handling device carrier is designed as a fork carriage guided on a lifting mast. Furthermore, the load-handling device is designed as a fork tine arranged on the fork carriage, with a horizontally cantilevered fork blade for receiving the load and a vertically oriented fork back. The fork tine is supported on the fork carriage in both the horizontal and vertical directions via the fork back. One of the sensors is arranged at a support point at the upper end of the fork carriage for directly measuring the force acting vertically downwards from the fork back onto the fork carriage. Additionally, one of the sensors is arranged at a support point in the upper region and / or one of the sensors at a support point in the lower region of the fork carriage for directly measuring the force acting horizontally from the fork back onto the fork carriage.The sensors are operatively connected to the data processing unit. This unit is configured to determine the horizontal distance of the load's center of gravity from the fork back or fork carriage based on the sensor data and the distances of the support points stored in the data processing unit.

[0022] Preferably, the data processing unit is operatively connected to a display unit and / or a vehicle control unit. Furthermore, the data processing unit is configured to determine the load weight and the position of the load's center of gravity from the sensor data and the stored data, and to issue a warning message to the display unit and / or intervene in the vehicle control system if predefined critical values ​​are exceeded.

[0023] The invention has a whole range of advantages: The invention enables the operator of a forklift truck to be informed and supported in critical situations during operation, particularly when the load is positioned unfavorably on the load-handling attachment. Especially with loads that are not visible, such as those on shelves, or with complex structures or closed transport boxes, the operator can be informed about the position of the load's center of gravity. Corresponding automatic intervention in the vehicle's control system is also possible. This helps prevent accidents and transport damage. Furthermore, the direct force measurement according to the invention is more accurate than, for example, the indirect measurement known from the prior art, which uses pressure in a hydraulic fluid. Additionally, the sensors are protected against mechanical deformation by their mechanical integration into the load-handling attachment carrier.

[0024] Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiment shown in the schematic figures. Here, Fig. 1 a side view of a fork tine with fork carriage and Fig. 2 A detailed view of the fork carrier in cross-section.

[0025] In the Fig. Figure 1 shows the load-handling device 1, designed as a fork tine 1, in a side view. A second, parallel fork tine is not visible in the side view. The fork tine 1 comprises a fork blade 2, on which a load 3 is located, and a fork back 4. The fork back 4 is arranged on a load-handling device support 5, designed as a fork carriage 5. In its upper region, the fork back 4 is shaped so that it hooks around the upper end of the fork carriage 5 and rests on the fork carriage 5 at the support point 6. Laterally, the fork back 4 is supported at the support point 7 in the upper region of the fork carriage 5, while in its lower region it is supported at the support point 8.

[0026] Between the fork back 4 and the fork carriage 5, sensors 9, 10, 11 are attached at the support points 6, 7, 8 according to the invention. The sensors 9, 10, 11 are, for example, each designed as strain gauges.

[0027] The force F4 acting vertically downwards from the fork back 4 is measured directly by sensor 9. This force F4 is composed of the weight force F1 of the load 3 (load weight F1) and the weight force of the empty fork tine 1 (fork empty weight). Since the weight of the empty fork tine 1 (fork empty weight) is known, the weight force F1 of the load 3, i.e., the load weight, can be deduced from the measured force F4 and calculated.

[0028] Sensors 10 and 11 directly measure the horizontally acting forces F2 and F3, which laterally support the fork back 4 against the fork carriage 5. These forces F2 and F3 depend on the load weight and the position of the load's center of gravity L1 of the load 3. As the distance of the load's center of gravity L1 from the fork back 4 or the fork carriage 5 increases, the load moment increases, which in turn increases the lateral support forces F2 and F3.

[0029] From the measured forces F4, F2 and F3, and given known distances between the support points 6, 7 and 8, the distance of the load center L1 from the fork back 4 or from the fork carriage 5 can be determined using the laws of leverage.

[0030] Furthermore, the measured forces F2, F3, and F4, especially the measured force F4 in the vertical direction, can be converted into a weight force F1 of the absorbed force. Using the laws of levers, the measured forces F2, F3, and F4 can thus be converted into a weight force F1 of the absorbed load 3, which acts at the load's center of gravity L1. This yields the load weight F1 at a distance L1 from the load.

[0031] The sensors 9, 10, 11 thus measure the forces F4, F2 and F3 at the support points 6, 7 and 8, which represent the contact points of the fork tine 1 on the fork carriage 5.

[0032] The measurement data are stored in a format that is Fig. The data is evaluated by a data processing unit (not shown) so that if critical values ​​for the load center L1 are exceeded, a warning can be issued and the vehicle control system can be automatically adjusted. For example, if the load weight is too high and the load center L1 is too far from the fork back 4 or the fork carriage 5, the speed of the industrial truck can be automatically limited, the mast can be automatically tilted backward, and / or the lifting height can be limited to prevent the industrial truck from tipping over.

[0033] In the Fig. 2 is a horizontal cross-section through the fork carrier 5 made of Fig. Figure 1 is shown at the height of sensor 11. The reference numerals from the Fig. 1 also for the designation of features that are in the Fig. Figure 2, not shown, is taken from the fork carriage. In this example, the fork carriage 5 has two sensors 11 arranged at its outer ends. A rail 12, connected to the sensors 11, extends across the entire width of the fork carriage 5 to absorb the force exerted by the fork back 4. The rail 12 serves to distribute the force F3 emanating from the fork back 4 evenly to the sensors 11. The rail 12 thus enables the force F3 to be measured across the entire width of the fork carriage 5. This allows for flexible positioning, i.e., lateral displacement, of the fork back 4 on the fork carriage 5.

[0034] It is understood that corresponding rails can be provided at sensors 9 and 10.

[0035] In the exemplary embodiment of the Fig. 1 and Fig. 2. The industrial truck can be a counterbalance forklift or a reach truck.

Claims

[1] Method for determining the load center (L1) of a forklift truck with at least one horizontally cantilevered load handling device (1) for receiving a load (3) and at least one load handling device support (5) on which the load handling device (1) is supported in the horizontal and vertical direction, wherein at least one force (F4) acting directly from the load handling device (1) on the load handling device support (5) in the vertical direction and at least one force (F2, F3) acting directly from the load handling device (1) on the load handling device support (5) in the horizontal direction are measured directly and, given a specific geometry of the load handling device (1) and the load handling device support (5), the position of the load center (L1) of the load (3) is determined therefrom. characterized by, that a fork carriage (5) guided on a lifting mast is provided as the load-handling device carrier (5) and a fork tine (1) arranged on the fork carriage with a horizontally cantilevered fork blade (2) for receiving the load (3) and a vertically oriented fork back (4) is provided as the load-handling device (1), wherein the fork tine (1) is supported on the fork carriage (5) via the fork back (4) in the horizontal and vertical directions, and the force (F4) acting vertically downwards from the fork back (4) onto the fork carriage (5) at a support point (6) at the upper end of the fork carriage (5) and the force (F2, F3) acting horizontally from the fork back (4) onto the fork carriage (5) at a support point (6) at the upper end of the fork carriage (5) are measured directly and at a given distance between the support points (7,8) from this the horizontal distance of the load center (L1) of the load (3) from the fork back (4) or from the fork carriage (5) is determined. [2] Method according to claim 1, characterized by , that the forces (F4, F3, F2) are measured by means of sensors (9, 10, 11) arranged between the load handling device (1) and the load handling device carrier (5). [3] Method according to claim 1 or 2, characterized by that the forces (F4, F3, F2) are measured using strain gauges. [4] Method according to any one of claims 1 to 3, characterized by, that the measured values ​​from the force measurements are evaluated in a data processing unit together with values ​​stored in the data processing unit relating to the geometry of the load handling device (1) and the load handling device carrier (5), and that the load weight (F1) and the position of the load center of gravity (L1) are determined as results, and that if predefined critical results are exceeded, a warning message is issued and / or the vehicle control is intervened. [5] Industrial truck with at least one horizontally cantilevered load-handling device (1) for receiving a load (3) and at least one load-handling device support (5) on which the load-handling device (1) is supported in the horizontal and vertical direction, wherein at least one sensor (9) is provided for directly measuring a force (F4) acting directly from the load-handling device (1) on the load-handling device support (5) in the vertical direction and at least one sensor (10, 11) is provided for directly measuring a force (F2, F3) acting directly from the load-handling device (1) on the load-handling device support (5) in the horizontal direction and the sensors (9, 10, 11) are operatively connected to a data processing device which is configured to determine the position of the load center of gravity (L1) of the load (3) from the sensor data and data on the given geometry of the load-handling device (1) and the load-handling device support (5) stored in the data processing device, characterized by, that the load handling device carrier (5) is designed as a fork carriage (5) guided on a lifting mast and the load handling device (1) is designed as a fork tine (1) arranged on the fork carriage (5) with a horizontally cantilevered fork blade (2) for receiving the load (3) and a vertically oriented fork back (4), wherein the fork tine (1) is supported on the fork carriage (5) via the fork back (4) in the horizontal direction and in the vertical direction,and one of the sensors (9) is located at a support point (6) at the upper end of the fork carriage (5) for directly measuring the force (F4) acting vertically downwards from the fork back (4) onto the fork carriage (5), and one of the sensors (10) is located at a support point (7) in the upper region and / or one of the sensors (11) is located at a support point (8) in the lower region of the fork carriage (5) for directly measuring the force (F2, F3) acting horizontally from the fork back (4) onto the fork carriage (5), and the sensors (9, 10, 11) are operatively connected to the data processing unit, which is configured to determine the horizontal distance of the load center (L1) of the load (3) from the fork back (4) or fork carriage (5) from the sensor data and the distances of the support points (7, 8) stored in the data processing unit. [6] Industrial truck according to claim 5, characterized by, that the sensors (9, 10, 11) are arranged between the load handling device (1) and the load handling device support (5). [7] Industrial truck according to claim 5 or 6, characterized by , that the sensors (9, 10, 11) are designed as strain gauges. [8] Industrial truck according to any one of claims 5 to 7, characterized by that the data processing device is operatively connected to a display device and / or a vehicle control device and is configured to determine the load weight (F1) and the position of the load center of gravity (L1) from the sensor data and the stored data as results and to issue a warning message to the display device and / or intervene in the vehicle control if predefined critical results are exceeded.

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