Forklift truck with a force measuring device

Abstract

Forklift truck with a force measuring device, wherein the force measuring device is designed as a bending force measuring device (2) and additionally - at least partially - as a chassis component, characterized in that the bending force measuring device (2) has at least one elastically bendable element, wherein the bendable element is designed as a bending beam, wherein the bending beam forms a measuring section (2a, 2b, 2c, 2d) on which .Deformations caused by bending loads are measurable, wherein the bending force measuring device (2) is designed as a support body with integrally formed pendulum pins (P1, P2) for suspension on a vehicle, wherein a continuous horizontal transverse recess (Q1; Q2) is incorporated adjacent to each pendulum pin (P1; P2), which is bounded above and below by a measuring section (2a; 2b; 2c; 2d), wherein the bending force measuring device (2) has at least one measuring sensor (M1; M2; M3; M4) with which a bending of the at least one elastically bendable element can be measured, and the at least one measuring sensor (M1; M2; M3; M4) is arranged in the transverse recess (Q1, Q2) of the bending force measuring device (2).

Description

[0001] The invention relates to a forklift truck with a force measuring device, wherein the force measuring device is designed as a bending force measuring device and additionally - at least partially - as a chassis component.

[0002] JP H07-83 766 A discloses a measuring device with which the shear forces in a coupling shaft are recorded as a measure of the load on a crane's traction cable.

[0003] Forklifts can tip forward if operated improperly, especially when carrying a raised load. It is known to measure the load on the rear axle, i.e., the axle load, to determine the risk of tipping. At the start of the tipping process, the axle load is zero.

[0004] From DE 34 22 837 A1, a front-loading forklift truck with a device for measuring the load on an axle is known. In one embodiment, pressure force sensors are provided at the axle bearings to measure the axle load. This design has the disadvantage that lateral forces occurring at the axle bearings, particularly during operation, significantly distort the measurement result. In another variant, elastic deformations of the axle body are measured using a strain gauge. This design exhibits the same problems and, moreover, delivers particularly inaccurate measurement results due to the gray cast iron material typically used for axle manufacturing.

[0005] German patent DE 10 2006 028 551 A1 discloses a counterbalanced forklift truck with a front-mounted lifting device and a rear-mounted counterweight. To enable the most accurate possible measurement of the axle load, the force sensor is designed as a double shear force sensor integrated into the rear axle. This forklift truck allows for relatively simple axle load measurement without requiring any modifications to the vehicle frame, such as to the counterweight or axle suspension. However, the shear force sensor also has the disadvantage of being sensitive to force application shifts, which can lead to significant deviations between the measured value and the actual axle load, particularly during operation.

[0006] It is therefore the object of the present invention to provide a forklift truck which enables precise detection of an axle load in a reliable, robust and insensitive manner.

[0007] The problem is solved by a forklift truck characterized in that the bending force measuring device has at least one elastically bendable element, wherein the bendable element is designed as a bending beam, the bending beam forming a measuring section on which deformations caused by bending loads can be measured, the bending force measuring device being designed as a support body with molded-on pendulum pins for suspension on a vehicle, wherein a continuous horizontal transverse recess is incorporated adjacent to each pendulum pin, which is bounded above and below by a measuring section, the bending force measuring device having at least one measuring sensor with which a bending of the at least one elastically bendable element can be measured, and the at least one measuring sensor is arranged in the transverse recess of the bending force measuring device.

[0008] According to the invention, it was first recognized that retrofitting force measuring devices to or into individual axle components is both costly and leads to complex overall systems that are prone to malfunctions and, in particular, do not allow for a reliable determination of axle load. Furthermore, it was recognized that these problems cannot be effectively addressed by using highly complex special sensors, such as dual shear force sensors.

[0009] A special feature of the forklift truck according to the invention is the design of a chassis component, for example an axle component or an axle suspension component, in such a way that it simultaneously performs both a load-bearing and a measuring function. In particular, it can be advantageously provided that the chassis component is designed such that bending loads occur in a measuring section and the deformations caused by the bending load are measured by one or more measuring sensors arranged in or on the force measuring device, and the bending forces and ultimately the axle load can be determined from these measurements. With this arrangement, relatively accurate and reproducible measurements can be achieved for axle load determination.

[0010] It can be provided that the bending force measuring device is part of a central axle body of the axle attached to the vehicle frame. A simple retrofit option is then provided by replacing the central axle body of a conventional forklift truck with a central axle body equipped with the axle load detection system according to the invention.

[0011] The bending force measuring device comprises at least one elastically bendable element, which, according to the invention, is designed as a bending beam. The elastically bendable element is designed as a support body with two integrally formed, coaxial pendulum pins spaced apart from each other in the longitudinal direction of the vehicle. These pins are intended for suspending an axle from the vehicle frame, so that the support body forms a component of the axle suspension that is located within the force transmission path. Adjacent to each pendulum pin, a continuous horizontal transverse recess is incorporated into the chassis component designed as the bending force measuring device. This recess is bounded above and below by a measuring section designed as a bending beam.

[0012] It is particularly advantageous to provide that the elastically bendable element has a parallelogram linkage. This can be achieved, for example, by designing the elastically bendable element as a double bending beam. This embodiment is particularly resistant to measurement-correcting disturbances such as lateral forces and force application shifts, thus enabling reliable and precise measurement of the axle load even during driving, including on uneven road surfaces and during steering maneuvers.

[0013] The bending force measuring device has at least one measuring sensor with which a bending of the at least one elastically bendable element can be measured. In particular, in order to obtain a reproducible measurement result, it can be provided that a total of two double bending beams are equipped with a total of eight measuring sensors – 4 measuring sensors per double bending beam.

[0014] Particularly accurate results can be achieved according to the invention if additional measuring sensors are provided in a redundant manner. One embodiment is particularly reliable and accurate in which, for example, two double bending beams are equipped with a total of 16 measuring sensors – 8 measuring sensors per double bending beam.

[0015] In a further advantageous embodiment, the measurement signals of the multiple sensors are configured to calculate and / or superimpose the bending force. For example, the multiple sensors can be arranged and / or interconnected in such a way that signal components from the individual sensors relating to transverse forces, which have no overall influence on the bending, cancel each other out and / or can be calculated separately – for example, using an electronic processing and evaluation unit. Additionally or alternatively, the multiple sensors can be arranged and / or interconnected in such a way that temperature-related dependencies between the individual measurement signals of the multiple sensors largely cancel each other out – at least within a certain temperature range.

[0016] As already mentioned, to achieve particularly accurate and reliable measurements, the multiple measuring sensors can be arranged and / or interconnected in such a way that they generate redundant measurement signals. In an advantageous embodiment, at least one measuring sensor (for example, one or more strain gauges) is arranged in a plane of symmetry of the elastically deformable element, and at least one further measuring sensor is redundantly arranged on both sides of the plane of symmetry in parallel planes. The additional redundant measuring sensor can, for example, be a split strain gauge (or several split strain gauges) whose parts are electrically connected in parallel. In this way, interfering forces can be effectively compensated – even during redundant measurements.

[0017] In a particular embodiment, an electronic processing unit is provided that receives the measurement signal from one or more sensors and calculates a bending force and / or axle load from the individual signals. Additionally, a temperature sensor can be included that transmits a temperature reading to the processing unit, enabling the unit to correct temperature-related errors in the individual signals and / or the calculated bending force. In a further embodiment, a storage unit is provided to store correction parameters for different temperatures.

[0018] In a particular embodiment, the at least one measuring sensor is arranged within the bending force measuring device. The at least one measuring sensor is arranged in the transverse recess of the bending force measuring device. In a special embodiment, the bendable element has several recesses, each containing at least one measuring sensor, in particular two, and most particularly four measuring sensors.

[0019] To achieve a particularly reliable measurement result, a special embodiment provides that the measurement signals of a measuring sensor arranged in a recess can be combined with measurement signals of another measuring sensor arranged in another recess and / or that a processing unit combines the measurement signals of a measuring sensor arranged in a recess with measurement signals of another measuring sensor arranged in a recess.

[0020] The measuring sensors can, for example, be designed as strain gauges that are part of an electrical bridge circuit, in particular a Wheatstone bridge. To prevent transverse and / or torsional forces from distorting the measurement result, it can advantageously be provided that some of the strain gauges of the bridge circuit are assigned to a first measuring section and that others are assigned to a different measuring section. For example, some of the strain gauges of the bridge circuit can be arranged in a first recess of the bending force measuring device, while others are arranged in a different recess of the bending force measuring device.

[0021] A particularly reliable version of the bending force measuring device is one that incorporates multiple measuring circuits, for example, redundant ones. Specifically, according to the invention, some strain gauges can be configured as part of a first electrical bridge circuit, while others are configured as part of a second electrical bridge circuit. Furthermore, a particularly reliable and reproducible measurement result can be achieved if some strain gauges of the first electrical bridge circuit are assigned to a first measuring range, for example, a first recess, while others are assigned to a second measuring range, for example, a second recess.Furthermore, it can also be advantageously provided that some of the strain gauges of the second electrical bridge circuit are assigned to the first measuring range, for example the first recess, while others of the strain gauges of the second electrical bridge circuit are assigned to the second measuring range, for example the second recess.

[0022] In a special design, a protective device is provided to protect the measuring sensor(s) from contamination and / or damage. This protective device may, for example, include a shrink ring or be designed as a shrink ring. It may also be provided that at least one measuring sensor is located under a protective potting compound.

[0023] In a particularly advantageous embodiment of the forklift truck according to the invention, the bending force measuring device is designed as an axle, in particular as a rear axle and / or as a steering axle, and / or as a component of an axle suspension. The bending force measuring device is designed as a support body with integrally formed – in particular coaxial – pendulum pins for suspension on a vehicle, in particular on a vehicle frame.

[0024] Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiments shown in the schematic figures. These show: Fig. 1 a perspective view of a central axis body of an axle of a forklift truck according to the invention, Fig. 2 a side view of a bending force measuring device designed as a support body of the central axis body, and Fig. 3 schematically a possible assignment of the measuring sensors to the measuring circuits.

[0025] Fig. Figure 1 shows the central axle body 1 of a rear-mounted (steering) axle designed as a steering axle of a four-wheel forklift truck according to the invention. It is also conceivable, in principle, to use the invention in three-wheel forklift trucks. A bending force measuring device 2, designed as a support body, is attached to the central axle body 1, for example by bolting, and forms part of the central axle body 1 and thus of the axle. The bending force measuring device 2 not only serves to measure the axle load, as will be described later, but also represents an axle component arranged in the force flow, by means of which the axle is pivotally suspended from a vehicle frame (e.g., a counterweight as part of the vehicle frame) of the forklift truck, which is not shown in the figures.

[0026] For the aforementioned purpose, the bending force measuring device 2, designed as a support body (see also Fig. 2) via two integrally formed, coaxial pendulum pins P1, P2, which are spaced apart from each other in the longitudinal direction of the vehicle and are designed to engage in elastic axle bearings connected to the vehicle frame.

[0027] Adjacent to each pendulum pin P1 or P2, a continuous horizontal transverse recess Q1 or Q2 is incorporated into the bending force measuring device 2.

[0028] Each transverse recess Q1 or Q2 is limited upwards and downwards by measuring sections 2a, 2b or 2c, 2d of the bending force measuring device 2, which are designed as bending beams.

[0029] The axle forces F A The forces are introduced axially between the two transverse recesses Q1, Q2 into the bending force measuring device 2. The support forces F act on the pendulum pins P1, P1. R of the vehicle frame. The measuring sections 2a, 2b, 2c and 2d, designed as bending beams, are therefore subjected to bending stress and are (slightly) deformed under appropriate load.

[0030] These deformations, which occur as compressions and strains of the outer fibers of the surfaces of the measuring sections 2a, 2b, 2c and 2d, are preferably measured by sensors, in particular strain gauges, arranged within the transverse recesses Q1 and Q2 on the inner surfaces of the measuring sections 2a, 2b, 2c and 2d. Attaching the strain gauges to the (rounded) transitions between the measuring sections 2a, 2b, 2c, 2d and the vertical walls of the transverse recesses Q1, Q2 has proven to be particularly suitable.

[0031] Alternatively or additionally, strain gauges can also be attached to the outer surfaces of measuring sections 2a, 2b, 2c, and 2d outside the transverse recesses Q1 and Q2. Furthermore, for certain applications, it may suffice to measure deformations on only some of the measuring sections 2a, 2b, 2c, and 2d, rather than all of them, and to determine bending forces and thus the axle load. However, measuring a larger number of sections allows for a very precise determination of the axle load, as interfering forces and moments can be factored out.

[0032] Of course, it is also possible to measure bending forces at other suitable points on the axle and, for this purpose, to design structural components of the axle wholly or partially as bending force measuring devices. For example, bending forces acting on steerable steering knuckles, which are pivotably mounted to the axial ends of the central axle body 1, can be recorded. In this case, a measuring section arranged axially between a kingpin and a wheel hub bearing on the steering knuckle is designed as a bending beam.

[0033] Fig. Figure 3 shows an embodiment comprising a first measuring circuit 3 and a second measuring circuit 4. The figure also schematically illustrates the assignment of measuring sensors M1, M2, M3, and M4 to the measuring circuits 3 and 4, enabling a particularly reliable measurement of an axle load, largely unaffected by transverse and torsional forces. Measuring sensors M1 and M2, designed as strain gauges, are arranged in the transverse recess Q1, while the other measuring sensors M3 and M4, also designed as strain gauges, are arranged in the other transverse recess Q2. The first measuring circuit 3 receives the measurement signals from measuring sensors M1 and M4, which are arranged in different transverse recesses Q1 and Q2, while the second measuring circuit 4 receives the measurement signals from measuring sensors M2 and M3, which are arranged in different transverse recesses Q1 and Q2. Fig.Figure 3 schematically illustrates the measuring arrangement. Advantageously, further measuring sensors can be provided in the transverse recesses Q1, Q2, which are connected to the measuring circuits 3, 4 in the same way.

[0034] The invention has been described with regard to a particular embodiment. However, it is understood that modifications and adaptations can be made without departing from the scope of protection of the following claims. Reference symbol list: 1 Central axle body 2 Bending force measuring device 2a, 2b, 2c 2d Measurement sections 3 First measuring circuit 4 Second measuring circuit F A Axle forces F R Support forces P1, P2 pendulum pivot Q1, Q2 transverse recesses M1, M2, M3, M4 measuring sensors

Claims

[1] Forklift truck with a force measuring device, wherein the force measuring device is designed as a bending force measuring device (2) and additionally - at least partially - as a chassis component, characterized by, that the bending force measuring device (2) has at least one elastically bendable element, wherein the bendable element is designed as a bending beam, wherein the bending beam forms a measuring section (2a, 2b, 2c, 2d) at which . Deformations caused by bending loads are measurable, wherein the bending force measuring device (2) is designed as a support body with integrally formed pendulum pins (P1, P2) for suspension on a vehicle, wherein a continuous horizontal transverse recess (Q1; Q2) is incorporated adjacent to each pendulum pin (P1; P2), which is bounded above and below by a measuring section (2a; 2b; 2c; 2d), wherein the bending force measuring device (2) has at least one measuring sensor (M1; M2; M3; M4) with which a bending of the at least one elastically bendable element can be measured, and the at least one measuring sensor (M1; M2; M3; M4) is arranged in the transverse recess (Q1, Q2) of the bending force measuring device (2). [2] Forklift truck according to claim 1, characterized by that the elastically bendable element has a parallelogram guide. [3] Forklift truck according to claim 1 or 2, characterized by that the elastically bendable element is designed as a double bending beam. [4] Forklift truck according to any one of claims 1 to 3, characterized by , that the bending force measuring device (2) has several measuring sensors (M1; M2; M3; M4). [5] Forklift truck according to claim 4, characterized by , that the measurement signals of the several measuring sensors (M1; M2; M3; M4) are calculated and / or superimposed to determine the bending force. [6] Forklift truck according to one of claims 4 or 5, characterized bythat the multiple measuring sensors (M1, M2, M3, M4) are arranged and / or interconnected in such a way that signal components of the individual measuring sensors (M1, M2, M3, M4), which relate to transverse forces also recorded, which have no overall influence on the bending, cancel each other out and / or can be calculated against each other. [7] Forklift truck according to any one of claims 4 to 6, characterized by , that the multiple measuring sensors (M1, M2, M3, M4) are arranged and / or interconnected in such a way that temperature-related dependencies of the individual measuring signals of the multiple measuring sensors (M1, M2, M3, M4) largely cancel each other out - at least in one temperature range. [8] Forklift truck according to any one of claims 4 to 7, characterized by that the multiple measuring sensors (M1, M2, M3, M4) are arranged and / or interconnected in such a way that they generate mutually redundant measurement signals. [9] Forklift truck according to any one of claims 4 to 8, characterized by , that at least one measuring sensor (M1; M2; M3; M4) is provided in a plane of symmetry of the elastically deformable element and that a redundant measuring sensor (M1; M2; M3; M4) is arranged on both sides of the plane of symmetry in parallel planes. [10] Forklift truck according to any one of claims 1 to 9, characterized by , that an electronic processing unit is provided which receives the measurement signal of the one measuring sensor (M1; M2; M3; M4) or the measurement signals of the several measuring sensors (M1, M2, M3, M4). [11] Forklift truck according to claim 10, characterized by that the processing unit determines a bending force from the individual measurement signals. [12] Forklift truck according to one of claims 10 or 11, characterized by , that a temperature measuring device is provided and that the processing unit corrects temperature-related measurement errors of the individual measurement signals and / or the determined bending force. [13] Forklift truck according to any one of claims 10 to 12, characterized by that a storage unit is provided in which correction parameters for different temperatures are stored. [14] Forklift truck according to any one of claims 1 to 13, characterized by , that at least one measuring sensor (M1; M2; M3; M4) has a strain gauge. [15] Forklift truck according to any one of claims 1 to 14, characterized by , that the bending force measuring device (2) has several recesses in which at least one measuring sensor (M1; M2; M3; M4) is arranged. [16] Forklift truck according to any one of claims 1 to 15, characterized by, that the measurement signals of a measuring sensor (M1; M2; M3; M4) assigned to a measuring section (2a; 2b; 2c; 2d) are computable with measurement signals of another measuring sensor (M1; M2; M3; M4) assigned to another measuring section (2a; 2b; 2c; 2d) and / or that a processing unit computes the measurement signals of a measuring sensor (M1; M2; M3; M4) assigned to a measuring section (2a; 2b; 2c; 2d) with measurement signals of another measuring sensor (M1; M2; M3; M4) assigned to another measuring section (2a; 2b; 2c; 2d). [17] Forklift truck according to any one of claims 1 to 16, characterized by , that the measuring sensors (M1; M2; M3; M4) are designed as strain gauges which are part of an electrical bridge circuit. [18] Forklift truck according to claim 17, characterized by, that some of the strain gauges of the bridge circuit are arranged in one recess of the bending force measuring device (2) and that other strain gauges of the bridge circuit are arranged in another recess of the bending force measuring device (2). [19] Forklift truck according to any one of claims 1 to 18, characterized by , that the measuring sensors (M1; M2; M3; M4) are designed as strain gauges and that some of the strain gauges are part of a first electrical bridge circuit and that others of the strain gauges are part of a second electrical bridge circuit. [20] Forklift truck according to any one of claims 1 to 19, characterized by , that a protective device is provided which protects the measuring sensor(s) (M1; M2; M3; M4) from contamination and / or damage. [21] Forklift truck according to claim 20, characterized by that the protective device has a shrink ring. [22] Forklift truck according to any one of claims 1 to 21, characterized by , that at least one measuring sensor (M1; M2; M3; M4) is arranged under a protective potting compound. [23] Forklift truck according to any one of claims 1 to 22, characterized by , that the bending force measuring device (2) is designed as an axle and / or as a component of an axle suspension. [24] Forklift truck according to any one of claims 1 to 23, characterized by , that the bending force measuring device (2) is designed as a support body with molded pendulum pins (P1, P2) for suspension on a vehicle frame of the vehicle. [25] Forklift truck according to any one of claims 1 to 24, characterized by , that the bending force measuring device (2) is designed to determine an axle load.

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