Truck-mounted crane force limit calculation method

Abstract

The invention discloses a truck-mounted crane force limit calculation method which comprises the following steps: S1, acquiring rodless cavity oil pressure, rod cavity oil pressure, main arm length and amplitude variation angle of an amplitude variation oil cylinder in real time, and calculating the thrust of the amplitude variation oil cylinder based on structural parameters of the amplitude variation oil cylinder; s2, establishing a geometric model of a main arm-variable-amplitude oil cylinder, and calculating the length of a force arm of the variable-amplitude oil cylinder relative to a lower hinge point of the main arm; s3, fitting the gravity center position of the main arm through a polynomial, and calculating a gravity center force arm of the main arm; s4, force arms of the lifting hook and the load relative to the lower twisting point of the main arm are calculated; s5, the load weight is solved according to the fact that the product of the thrust of the variable-amplitude oil cylinder and the force arm is equal to the total torque of the main arm self-weight, the lifting hook self-weight and the load; the precision, efficiency and adaptability of force limit calculation are remarkably improved through the dynamic calculation model, polynomial fitting calibration and geometric modeling optimization.

Description

Technical Field

[0001] This invention belongs to the field of engineering machinery technology, and in particular, relates to a method for calculating the force limit of a truck-mounted crane. Background Technology

[0002] A truck-mounted crane, also known as a truck-mounted crane, is a special type of engineering vehicle that integrates lifting equipment (cranes) directly onto a transport vehicle (usually a truck chassis). The load limit system (often called a torque limiter or load torque indicator) is the most critical and core safety protection system of the truck-mounted crane. Its function is to monitor and prevent overloading and tipping accidents during operation. It directly relates to the safety of equipment, personnel, and goods.

[0003] Most existing methods for calculating the force limit are based on the principle of torque balance: the thrust of the luffing cylinder is calculated using a hydraulic pressure sensor, and the lifting weight is calculated using the torque balance principle. That is, during lifting operations, when the boom system is in a stable state, the clockwise torque generated by all forces is equal to the counterclockwise torque (the total torque is zero). When operating a truck-mounted crane, two main types of torques are involved: the overturning moment generated by the load and the balancing moment. The formulas are as follows: Where F1 represents the force on the rodless chamber of the luffing cylinder, and F2 represents the force on the rod chamber of the luffing cylinder, F f For the friction force of the luffing cylinder, L b This indicates the lever arm of the luffing cylinder, the weight of the object being lifted, n, and L. r R represents the lever arm of the hoisting wire rope tension, R represents the working radius, self-weight represents the weight of the boom itself, and R′ represents the lever arm of the boom's own weight.

[0004] Due to the frictional force F of the hydraulic cylinder f Precise calibration is difficult and fluctuates with equipment wear and temperature changes, typically requiring extensive real-vehicle testing. Friction is affected by various factors such as cylinder seals, movement speed, cylinder machining deviations, and the external environment, making precise calibration challenging. This leads to significant discrepancies between the calculated weight (G) and the actual lifting weight (more pronounced under no-load or light-load conditions), and calibration compensation is difficult to perform, posing a risk of overloading and potentially damaging or overturning the boom, resulting in serious safety hazards. Furthermore, the boom's center of gravity dynamically changes during extension and retraction, and manufacturing errors (such as uneven material density) can distort the calculation of self-weight torque. The torque balance principle is primarily applicable to static or uniform-speed lifting scenarios, but actual operations (such as during lifting or boom luffing) generate impact loads or inertial forces. These dynamic forces are not included in the static equilibrium equations, potentially leading to conservative or risky force limit calculations.

[0005] Existing patent application CN117416866A discloses a crane force limiter system and weight calculation method, including a force limiter main unit, a display, a length sensor, an angle sensor, and a cylinder thrust sensor. The cylinder thrust sensor is installed on the luffing cylinder. The length sensor, angle sensor, and cylinder thrust sensor are each communicatively connected to the force limiter main unit to transmit their respective collected data. The force limiter main unit is communicatively connected to the display, receiving and processing the data from each sensor before transmitting the processed information to the display. The display receives the information from the force limiter main unit and displays it to the operator in real time. This patent uses the hydraulic pressure of the luffing cylinder for conversion. Due to the influence of cylinder friction, the luffing hydraulic pressure fluctuates. Furthermore, the cylinder length fluctuates due to cylinder settling, and the weight of the hydraulic fluid inside the cylinder varies, causing deviations in the force limiter's weight calculation. The measurement accuracy, especially under small loads, is low, and the calculation process is not addressed. Summary of the Invention

[0006] This invention mainly addresses the issue of hydraulic cylinder friction force F in existing technologies. f It is difficult to calibrate accurately and fluctuates with equipment wear and temperature changes. It usually requires a large number of actual vehicle test conditions for calibration. Since the friction force is affected by many factors such as cylinder seal, movement speed, cylinder machining deviation and external environment, the friction force is difficult to calibrate accurately, resulting in a large deviation between the calculated weight of G and the actual lifting weight. Therefore, a method for calculating the force limit of truck crane is proposed.

[0007] A method for calculating the force limit of a truck-mounted crane includes the following steps: S1. Real-time acquisition of the rodless chamber oil pressure, rod chamber oil pressure, and boom length of the luffing cylinder. and amplitude angle Calculate the thrust of the luffing cylinder based on its structural parameters. ; S2. Establish the geometric model of the main boom-luffing cylinder. Using the geometric coordinate relationship between the upper and lower control points of the luffing cylinder, and combining this with the point-to-line distance formula, calculate the lever arm length of the luffing cylinder relative to the lower control point of the main boom. ; S3. Based on calibration data, and by polynomial fitting, the main arm's center of gravity and main arm length are correlated. Based on the relationship and the torque balance, the distance from the boom's center of gravity to the boom's lowering point can be calculated. And calculate the lever arm of the main arm's center of gravity. ; S4. Based on the main arm length and amplitude angle Calculate the lever arm of the hook and load relative to the lower pivot point of the main boom; S5. Based on the fact that the product of the luffing cylinder thrust and the lever arm equals the total torque of the main boom's self-weight, the hook's self-weight, and the load, the load weight can be calculated. Its expression is

[0008] In the formula, This represents the total weight of the main boom system. Indicates the weight of the hook. This indicates the lever arm of the lifting hook.

[0009] Further, in step S1, the thrust calculation formula for the luffing cylinder is as follows:

[0010] In the formula, Indicates the oil pressure in the rodless chamber. Indicates the oil pressure in the rod chamber. Indicates the effective area of ​​the rodless cavity. This indicates the effective area of ​​the rod cavity.

[0011] Furthermore, in step S2, the variable amplitude cylinder arm The calculations include: S21. Establish a coordinate system oxy with the lower boom yoke point as the origin o, and determine the coordinates of the upper boom yoke point E of the luffing cylinder as follows: ,in, The distance from point O to point E; S22. Establish a coordinate system o1x1y1 with the lower pivot point o1 of the luffing cylinder as the origin. The intersection of the two coordinate systems is point D. Calculate the coordinates of point E in o1x1y1.

[0012] In the formula, This represents the distance from o1 to the intersection point D of the coordinate system. This represents the distance from point O to point D; S23. Solve for the slope of the center line of the variable amplitude cylinder. ;Right now ; S24. The lever arm of the variable amplitude cylinder is calculated using the point-to-line straight-line distance formula, and its expression is:

[0013] Wherein, the coordinates of point o in the o1x1y1 coordinate system are ( ).

[0014] Furthermore, the x-axis of the coordinate system oxy is along the horizontal direction, the y-axis is along the vertical direction, and the amplitude angle is... The angle between the x-axis and the main arm axis is denoted as .

[0015] Further, in step S3, the polynomial fitting includes: fixing the amplitude angle under no-load conditions. Change the length of the main arm Then record the thrust of the variable amplitude cylinder. According to the thrust of the variable amplitude cylinder Derivation of the theoretical center of gravity of the main arm The mapping relationship between the centroid of the main arm and the length of the main arm is established by fitting a curve using a sixth-order polynomial. The expression is as follows:

[0016] In the formula, Indicates the total length of the main arm. This indicates the distance from the boom's center of gravity to the boom's lower yoke point. This represents the coefficient obtained by fitting the theoretical main boom center of gravity and main boom length through the thrust of multiple sets of hydraulic cylinders.

[0017] Furthermore, in step S3, the thrust of the luffing cylinder... The torque generated at the lower control point of the main boom is always in equilibrium with the torque generated by the weight of the main boom at the lower control point, that is:

[0018] In the formula, This indicates the length of the main boom's center of gravity from the main boom's lower auger point. The lever arm that represents the center of gravity of the main arm.

[0019] Furthermore, the lever arm of the main arm's center of gravity is .

[0020] Furthermore, the total gravity of the main arm system The equivalent gravity includes the main boom, telescopic cylinder, and wire rope, and its point of application is dynamically determined through calibration fitting.

[0021] Furthermore, in step S4, the load and the lever arm of the hook relative to the lowering point of the main boom are both... .

[0022] Furthermore, the weight of the hook This can be a preset constant or obtained in real time via a pressure sensor.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention eliminates theoretical center-of-gravity deviations caused by production and assembly errors by back-calculating the position of the main boom's center of gravity using a sixth-order polynomial fitting of the main boom's center of gravity and length under no-load conditions, reducing the measured error to ≤5%. By establishing a dual coordinate system (the oxy coordinate system of the main boom's lower pivot point and the o1x1y1 coordinate system of the hydraulic cylinder's lower pivot point), and combining angle sensor data, the lever arm length is calculated in real time. This solves the problem of accumulated error in simplified models, and significantly improves accuracy, especially under large-angle variable amplitude conditions.

[0024] 2. In the calculation process, this invention directly uses the thrust of the luffing cylinder, ignoring the friction of the luffing cylinder, to calculate the thrust and then derive the theoretical center of gravity position of the main boom. The relationship between the center of gravity position of the main boom and the length of the main boom is fitted. Using a holistic approach, the actual measurable luffing cylinder pressure and its relationship with the length of the main boom are automatically fitted into a curve relationship using a large amount of data. This avoids errors caused by substituting difficult-to-predict parameters such as the friction of the luffing cylinder, assembly errors of the main boom, uneven material density distribution, and deformation into the torque calculation. Attached Figure Description

[0025] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the main arm model of the present invention; Figure 3 This is a schematic diagram of the coordinate system model of the present invention (I); Figure 4 This is a schematic diagram (II) of the coordinate system model of the present invention.

[0026] In the above diagram, 1. Main boom lower winding point; 2. Luffing cylinder upper winding point; 3. Luffing cylinder lower winding point. Detailed Implementation

[0027] To clearly illustrate the technical features of the present invention, the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below. In the present invention, unless otherwise expressly specified and limited, the first feature "on" or "below" the second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] Example 1 like Figure 1 As shown, a method for calculating the force limit of a truck-mounted crane includes the following steps: S1. Real-time acquisition of the rodless chamber oil pressure, rod chamber oil pressure, and boom length of the luffing cylinder. and amplitude angle Calculate the thrust of the luffing cylinder based on its structural parameters. ; S2. Establish the geometric model of the main boom-luffing cylinder. Using the geometric coordinate relationship between the upper control point 2 and the lower control point 3 of the luffing cylinder, and combining this with the point-to-line distance formula, calculate the lever arm length of the luffing cylinder relative to the lower control point 1 of the main boom. ; S3. Based on calibration data, and by polynomial fitting, the main arm's center of gravity and main arm length are correlated. Based on the relationship and the torque balance, the distance from the main boom's center of gravity to the main boom's lower yoke point 1 can be calculated. And calculate the lever arm of the main arm's center of gravity. ; S4. Based on the main arm length and amplitude angle Calculate the lever arm of the hook and load relative to the lower pivot point 1 of the main boom; S5. Based on the fact that the product of the luffing cylinder thrust and the lever arm equals the total torque of the main boom's self-weight, the hook's self-weight, and the load, the load weight can be calculated. Its expression is

[0029] In the formula, This represents the total weight of the main boom system. Indicates the weight of the hook. This indicates the lever arm of the lifting hook.

[0030] This embodiment details the force limit calculation process for truck-mounted cranes operating in scenarios with medium boom lengths (e.g., 8m, length sampling value 1690) and conventional luffing angles (e.g., 60°). Specific parameters and steps are as follows: Parameter preparation: Calculate the structural parameters of the luffing cylinder, including the effective area of ​​the rodless chamber. Effective area of ​​the rod cavity The total weight of the main boom system is known. The hook has a preset weight. The sensor detects parameters in real time, including the oil pressure in the rodless chamber. Rod chamber hydraulic pressure Total length of main arm Variable angle .

[0031] In this embodiment, the thrust of the luffing cylinder is calculated: the thrust of the luffing cylinder is mainly calculated using the cylinder's structural dimensions and the oil pressure in the rod-side and rodless-side chambers detected by the oil pressure sensor. The thrust is calculated using the cylinder thrust calculation formula, the expression of which is:

[0032] Calculate the lever arm of the variable amplitude cylinder: such as Figure 2 and Figure 3 As shown, the lowering point of the main boom is denoted as point O. All points on the main boom then undergo circular motion around point O. A coordinate system oxy is established with point O, where the x-axis is horizontal and the y-axis is vertical, and the amplitude angle is [not specified]. The angle between the x-axis and the main arm axis; The upper winch point of the luffing cylinder is denoted as point E, and the distance between point E and point O is denoted as... This point is the connection point between the luffing cylinder and the fixed main boom. It can move in a circle around the lower pivot point of the main boom. Therefore, the expression for point E in the coordinate system is:

[0033] Establish a coordinate system o1x1y1 with the lower pivot point o1 of the variable amplitude cylinder as the origin. The intersection of the two coordinate systems is point D. Calculate the coordinates of point E in o1x1y1.

[0034] In the formula, This represents the distance from o1 to the intersection point D of the coordinate system. This represents the distance from point O to point D; like Figure 4 As shown, the lever arm of the luffing cylinder is the distance from point o to the luffing cylinder, denoted as . Then the center line of the variable amplitude cylinder can be expressed in the coordinate system o1x1y1 as:

[0035]

[0036] After substituting the values, we get ; Where the coordinates of point o in the o1x1y1 coordinate system are: The lever arm of the variable amplitude cylinder is calculated using the point-to-line distance formula, and its expression is:

[0037] Calculation of the boom's center of gravity and lever arm: In the unloaded state, the weight of the boom remains constant, but its center of gravity changes with the extension and retraction of the boom, causing a torque generated at the boom's lower pivot point due to the boom's weight. Specifically, in the unloaded state, the luffing angle is fixed. Change the length of the main arm Then record the thrust of the variable amplitude cylinder. The mapping relationship between the main boom's center of gravity and its length was established using a sixth-order polynomial fitting curve. During the calibration process, With the thrust of the variable amplitude cylinder If the relationship between them is a fixed linear proportional relationship, then we can derive... and Similarly, there exists a polynomial fitting equation, whose expression is:

[0038] In the formula, Indicates the total length of the main arm. This indicates the distance from the boom's center of gravity to the boom's lower yoke point. This represents the coefficient obtained by fitting the main arm's center of gravity and main arm length; In this embodiment, the coefficients of the sixth-order polynomial are obtained by fitting the calibration data using the least squares method:

[0039]

[0040] Substituting the length sample value of 1690 at this time, we get ; Based on the torque balance relationship, the thrust of the variable amplitude cylinder... The torque generated at the lower control point of the main boom is always in equilibrium with the torque generated by the weight of the main boom at the lower control point, that is:

[0041] In the formula, The lever arm representing the center of gravity of the main boom; substituting the magnitude of the thrust of the luffing cylinder, we can obtain the lever arm of the center of gravity of the main boom as follows: ; Hook and load lever arm calculation: The lever arms of the load and the hook relative to the lowering point of the main boom are both... ; Load weight calculation: The upward vertical force comes solely from the luffing cylinder, while the downward force comes from the weight of each boom section, the weight of the boom extension cylinder, the weight of the wire rope, the weight of the hook, and the weight of the load. All these forces act uniformly at the lower control point of the boom. According to the torque balance relationship, the upward vertical torque is equal to the downward vertical torque. This represents the total weight of the main boom system. Indicates the weight of the hook. Indicate the lever arm of the hook; solve for the load weight. Its expression is

[0042] Substitution .

[0043] In this embodiment, with a medium main boom length and a conventional angle, the load weight calculated through the above steps is approximately 1.0029 tons. Compared with a 1-ton weight, the error is 0.29%, which is far less than the industry standard of 5%.

[0044] Example 2 like Figure 1 As shown, a method for calculating the force limit of a truck-mounted crane includes the following steps: S1. Real-time acquisition of the rodless chamber oil pressure, rod chamber oil pressure, and boom length of the luffing cylinder. and amplitude angle Calculate the thrust of the luffing cylinder based on its structural parameters. ; S2. Establish the geometric model of the main boom-luffing cylinder. Using the geometric coordinate relationship between the upper control point 2 and the lower control point 3 of the luffing cylinder, and combining this with the point-to-line distance formula, calculate the lever arm length of the luffing cylinder relative to the lower control point 1 of the main boom. ; S3. Based on calibration data and by fitting the thrust of the variable amplitude cylinder using a polynomial... With the length of the main arm Based on the relationship and the torque balance, the distance from the main boom's center of gravity to the main boom's lower yoke point 1 can be calculated. And calculate the lever arm of the main arm's center of gravity. ; S4. Based on the main arm length and amplitude angle Calculate the lever arm of the hook and load relative to the lower pivot point 1 of the main boom; S5. Based on the fact that the product of the luffing cylinder thrust and the lever arm equals the total torque of the main boom's self-weight, the hook's self-weight, and the load, the load weight can be calculated. Its expression is

[0045] In the formula, This represents the total weight of the main boom system. Indicates the weight of the hook. This indicates the lever arm of the lifting hook.

[0046] This embodiment details the force limit calculation process for truck-mounted cranes operating in scenarios with medium boom lengths (e.g., 10m, sampling value 2041) and conventional luffing angles (e.g., 60°). Specific parameters and steps are as follows: Parameter preparation: Calculate the structural parameters of the luffing cylinder, including the effective area of ​​the rodless chamber. Effective area of ​​the rod cavity The total weight of the main boom system is known. The hook has a preset weight. The sensor detects parameters in real time, including the oil pressure in the rodless chamber. Rod chamber hydraulic pressure Total length of main arm Variable angle ; In this embodiment, the thrust of the luffing cylinder is calculated: the thrust of the luffing cylinder is mainly calculated using the cylinder's structural dimensions and the oil pressure in the rod-side and rodless-side chambers detected by the oil pressure sensor. The thrust is calculated using the cylinder thrust calculation formula, which is expressed as follows: Calculate the lever arm of the variable amplitude cylinder: such as Figure 2 and Figure 3 As shown, the lowering point of the main boom is denoted as point O. All points on the main boom then undergo circular motion around point O. A coordinate system oxy is established with point O, where the x-axis is horizontal and the y-axis is vertical, and the amplitude angle is [not specified]. The angle between the x-axis and the main arm axis; The upper winch point of the luffing cylinder is denoted as point E, and the distance between point E and point O is denoted as... This point is the connection point between the luffing cylinder and the fixed main boom. It can move in a circle around the lower pivot point of the main boom. Therefore, the expression for point E in the coordinate system is:

[0047] Establish a coordinate system o1x1y1 with the lower pivot point o1 of the variable amplitude cylinder as the origin. The intersection of the two coordinate systems is point D. Calculate the coordinates of point E in o1x1y1.

[0048] In the formula, This represents the distance from o1 to the intersection point D of the coordinate system. This represents the distance from point O to point D; like Figure 4 As shown, the lever arm of the luffing cylinder is the distance from point o to the luffing cylinder, denoted as . Then the center line of the variable amplitude cylinder can be expressed in the coordinate system o1x1y1 as:

[0049]

[0050] After substituting the values, we get ; Where the coordinates of point o in the o1x1y1 coordinate system are: The lever arm of the variable amplitude cylinder is calculated using the point-to-line straight-line distance formula, and its expression is:

[0051] Calculation of boom center of gravity and lever arm: Under no-load conditions, fix the luffing angle. Change the length of the main arm Then record the thrust of the variable amplitude cylinder. According to the thrust of the variable amplitude cylinder Derivation of the theoretical center of gravity of the main arm The mapping relationship between the center of gravity and length of the main arm is established by fitting a curve using a sixth-order polynomial. Its expression is:

[0052] In the formula, Indicates the total length of the main arm. The coefficients are obtained by fitting multiple sets of main arm center of gravity and main arm length. In this embodiment, the sixth-order polynomial coefficients are obtained by fitting the calibration data using the least squares method:

[0053]

[0054] Substitution (Length sampling value is 2041), the center of gravity of the main arm is obtained as follows: ; Based on the torque balance relationship, the thrust of the variable amplitude cylinder... Torque and main arm gravity The torque balance, that is:

[0055] In the formula, This indicates the length of the main boom's center of gravity from the main boom's lower auger point. The lever arm represents the center of gravity of the main boom; substituting this into the magnitude of the thrust of the luffing cylinder yields the result. ; The lever arm of the main arm's center of gravity is ; Hook and load lever arm calculation: The lever arms of the load and the hook relative to the lowering point of the main boom are both... ; Load weight calculation: The upward vertical force comes solely from the luffing cylinder, while the downward force comes from the weight of each boom section, the weight of the boom extension cylinder, the weight of the wire rope, the weight of the hook, and the weight of the load. All these forces act uniformly at the lower control point of the boom. According to the torque balance relationship, the upward vertical torque is equal to the downward vertical torque. This represents the total weight of the main boom system. Indicates the weight of the hook. Indicate the lever arm of the hook; solve for the load weight. Its expression is

[0056] The conclusion is .

[0057] In this embodiment, under medium boom length and conventional angle, the calculated load weight through the above steps is approximately 2.075179 tons, with an error of 3.75% compared to a 1-ton weight, meeting the industry standard of 5% error. Unloading and force limit alarms are implemented according to different operating conditions.

[0058] Example 3 In this embodiment, an adaptive calibration function for abnormal operating conditions is added. The calibration trigger condition is: when the load weight is detected to be <0 or the fluctuation of the calculation result is >10% for 5 consecutive times, it is determined that recalibration is required.

[0059] The automatic calibration process is as follows: Control the truck-mounted crane to return to a safe position and unload the load; At multiple amplitude angles The main boom automatically extends to its full range of motion. Real-time acquisition of the thrust of the luffing cylinder and the total length of the main boom, updating the coefficients of the sixth-order polynomial. ; Temperature sensor data is incorporated into hydraulic pressure calculations to dynamically correct the effective area of ​​the hydraulic cylinder. This resolves long-term errors caused by cylinder wear and temperature drift.

[0060] Obviously, the embodiments described above are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of calculating a force limit of a truck-mounted crane, characterized by, The method comprises the following steps: S1. Real-time acquisition of the rodless chamber oil pressure, rod chamber oil pressure, and boom length of the luffing cylinder. and amplitude angle Calculate the thrust of the luffing cylinder based on its structural parameters. ; S2, a geometric model of the main arm-amplitude cylinder is established, and an arm length of the amplitude cylinder relative to a lower winding point of the main arm is calculated by a geometric coordinate relationship between an upper winding point on the amplitude cylinder and the lower winding point of the amplitude cylinder, and a point-to-line distance formula ; S3. Based on calibration data, and by polynomial fitting, the main arm's center of gravity and main arm length are correlated. Based on the relationship and the torque balance, the distance from the boom's center of gravity to the boom's lowering point can be calculated. And calculate the lever arm of the center of gravity of the main arm. ; S4, based on the main boom length and the angle of deflection , calculate the force arm of the hook relative to the load from the main boom lower point S5, according to the amplitude of the cylinder thrust and arm product equal to the main arm weight, hook weight and load total moment, to solve the load weight The expression is wherein Gtotal represents the total weight force of the main arm system, Ghook represents the weight force of the hook, Lhook represents the hook force arm.

2. The method of claim 1, wherein, In the step S1, a pushing force calculation formula of the amplitude cylinder is In the formula, represents the rodless chamber oil pressure, represents the rod chamber oil pressure, represents the rodless chamber effective area, represents the rod chamber effective area.

3. The method of claim 1, wherein, In the step S2, the force arm of the variable amplitude cylinder calculation includes: S21, establish a coordinate system oxy with the main arm lower purchase point as the origin o, determine the coordinates of the upper purchase point E of the amplitude cylinder as wherein, is the distance from the point o to the point E; S22, a coordinate system o1x1y1 is established with the lower hoisting point o1 of the amplitude cylinder as the origin, the intersection of the two coordinate systems is point D, and the coordinates of point E in o1x1y1 are calculated wherein represents the distance from o1to the intersection point D of the coordinate system, represents the distance from o to D. S23, the center straight line slope of the variable amplitude oil cylinder is solved as ; that is ; S24, the force arm of the amplitude cylinder is calculated by a point-to-line straight line distance formula, and the expression is Wherein, the coordinate of point o in the o1x1y1 coordinate system is (x1, y1) ).

4. The method of calculating the force limit of a truck-mounted crane according to claim 3, characterized in that, The x-axis of the coordinate system oxy is along the horizontal direction, the y-axis is along the vertical direction, and the amplitude angle is the included angle between the x-axis and the main arm axis.

5. The method of calculating the load limit of a truck-mounted crane according to claim 1, characterized in that, In step S3, the polynomial fitting includes: fixing the amplitude angle under no-load conditions. Change the length of the main arm Then record the thrust of the variable amplitude cylinder. According to the thrust of the variable amplitude cylinder Derivation of the theoretical center of gravity of the main arm The mapping relationship between the centroid of the main arm and the length of the main arm is established by fitting a curve using a sixth-order polynomial. The expression is as follows: wherein L represents the total length of the main boom, D represents the distance from the center of gravity of the main boom to the lower point of the main boom, C represents the coefficient obtained by fitting the theoretical center of gravity of the main boom and the length of the main boom calculated by the thrust of the plurality of oil cylinders.

6. The method of calculating the load limit of a truck-mounted crane according to claim 1, characterized in that, The step S3, the amplitude cylinder thrust The moment generated at the main arm lower purchase point and the main arm gravity moment generated at the main arm lower purchase point is always in balance, that is: wherein represents the length of the main arm center of gravity from the main arm lower purchase point, represents the length of the main arm center of gravity from the main arm lower purchase point, 7. The method of calculating the force limit of a truck-mounted crane according to claim 6, characterized in that, The force arm of the main arm center of gravity is .

8. The method of calculating the load limit of a truck-mounted crane according to claim 1, characterized in that, The total weight force of the master arm system Equivalent weight force of the master arm, telescopic cylinder and wire rope, and its action point is dynamically determined by calibration fitting.

9. The method of claim 1, wherein, In the step S4, the force arm of the load with respect to the hook is equal to the force arm of the load with respect to the main arm lower point .

10. The method of calculating the load limit of a truck-mounted crane according to claim 1, characterized in that, The hook gravity Is a preset constant, or real-time acquisition through pressure sensor.

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