Robot arm lightweight design method for multiple optimization of rotational inertia

Abstract

The invention discloses a robot arm lightweight design method for rotational inertia multi-time optimization, and relates to the technical field of robot design, S1, the first rotational inertia is determined as a topological optimization constraint value of a target function; the rotational inertia of the robot arm is optimized and redesigned for multiple times, and a topological optimization model takes the minimum rotational inertia of the arm around the Z axis as a target function and takes strain energy and volume as constraints. The method has the following beneficial effects that the rotational inertia, the volume, the strain energy and the maximum stress all meet the requirements as design termination conditions, and if the conditions are not met, topological optimization and redesign which take the rotational inertia as an objective function and take the strain energy and the volume as constraints are carried out again on a redesign structure until all the termination conditions are met; the robot arm is subjected to topological optimization and redesign for many times, a reasonable structure is obtained, the rotational inertia of the robot arm finally reaches an ideal value, and the designed robot arm meets the requirements for light weight, rigidity and strength.

Description

Technical Field

[0001] The present invention relates to the technical field of robot design, and in particular to a lightweight design method for a robot arm with multiple optimizations of rotational inertia. Background Art

[0002] The lightweight development of robots is conducive to improving their mobility, speed, movement accuracy, work efficiency and endurance, and is an inevitable trend in industrial development. The lightweight of robots is mainly achieved from two aspects: materials and structure. Lightweight design is an important way to lightweight the structure of robots. It can not only reduce the weight of the robot body and optimize the structure, but also increase the flexibility of the robot and improve its maneuverability.

[0003] In addition to its weight, the most direct factor affecting the maneuverability, speed and accuracy of a robot is the moment of inertia of rotating parts such as the arm. The moment of inertia is a measure of the inertia of a rigid body when it rotates. The smaller the moment of inertia of a robot arm, the better its rotation flexibility and controllability, and the higher the control accuracy. How to meet the weight reduction requirements and achieve a more ideal moment of inertia of a robot arm while ensuring rigidity and strength is a complex optimization and design process.

[0004] Generally speaking, there is no direct correlation between the moment of inertia and volume of a robot arm. A smaller volume does not mean a smaller moment of inertia, and a reduction in volume will generally lead to a weakening of the structural stiffness and strength. Therefore, the optimization and design process needs to comprehensively consider the influence of the corresponding variables and find a more reasonable method to simultaneously meet the requirements of moment of inertia, weight, stiffness and strength. In addition, the most commonly used method for structural lightweight design is structural topology optimization. Structural topology optimization mainly seeks the optimal distribution of materials by removing materials. One optimization and design process may not necessarily produce ideal results. It is necessary to combine optimization and design and iterate repeatedly until the final goal is achieved. Therefore, a lightweight design method for a robot arm with multiple optimizations of moment of inertia is proposed. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a lightweight design method for a robot arm with multiple optimizations of the moment of inertia, which solves the problems raised in the above-mentioned background technology.

[0006] To achieve the above objectives, the present invention is implemented by the following technical solutions: a lightweight design method for a robot arm with multiple optimizations of the moment of inertia, comprising the following steps:

[0007] S1: The first moment of inertia is used as the topology optimization constraint value of the objective function;

[0008] The moment of inertia of the robot arm is topologically optimized and redesigned multiple times. The topology optimization model takes the minimum moment of inertia of the arm around the Z axis as the objective function, and takes strain energy and volume as constraints. The volume constraint value is set according to the weight reduction target. The strain energy constraint value to ensure stiffness must be set by estimation. Therefore, a topology optimization model with minimum strain energy as the objective function is first established. The model takes the moment of inertia around the Z axis and volume as constraints, and the volume constraint is set to less than 60% of the initial weight (the weight reduction target in this example is to require the overall structure to be reduced to less than 60% of the initial weight). The upper limit of the moment of inertia constraint is set 5% to 10% higher than the expected target value. After the topology optimization converges, the final optimized value of the strain energy is used as the upper limit of the strain energy constraint value of the first topology optimization with the moment of inertia as the objective function.

[0009] S2: Moment of inertia optimization and robot arm redesign process;

[0010] S21: The first topology optimization with moment of inertia as the objective function;

[0011] A topology optimization model was established. The objective function was to minimize the moment of inertia around the Z axis. The constraints were volume and strain energy. The volume constraint was still set to V≤0.6V0 (V0 initial volume), and the strain energy was set according to the final optimized value of the strain energy (10.68987751N.cm in this example), that is, strain energy≤10.69N.cm. The topology optimization converged after 35 design cycles, and the structure after the topology optimization material was deleted was obtained.

[0012] S22: 1st redesign;

[0013] The first redesign is performed in the material deleted area. The holes formed by the redesign can only be included in the material deleted area. Since the unit deletion is incomplete when removing materials by topology optimization, some holes are not fully penetrable. Therefore, the hole area formed by the redesign is smaller than the actual material deleted area, and the subtracted weight and moment of inertia are smaller than the optimized results.

[0014] In this example, it can be found in the Abaqus software that the first redesigned structure volume V1 is 1725.17 cm 3, accounting for 52.4% of the initial structure volume V0, and has reached the weight reduction target of less than 60%. In order to determine whether the moment of inertia, strain energy and maximum stress of the first redesigned structure meet the requirements, it is necessary to establish a topology optimization calculation model 1 to determine the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. The topology optimization calculation model 1 takes the first redesigned structure as the object, and takes the minimum moment of inertia around the Z axis as the objective function. The constraints are still volume and strain energy, and the volume constraint value is set to be less than or equal to the volume of the first redesigned structure. In this way, the variable values ​​and stress cloud diagrams of the topology optimization process completed by the calculation model in the 0th design cycle are maintained in the initial state without material deletion, which can reflect the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. Since the volume constraint plays a leading role in the 0th design cycle of the topology optimization calculation model, that is, the corresponding strain energy when the volume remains unchanged is also the strain energy value of the redesigned structure, which has little to do with the size of the strain energy constraint value, so the strain energy constraint value can be relatively relaxed. In this case, strain energy≤11.7N.cm (enlarged from 10.69N.cm). In this example, it can be obtained from the 0th design cycle that the moment of inertia of the first redesigned structure is 2515.04kg.cm 2 , strain energy is 9.7875N.cm, maximum stress is 103.2MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Next, a second topology optimization and redesign with the moment of inertia as the objective function is required;

[0015] S23: The second topology optimization with moment of inertia as the objective function;

[0016] The second topology optimization with moment of inertia as the objective function is based on the first redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis, and the constraints are volume and strain energy. Since the first redesigned structure has achieved the weight reduction goal, the volume constraint value can be set to be less than or equal to the initial volume value of the first redesigned structure, that is, V≤V1 (V1 is the initial volume of the first redesigned structure); and in this example, the strain energy of the first redesigned structure of 9.7875N.cm is less than the upper limit of the strain energy constraint value of 10.689N.cm in the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value in the second topology optimization with moment of inertia as the objective function can be increased by 10% to 15%, that is, it can be increased by 10% to 15% on the basis of 10.689N.cm to increase the optimization search space. In this example, strain energy≤11.8N.cm. The topology optimization converged after 31 design cycles, and the structure after the topology optimization deleted the material was obtained;

[0017] S24: 2nd redesign;

[0018] The material deletion area obtained in step S23 is redesigned for the second time. In this example, the volume V2 of the second redesigned structure can be found in the Abaqus software to be 1559.08 cm 2 , and continued to reduce to 47.35% of the initial structure volume V0. Topology optimization calculation model 2 was established to determine the magnitude of the second redesign structure moment of inertia, strain energy and maximum stress. The modeling method was the same as that of topology optimization calculation model 1. In this example, the second redesign structure moment of inertia was 2116.05kg.cm 2 , strain energy 10.53N.cm, the maximum stress is 208.9MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Next, a third topology optimization and redesign with the moment of inertia as the objective function is required;

[0019] S25: The third topology optimization with moment of inertia as the objective function;

[0020] The third topology optimization with moment of inertia as the objective function is based on the second redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis. The constraints are volume and strain energy. The volume constraint value is set to be less than or equal to the initial volume value of the second redesigned structure, that is, V≤V2 (V2 is the initial volume of the second redesigned structure). The strain energy of 10.53N.cm is not much different from the upper limit of the strain energy constraint value of 10.689N.cm of the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value of the third topology optimization with moment of inertia as the objective function should be kept at the level of the strain energy constraint value of the second topology optimization with moment of inertia as the objective function or only slightly adjusted. In this example, strain energy≤11.8N.cm is taken. The topology optimization converges after 26 design cycles, and the structure after the topology optimization deletes the material is obtained. After three topology optimizations, the material reduction is limited.

[0021] S26: 3rd redesign;

[0022] The material deletion area obtained in step S25 is redesigned for the third time. It can be checked in Abaqus software. The third redesigned structure volume V3 is 1540.78cm 3 , accounting for 46.79% of the initial structure volume V0. There is not much room for weight reduction. A topology optimization calculation model 3 is established to determine the moment of inertia, strain energy and maximum stress of the third redesigned structure. The modeling method is the same as that of topology optimization calculation models 1 and 2. The moment of inertia and strain energy as well as the maximum stress are obtained to meet the strength requirements, that is, the moment of inertia, strain energy, volume and maximum stress all meet the requirements, so the final design result is output.

[0023] Preferably, the first moment of inertia of the S1 is the topology optimization constraint value of the objective function. In this example, the moment of inertia of the initial structure around the Z axis is 6305.79 kg.cm 2 The expected goal is to reduce the initial structure moment of inertia to less than one third, that is, 2102kg.cm 2 The following is an increase of 5% to 10% in order to increase the search space for topology optimization and reduce the strain energy optimization value to ensure stiffness. The upper limit of the transmission inertia constraint value is set to 2265kg.cm 2 , i.e. J≤2265kg.cm 2 .

[0024] Preferably, in S1: Abaqus6.14 software is used to perform geometric modeling and optimization in the process of determining the topological optimization constraint value of the objective function for the first time, and the topological optimization converges after 37 design cycles. After convergence, the final optimized value of strain energy is 10.68987751N.cm, and the moment of inertia is 2261.6kg.cm 2 The volume is reduced to 0.49364 of the initial volume. The maximum stress is 49.22MPa, which meets the strength condition. If the optimal value of strain energy 10.68987751N.cm is used as the upper limit of the constraint for the subsequent first topology optimization with moment of inertia as the objective function, it provides support for the guarantee of rigidity and strength conditions.

[0025] Preferably, in S23: the structure after the topology optimization is deleted in the second topology optimization step with the moment of inertia as the objective function, the moment of inertia after optimization is 1677.25 kg.cm 2 , the strain energy is 11.789N.cm, and the volume reduction is 0.7532 of the initial volume of the first redesigned structure.

[0026] Preferably, in the S25: the moment of inertia after optimization in the third topology optimization process with the moment of inertia as the objective function is 1624.79 kg.cm 2 , the strain energy is 11.791N.cm, and the volume reduction is 0.8152 of the initial volume of the second redesigned structure.

[0027] Preferably, the S26: moment of inertia in the third redesign process is 2068.64 kg.cm 2 ≤2102kg.cm 2 , the strain energy is 10.6465N.cm≤10.689N.cm, and the maximum stress is 203.7MPa, which meets the strength requirements.

[0028] The present invention provides a lightweight design method for a robot arm with multiple optimization of the moment of inertia, which has the following beneficial effects:

[0029] This lightweight design method for a robot arm with multiple optimizations of the moment of inertia takes the moment of inertia as the objective function, volume and strain energy as constraints, and takes the moment of inertia, volume, strain energy and maximum stress all meeting the requirements as the design termination condition. If the conditions are not met, a topology optimization and redesign with the moment of inertia as the objective function and strain energy and volume as constraints are performed again on the redesigned structure until all termination conditions are met. By performing multiple topology optimizations and redesigns on the robot arm, a reasonable structure is obtained, so that the moment of inertia of the robot arm finally reaches an ideal value, and the designed robot arm meets the requirements of lightweight, stiffness and strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the lightweight design method for a robot arm with multiple optimizations of the moment of inertia according to the steps of the present invention;

[0031] Figure 2 This is the initial design structure diagram of the robot arm of the present invention;

[0032] Figure 3 It is the strain energy variation curve diagram of the present invention;

[0033] Figure 4 It is a graph of various variables of the topology optimization process observed in the Abaqus background monitor of the present invention;

[0034] Figure 5 It is a stress cloud diagram of the structure after the topology optimization of the present invention converges;

[0035] Figure 6 The first topology optimization process and variable value diagram with moment of inertia as the objective function observed in the monitor of the present invention;

[0036] Figure 7 This is the first topology optimization structure diagram of the present invention with the moment of inertia as the objective function;

[0037] Figure 8 This is the first redesign of the structural diagram of the present invention;

[0038] Fig. 9 It is a variable value diagram of the 0th design cycle of the first redesigned structural topology optimization calculation model 1 of the present invention;

[0039] Fig.10 This is the first redesign of the structural stress cloud diagram of the present invention;

[0040] Fig.11 The second topology optimization process with the moment of inertia as the objective function and the variable value diagram observed in the monitor of the present invention;

[0041] Fig.12 This is the second topology optimization structure diagram of the present invention with the moment of inertia as the objective function;

[0042] Fig.13 This is the second redesigned structural diagram of the present invention;

[0043] Fig.14 The variable diagram of the 0th design cycle of the second redesigned structural topology optimization calculation model 2 of the present invention;

[0044] Fig.15 The structural stress cloud diagram of the second redesign of the present invention;

[0045] Fig.16 It is the third topology optimization process and variable value diagram with moment of inertia as the objective function observed in the monitor of the present invention;

[0046] Fig.17 This is the third topology optimization structure diagram of the present invention with the moment of inertia as the objective function;

[0047] Fig.18 This is an enlarged view of the back of the topological optimization structure of the present invention for the third time with the moment of inertia as the objective function;

[0048] Fig.19 This is the third redesigned structural diagram of the present invention;

[0049] Fig. 20 It is a variable value diagram of the 0th design cycle of the third redesigned structural topology optimization calculation model of the present invention;

[0050] Fig.21 This is the third redesign of the structural stress cloud diagram of the present invention. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0052] The present invention provides a technical solution: a lightweight design method for a robot arm with multiple optimization of the moment of inertia, comprising the following steps:

[0053] Taking the design of a certain type of robot arm structure as an example, the initial design structure is as follows Figure 2 As shown, the arm can be moved around Figure 2 The z-axis rotates, and the relevant parameters of the robot arm are shown in Table 1;

[0054] Table 1. Parameters related to the initial design of the robot arm

[0055]

[0056]

[0057] In order to make the robot arm have a relatively ideal moment of inertia, while ensuring a certain rigidity and strength, and meeting the weight reduction requirements, it is planned to perform topological optimization on the initial design structure of the robot arm. The topological optimization objective function is to minimize the moment of inertia of the arm around the Z axis, and set relevant constraints at the same time. Too many constraints will cause the optimization process to not converge. Therefore, the constraint variables are set to strain energy and volume to ensure rigidity and meet the weight reduction requirements. Whether the strength requirements are met can be compared with the maximum stress value of each redesigned structure and the strength condition, and processed and guaranteed in accordance with the method of process 1;

[0058] S1: The first moment of inertia is used as the topology optimization constraint value of the objective function;

[0059] The moment of inertia of the robot arm was optimized and redesigned many times. The topology optimization model takes the minimum moment of inertia of the arm around the Z axis as the objective function, and takes strain energy and volume as constraints. The volume constraint value is set according to the weight reduction target. In this case, the overall structure is required to be reduced to less than 60% of the initial weight, that is, the volume constraint V≤0.6V0 (V0 initial design structure volume);

[0060] The strain energy constraint value to ensure stiffness must be set through estimation. First, a topology optimization model with minimum strain energy as the objective function is established. The model uses the moment of inertia and volume around the Z axis as constraints. The volume constraint is set to less than 60% of the initial weight, and the upper limit of the moment of inertia constraint is set 5% to 10% higher than the expected target value. After the topology optimization converges, the final optimized value of the strain energy is used as the upper limit of the strain energy constraint value of the first topology optimization with the moment of inertia as the objective function. The initial structure has a moment of inertia of 6305.79 kg.cm around the Z axis. 2 The expected goal is to reduce the initial structure moment of inertia to less than one third, that is, 2102kg.cm 2 The following is a 5% to 10% increase in order to increase the topology optimization search space and reduce the strain energy optimization value to ensure stiffness. However, it is not advisable to increase it too much. If it is increased too much, the strain energy constraint value will be too small in the subsequent optimization with the moment of inertia as the objective function, which will reduce the search space and make the optimization process difficult to converge. In this example, the upper limit of the moment of inertia constraint value is set to 2265kg.cm 2 , i.e. J≤2265kg.cm 2 ;

[0061] Abaqus6.14 software was used for geometric modeling and optimization. The topology optimization converged after 37 design cycles. Figure 3 , Figure 4 As shown, the optimal value of strain energy after convergence is 10.68987751N.cm, and the moment of inertia is 2261.6kg.cm2 , the volume is reduced to 0.49364 of the initial volume, and the corresponding stress cloud diagram is as follows Figure 5 , the maximum stress is 49.22MPa, which obviously meets the strength condition. If the optimal value of strain energy 10.68987751N.cm is used as the upper limit of the constraint in the subsequent first topology optimization with moment of inertia as the objective function, it provides support for the guarantee of rigidity and strength conditions;

[0062] S2: Moment of inertia optimization and robot arm redesign process;

[0063] S21: The first topology optimization with moment of inertia as the objective function;

[0064] First, a topology optimization model is established. The objective function is to minimize the moment of inertia around the Z axis. The constraints are volume and strain energy. The volume constraint is still set to V≤0.6V0 (V0 initial volume), and the strain energy is set according to the optimal value of the strain energy 10.68987751N.cm, that is, strain energy≤10.69N.cm. The topology optimization converges after 35 design cycles. Figure 6 , and the structure after topology optimization and material deletion is obtained, as Figure 7 ,from Figure 6 It can be seen that the moment of inertia after optimization is 1763.898kg.cm 2 , the strain energy is 10.635N.cm, and the volume is reduced to 0.40962 of the initial volume;

[0065] S22: 1st redesign;

[0066] exist Figure 7 The material deletion area is redesigned for the first time, and its structure is as follows Figure 8 The holes formed by the redesign can only be included in the material deletion area. Since the unit deletion is incomplete when removing materials by topology optimization, some holes are not fully penetrable. Therefore, the hole area formed by the redesign is smaller than the actual material deletion area, and the subtracted weight and moment of inertia are smaller than the optimized results.

[0067] It can be checked in Abaqus software that the first redesigned structure volume V1 is 1725.17cm 3, accounting for 52.4% of the initial structure volume V0, and has reached the weight reduction target of less than 60%. In order to determine whether the moment of inertia, strain energy and maximum stress of the first redesigned structure meet the requirements, it is necessary to establish a topology optimization calculation model 1 to determine the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. The topology optimization calculation model 1 takes the first redesigned structure as the object, and takes the minimum moment of inertia around the Z axis as the objective function. The constraints are still volume and strain energy, and the volume constraint value is set to be less than or equal to the volume of the first redesigned structure. In this way, the variable values ​​and stress cloud diagrams of the topology optimization process completed by this calculation model in the 0th design cycle are maintained in the initial state where the material is not deleted, which can reflect the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. Since the volume constraint plays a dominant role in the 0th design cycle of the topology optimization calculation model, that is, the corresponding strain energy when the volume remains unchanged is also the strain energy value of the redesigned structure, which has little to do with the size of the strain energy constraint value, the strain energy constraint value can be relatively relaxed, and strain energy≤11.7N.cm. Fig. 9 As shown, from the 0th design cycle, it can be obtained that the moment of inertia of the first redesigned structure is 2515.04kg.cm 2 , strain energy 9.7875N.cm, from Fig.10 The stress cloud diagram shows that the maximum stress is 103.2MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Below, according to Figure 1 The process requires a second topology optimization and redesign with the moment of inertia as the objective function;

[0068] S23: The second topology optimization with moment of inertia as the objective function;

[0069] The second topology optimization with moment of inertia as the objective function is based on the first redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis. The constraints are volume and strain energy. Since the first redesigned structure has achieved the weight reduction goal, the volume constraint value can be set to be less than or equal to the initial volume value of the first redesigned structure, that is, V≤V1 (V1 is the initial volume of the first redesigned structure); and the strain energy of the first redesigned structure, 9.7875N.cm, is less than the upper limit of the strain energy constraint value of 10.689N.cm in the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value in the second topology optimization with moment of inertia as the objective function can be increased by 10% to 15%, that is, it can be increased by 10% to 15% on the basis of 10.689N.cm to increase the optimization search space, and the strain energy is taken as ≤11.8N.cm. The topology optimization converged after 31 design cycles, as shown in Fig.11 , and the structure after topology optimization and material deletion is obtained, as Fig.12 .from Fig.11 It can be seen that the moment of inertia after optimization is 1677.25kg.cm 2 , the strain energy is 11.789N.cm, and the volume reduction is 0.7532 of the initial volume of the first redesigned structure;

[0070] S24: 2nd redesign;

[0071] exist Fig.12 The material deletion area is redesigned for the second time, and its structure is as follows Fig.13 In Abaqus software, it can be found that the second redesigned structure volume V2 is 1559.08 cm 3 , and continued to reduce to 47.35% of the initial structure volume V0. Topology optimization calculation model 2 was established to determine the magnitude of the second redesign structure moment of inertia, strain energy and maximum stress. The modeling method was the same as that of topology optimization calculation model 1. Fig.14 It can be obtained that the moment of inertia of the second redesigned structure is 2116.05kg.cm 2 , strain energy 10.53N.cm, from Fig.15 The stress cloud diagram shows that the maximum stress is 208.9MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Below, according to Figure 1 The process requires a third topology optimization and redesign with the moment of inertia as the objective function;

[0072] S25: The third topology optimization with moment of inertia as the objective function;

[0073] The third topology optimization with moment of inertia as the objective function is based on the second redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis. The constraints are volume and strain energy. The volume constraint value is set to be less than or equal to the initial volume value of the second redesigned structure, that is, V≤V2 (V2 is the initial volume of the second redesigned structure); and the strain energy of 10.53N.cm is not much different from the upper limit of the strain energy constraint value of 10.689N.cm of the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value of the third topology optimization with moment of inertia as the objective function should be kept at the level of the strain energy constraint value of the second topology optimization with moment of inertia as the objective function or only slightly adjusted, taking strain energy≤11.8N.cm. The topology optimization converged after 26 design cycles, as shown in Figure 2. Fig.16 , and the structure after topology optimization and material deletion is obtained, as Fig.17 and Fig.18 After three topology optimizations, the material reduction is limited. Fig.16 It can be seen that the moment of inertia after optimization is 1624.79kg.cm2 , the strain energy is 11.791N.cm, and the volume reduction is 0.8152 of the initial volume of the second redesigned structure;

[0074] S26: 3rd redesign;

[0075] exist Fig.17 The material deletion area is redesigned for the third time, and its structure is as follows Fig.19 In Abaqus software, it can be found that the third redesigned structure volume V3 is 1540.78cm 3 , accounting for 46.79% of the initial structure volume V0, there is not much room for weight reduction. Topology optimization calculation model 3 is established to determine the magnitude of the moment of inertia, strain energy and maximum stress of the third redesign structure. The modeling method is the same as that of topology optimization calculation models 1 and 2. Fig. 20 It can be obtained that the moment of inertia of the third redesigned structure is 2068.64kg.cm 2 ≤2102kg.cm 2 , strain energy 10.6465N.cm≤10.689N.cm, from Fig.15 From the stress cloud diagram, we can see that the maximum stress is 203.7MPa, which meets the strength requirements, that is, the moment of inertia, strain energy, volume and maximum stress all meet the requirements. Therefore, the final design result is output as follows: Fig.19 .

[0076] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A lightweight design method for a robot arm with multiple optimizations of moment of inertia, characterized by: The following steps are involved: S1: The first moment of inertia is used as the topology optimization constraint value of the objective function; The moment of inertia of the robot arm is topologically optimized and redesigned many times. The topology optimization model takes the minimum moment of inertia of the arm around the Z axis as the objective function, and takes strain energy and volume as constraints. The volume constraint value is set according to the weight reduction target. The strain energy constraint value to ensure stiffness must be set by estimation. Therefore, a topology optimization model with minimum strain energy as the objective function is first established. The model takes the moment of inertia around the Z axis and volume as constraints, and the volume constraint is set to less than 60% of the initial weight. In this example, the weight reduction target is to reduce the overall structure to less than 60% of the initial weight. The upper limit of the moment of inertia constraint is set 5% to 10% higher than the expected target value. After the topology optimization converges, the final optimized value of the strain energy is used as the upper limit of the strain energy constraint value of the first topology optimization with the moment of inertia as the objective function. S2: Moment of inertia optimization and robot arm redesign process; S21: The first topology optimization with moment of inertia as the objective function; A topology optimization model is established. The objective function is to minimize the moment of inertia around the Z axis. The constraints are volume and strain energy. The volume constraint is still set to V≤0.6V0 (V0 initial volume), and the strain energy is set according to the final optimization value of the strain energy mentioned above, which is 10.68987751N.cm in this case, that is, strain energy≤10.69N.cm. The topology optimization converges after 35 design cycles, and the structure after the topology optimization material is deleted is obtained. S22: 1st redesign; The first redesign is performed in the material deleted area. The holes formed by the redesign can only be included in the material deleted area. Since the unit deletion is incomplete when removing materials by topology optimization, some holes are not fully penetrable. Therefore, the hole area formed by the redesign is smaller than the actual material deleted area, and the subtracted weight and moment of inertia are smaller than the optimized results. In this example, it can be found in the Abaqus software that the first redesigned structure volume V1 is 1725.17 cm 3 , accounting for 52.4% of the initial structure volume V0, and has reached the weight reduction target of less than 60%. In order to determine whether the moment of inertia, strain energy and maximum stress of the first redesigned structure meet the requirements, it is necessary to establish a topology optimization calculation model 1 to determine the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. The topology optimization calculation model 1 takes the first redesigned structure as the object, and takes the minimum moment of inertia around the Z axis as the objective function. The constraints are still volume and strain energy, and the volume constraint value is set to be less than or equal to the volume of the first redesigned structure. In this way, the variable values ​​and stress cloud diagrams of the topology optimization process completed by the calculation model in the 0th design cycle are maintained in the initial state without material deletion, which can reflect the magnitude of the moment of inertia, strain energy and maximum stress of the first redesigned structure. Since the volume constraint plays a leading role in the 0th design cycle of the topology optimization calculation model, that is, the corresponding strain energy when the volume remains unchanged is also the strain energy value of the redesigned structure, which has little to do with the size of the strain energy constraint value, so the strain energy constraint value can be relatively relaxed. In this case, strain energy≤11.7N.cm, which is enlarged based on 10.69N.cm. From the 0th design cycle, it can be obtained that the moment of inertia of the first redesigned structure is 2515.04kg.cm 2 , strain energy is 9.7875N.cm, maximum stress is 103.2MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Next, a second topology optimization and redesign with the moment of inertia as the objective function is required; S23: The second topology optimization with moment of inertia as the objective function; The second topology optimization with moment of inertia as the objective function is based on the first redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis, and the constraints are volume and strain energy. Since the first redesigned structure has achieved the weight reduction goal, the volume constraint value can be set to be less than or equal to the initial volume value of the first redesigned structure, that is, V≤V1 (V1 is the initial volume of the first redesigned structure); and in this example, the strain energy of the first redesigned structure of 9.7875N.cm is less than the upper limit of the strain energy constraint value of 10.689N.cm in the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value in the second topology optimization with moment of inertia as the objective function can be increased by 10% to 15%, that is, it can be increased by 10% to 15% on the basis of 10.689N.cm to increase the optimization search space. In this example, strain energy≤11.8N.cm. The topology optimization converged after 31 design cycles, and the structure after the topology optimization deleted the material was obtained; S24: 2nd redesign; The material deletion area obtained in step S23 is redesigned for the second time. In this example, the volume V2 of the second redesigned structure can be found in the Abaqus software to be 1559.08 cm 3 , and continued to reduce to 47.35% of the initial structure volume V0. Topology optimization calculation model 2 was established to determine the magnitude of the second redesign structure moment of inertia, strain energy and maximum stress. The modeling method was the same as that of topology optimization calculation model 1. In this example, the second redesign structure moment of inertia was 2116.05kg.cm 2 , strain energy 10.53N.cm, the maximum stress is 208.9MPa, which meets the strength requirements, but the moment of inertia does not reach the expected target value of 2102kg.cm 2 Next, a third topology optimization and redesign with the moment of inertia as the objective function is required; S25: The third topology optimization with moment of inertia as the objective function; The third topology optimization with moment of inertia as the objective function is based on the second redesigned structure as the optimization object. The objective function is to minimize the moment of inertia of the structure around the Z axis. The constraints are volume and strain energy. The volume constraint value is set to be less than or equal to the initial volume value of the second redesigned structure, that is, V≤V2 (V2 is the initial volume of the second redesigned structure). The strain energy of 10.53N.cm is not much different from the upper limit of the strain energy constraint value of 10.689N.cm of the first topology optimization with moment of inertia as the objective function. Therefore, the strain energy constraint value of the third topology optimization with moment of inertia as the objective function should be kept at the level of the strain energy constraint value of the second topology optimization with moment of inertia as the objective function or only slightly adjusted. In this example, strain energy≤11.8N.cm is taken. The topology optimization converges after 26 design cycles, and the structure after the topology optimization deletes the material is obtained. After three topology optimizations, the material reduction is limited. S26: 3rd redesign; The material deletion area obtained in step S25 is redesigned for the third time. It can be checked in Abaqus software. The third redesigned structure volume V3 is 1540.78cm 3 , accounting for 46.79% of the initial structure volume V0. There is not much room for weight reduction. A topology optimization calculation model 3 is established to determine the moment of inertia, strain energy and maximum stress of the third redesigned structure. The modeling method is the same as that of topology optimization calculation models 1 and 2. The moment of inertia and strain energy as well as the maximum stress are obtained to meet the strength requirements, that is, the moment of inertia, strain energy, volume and maximum stress all meet the requirements, so the final design result is output.

2. The method for lightweight design of a robot arm for multiple optimization of moment of inertia according to claim 1 is characterized in that: S1: The first moment of inertia is the topology optimization constraint value of the objective function. In this process, the initial structure's moment of inertia around the Z axis is 6305.79 kg.cm 2 The expected goal is to reduce the initial structure moment of inertia to less than one third, that is, 2102kg.cm 2 The following is an increase of 5% to 10% to increase the topology optimization search space and reduce the strain energy optimization value to ensure stiffness. The upper limit of the moment of inertia constraint value is set to 2265kg.cm 2 , i.e. J≤2265kg.cm 2 .

3. The method for lightweight design of a robot arm for multiple optimization of moment of inertia according to claim 1 is characterized in that: S1: In the process of determining the topology optimization constraint value of the first moment of inertia as the objective function, Abaqus6.14 software was used for geometric modeling and optimization. The topology optimization converged after 37 design cycles. After convergence, the optimal value of strain energy was 10.68987751N.cm and the moment of inertia was 2261.6kg.cm 2 The volume is reduced to 0.49364 of the initial volume. The maximum stress is 49.22MPa, which meets the strength condition. If the optimal value of strain energy 10.68987751N.cm is used as the upper limit of the constraint for the subsequent first topology optimization with moment of inertia as the objective function, it provides support for the guarantee of rigidity and strength conditions.

4. The lightweight design method for a robot arm with multiple optimization of moment of inertia according to claim 1 is characterized in that: S23: The structure after the topology optimization material is deleted in the second topology optimization step with the moment of inertia as the objective function. The moment of inertia after optimization is 1677.25 kg.cm 2 , the strain energy is 11.789N.cm, and the volume reduction is 0.7532 of the initial volume of the first redesigned structure.

5. The method for lightweight design of a robot arm for multiple optimization of moment of inertia according to claim 1, characterized in that: S25: The moment of inertia after optimization in the third topology optimization process with the moment of inertia as the objective function is 1624.79 kg.cm 2 , the strain energy is 11.791N.cm, and the volume reduction is 0.8152 of the initial volume of the second redesigned structure.

6. The method for lightweight design of a robot arm for multiple optimization of moment of inertia according to claim 1, characterized in that: S26: The moment of inertia in the third redesign process is 2068.64 kg.cm 2 ≤2102kg.cm 2 , the strain energy is 10.6465N.cm≤10.689N.cm, and the maximum stress is 203.7MPa, which meets the strength requirements.

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