A design method for robot arm reinforcement

Abstract

The invention discloses a design method for reinforcing ribs of a robot boom, which is applicable to a bending boom with a three-axis motor placed at the rear and a two-axis motor directly connected to a reducer. For a boom without reinforcing ribs, stress analysis and displacement analysis are performed through finite element analysis under extreme working conditions to obtain stress and displacement cloud maps of the boom model. Image recognition is used to remove the main displacement isolines of the displacement cloud map, and reinforcing ribs are established in the direction of the modified line and in a vertical direction. The position, direction and size of the reinforcing ribs can be quickly obtained. The obtained reinforcing ribs can not only achieve a balance between compact structure and non-interference layout, but also effectively increase the strength of the boom, improve the overall rigidity of the robot, and thus improve the machine precision.

Description

Technical Field

[0001] The invention belongs to the field of robot arm design, and in particular relates to a design method for a robot arm reinforcement rib. Background Art

[0002] Regarding the design of the arms of micro and small industrial robots, the arm span of small robots is usually small and the structure is too compact, so a reasonable layout is required to prevent interference, difficulty in internal routing, and limited operating angles. Since small robots are usually set with a smaller wall thickness to achieve lightweight, their strength will be greatly reduced, and the load that the connecting surface of the arm can withstand is limited. In order to increase the strength of the joint surface, it is necessary to add a reinforcing plate, commonly known as a reinforcing rib, on the common vertical surface of the two combined bodies.

[0003] Arranging stiffeners is one of the common means to improve the mechanical properties of structures. It has been widely used in various equipment structures. It is of great significance to quickly and effectively design the distribution of stiffeners to maximize the mechanical properties of structures. At present, a variety of stiffener distribution optimization design methods have been effectively applied, mainly divided into structural topology optimization methods based on unit density and distribution optimization methods based on base structure method. The stiffener distribution morphology obtained by the former is not clear enough, and further post-processing is required to obtain the true stiffener distribution, and the optimality of the stiffener distribution after post-processing cannot be guaranteed; the result obtained by the latter has a clear stiffener distribution configuration, but due to the limitations of the geometric characteristics of the base structure, the stiffeners have specific distribution angles, such as 0°, 45°, 90°, and 135°, and the design freedom is limited. Summary of the invention

[0004] The purpose of the present invention is to provide a design method for robot boom reinforcement ribs, so that the designed reinforcement ribs can effectively increase the strength of the boom, improve the overall rigidity of the robot, and make the boom structure compact and the layout reasonable without interference.

[0005] The present invention provides a design method for reinforcing ribs of a robot arm, which is applicable to a bending type arm with a three-axis motor placed at the rear and a two-axis motor directly connected to a reducer, and comprises the following steps:

[0006] Step 1: Basic structural design of the boom

[0007] The two-axis motor and the reducer on the bending type arm are concentrically arranged. The common axis of the two-axis motor and the reducer is called the two-axis axis. Assuming that the axis of the two-axis and the axis of the three-axis motor are on the same vertical line, the axis of the three-axis motor, the three-axis reducer and the two-axis axis form a triangle.

[0008] Step 2: Finite element simulation of extreme conditions

[0009] After the basic structural design of the boom is completed, the strength of the boom without reinforcement ribs is checked by finite element analysis, that is, by performing stress analysis and displacement analysis on the boom under extreme working conditions, its force condition is judged, and the weak position of the structure or the position that needs to be strengthened is obtained; the boundary conditions applied for the strength check are the working condition and position with the maximum load. When the axis of the second axis is horizontal with the axis of the third axis reducer, the gravity and load torque are the largest;

[0010] In the stress analysis, if excessive stress is found, return to step 1 to add a structure to the basic structure of the boom to reduce the impact of concentrated stress, and / or increase the thickness of some locations with high stress;

[0011] In the displacement analysis, if the basic structural rigidity of the boom is insufficient, it is necessary to set reinforcing ribs on the boom to increase the bending resistance and proceed to step 3;

[0012] Step 3: Determine the position of the reinforcement

[0013] For the bending type boom, a reinforcing rib is set in the middle of the two sections of the folding line structure, that is, between the three-axis motor and the three-axis reducer. The specific position will be determined in the subsequent steps in combination with the boom structure space, processing technology, and appearance;

[0014] Step 4: Determine the direction of the reinforcement

[0015] (1) Post-processing of the displacement cloud map of the finite element analysis in step 2, displaying the plane displacement cloud map on the main view of the boom under the extreme working condition in the post-processing;

[0016] (2) After the displacement cloud map is obtained through post-processing, the main equal displacement boundary line is identified through the image. This line is the part of the boom that has the same displacement under this working condition. Referring to the position of the reinforcement rib determined in step 3, the main boundary line is selected, and its angle is extracted to obtain the first angle;

[0017] (3) Add at least a second reinforcement in the shear direction of the first reinforcement;

[0018] Step 5: Calculate the size of the reinforcement

[0019] After determining the direction and position of the reinforcement, the new structure of the boom after adding the reinforcement is obtained. Based on the post-processing of the displacement cloud map of the finite element analysis in step 2, the shear stress cloud map is displayed in the post-processing to display the local shear stress of the reinforcement, and the shear stress τ at the position of the reinforcement is obtained; at the same time, since the forces on the boom include its own gravity, the gravity of the reducer and subsequent structures, and the inertia force contained in the subsequent movement, the equivalent effect of these forces on the boom is equivalent to a torque around the axis of the two axes of the boom. The two-axis motor applies a counter torque of this equivalent effect to this part to make the boom reach a balanced state. The counter torque ∑M applied by the two-axis motor to this part is calculated as described in the following formula:

[0020] ∑M=F1L1+GL2=F2L(1)

[0021] In the formula, F1 is the equivalent load force of the three-axis reducer and subsequent components, and L1 is its lever arm; G is gravity, and L2 is its lever arm; F2 is the equivalent force of the big arm movement acting on the rib position by the counter torque, and L is the length of the lever arm at the rib position;

[0022] From the above formula, the equivalent force of the upper arm motion is:

[0023]

[0024] The equivalent support force is the equivalent force F2 of the arm motion, and its action point is selected at the position where the reinforcement ribs can be added;

[0025] The cross-sectional area of ​​the designed reinforcement should meet the following constraints:

[0026]

[0027] Where τ is the shear stress and A is the designed rib cross-sectional area;

[0028] The cross-sectional area of ​​the designed reinforcement is obtained by adjusting according to formula (3), and then the length and width of the reinforcement are selected according to the cross-sectional area. When the torsional force in the actual working condition is greater than that in the limit working condition, the tensile height of the reinforcement is increased as much as possible;

[0029] Step 6: Perform strength check on the boom with reinforcement ribs by finite element analysis to check whether its stress and displacement are improved. If it still cannot meet the use requirements, return to step 1 to redesign the basic structure of the boom until the strength of the boom meets the use requirements.

[0030] The adding of the second reinforcing rib in the shear direction of the first reinforcing rib means that the second reinforcing rib is perpendicular to the first reinforcing rib, and the second angle is the first angle plus 90 degrees.

[0031] After adding the second reinforcing rib, other reinforcing ribs that can locally increase the shear resistance are added alternately with the first reinforcing rib, taking into account whether the spatial layout is sufficient, the need for actual strength verification, the aesthetic layout or the convenience of processing.

[0032] The width and height of the reinforcing rib are greater than the wall thickness of the upper arm body.

[0033] By adopting the technical solution of the present invention, stress analysis and displacement analysis are performed on a boom without reinforcement ribs under extreme working conditions through finite element analysis, and stress and displacement cloud maps of the boom model are obtained. Image recognition is used to remove the main displacement isolines of the displacement cloud map, and reinforcement ribs are established in the direction of the displacement isolines and in the vertical direction. The position, direction and size of the reinforcement ribs can be quickly obtained. The obtained reinforcement ribs can not only achieve a balance between compact structure and non-interference layout, but also effectively increase the strength of the boom and improve the overall rigidity of the robot, thereby improving the machine precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a design flow chart of the present invention;

[0035] Figure 2 It is a load calculation schematic diagram of the present invention;

[0036] Figure 3 It is the displacement cloud diagram of the finite element analysis of the upper arm of the present invention;

[0037] Figure 4 It is a schematic diagram of the design of the upper arm reinforcement rib of the present invention.

[0038] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0039] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, and the embodiments described are only a part of the embodiments of the present invention, rather than all embodiments. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] The invention discloses a design method for reinforcing ribs of a robot arm, which is applicable to a bending type arm with a three-axis motor placed at the rear and a two-axis motor directly connected to a reducer.

[0041] Determining the main dimensions of the boom according to actual needs and designing the basic structure of the boom are not the protection content of the present invention. The present invention is to design the reinforcing ribs for the bending boom after the shape determination is completed. The two-axis motor and the reducer on the bending boom are concentrically arranged, and the common axis of the two-axis motor and the reducer is called the two-axis axis. Assuming that the axis of the two-axis and the axis of the three-axis motor are on the same vertical line, the axis of the three-axis motor, the three-axis reducer and the two-axis axis form a triangle.

[0042] After the basic structural design is completed, the main parts of the boom need to be checked for strength, and the weak structures or other key positions need to be strengthened. Usually, the boom is subjected to finite element simulation analysis, and its stress condition is determined by performing stress analysis and displacement analysis on the boom under extreme working conditions.

[0043] like Figure 3 As shown in the figure, the forces acting on the arm include its own gravity, the gravity of the reducer and subsequent structures, and the inertia force contained in the subsequent movement. The equivalent effect of these forces on the arm is equivalent to a torque around the axis of the two axes of the arm. The two-axis motor applies this counter torque to this part to make the arm reach a balanced state. Since the robot is in actual operation, both the speed and the mass matrix (center of gravity position) are constantly changing, so the boundary conditions applied for strength verification should be the working conditions and positions with the largest load. For the arm, when the axis positions of the two-axis reducer and the three-axis reducer are horizontal, the gravity and load torque are the largest.

[0044] The stress analysis mentioned above means that for places where stress is too high, we should first consider adding fillets, optimizing structural curves, etc. to reduce the impact of concentrated stress, and increase the strength of some places where stress is relatively high by increasing the thickness, etc.

[0045] The displacement analysis means that the force on the upper arm is similar to that on the cantilever beam structure, and the main reason for its displacement is the insufficient structural rigidity. Therefore, it is generally necessary to set reinforcing ribs at the upper joint of the upper arm to increase the bending resistance.

[0046] The reinforcement ribs of the bending type boom should be in the middle part of its two sections of the fold line structure. The structure of the bending type boom itself is designed based on the small arm span, and the space is small. The three-axis motor in the boom is generally set at the middle node. In order to ensure a lower center of gravity during the operation of the robot, the distance from the axis of the second-axis motor to the axis of the third-axis motor of the bending type boom is usually very small, and the distance from the axis of the third-axis motor to the axis of the three-axis reducer is relatively large. The position with the greatest force is also mainly the position of the three-axis reducer. Therefore, the reinforcement ribs are generally set between the three-axis motor and the three-axis reducer. The specific position can be determined by yourself based on the structure, processing technology, appearance, etc.

[0047] Usually, the reinforcement ribs on the straight arm of the robot are generally M-shaped or cross-shaped. However, through analysis and testing, it is found that the design of the M-shaped reinforcement ribs on the bending arm is different from that of the straight type. The straight arm is usually in a vertical state, and the strength requirements can be guaranteed by ensuring that the reinforcement ribs are horizontal and vertical. However, for the bending arm, due to the maximum force state, the force on the arm has a certain deviation angle with the vertical direction, which will weaken the effect of the reinforcement ribs to a certain extent.

[0048] like Figure 1 As shown, a design method for a robot arm reinforcement rib of the present invention specifically comprises the following steps:

[0049] Step 1: Basic structural design of the boom

[0050] The two-axis motor and the reducer on the bending type arm are concentrically arranged. The common axis of the two-axis motor and the reducer is called the two-axis axis. Assuming that the axis of the two-axis and the axis of the three-axis motor are on the same vertical line, the axis of the three-axis motor, the three-axis reducer and the two-axis axis form a triangle.

[0051] Step 2: Finite element simulation of extreme conditions

[0052] After the basic structural design of the boom is completed, the strength of the boom without reinforcement ribs is checked through finite element analysis, that is, by performing stress analysis and displacement analysis on the boom under extreme working conditions, its force condition is judged, so that the weak structure or other key positions can be strengthened. The boundary conditions imposed by the strength check are the working conditions and positions with the largest load. When the axis of the second axis is horizontal with the axis of the third axis reducer, the gravity and load torque are the largest.

[0053] In the stress analysis, if the stress is too high, return to step 1 to reduce the influence of concentrated stress by adding fillets, optimizing the structural curve, etc. to the basic structure of the boom, and / or increase the strength of some locations with high stress by increasing the thickness, etc.;

[0054] In the displacement analysis, it is considered that the basic structural rigidity of the boom is insufficient, so it is necessary to set reinforcing ribs on the boom to increase the bending resistance, and proceed to step 3;

[0055] Step 3: Determine the position of the reinforcement

[0056] For the bending type boom, a reinforcing rib is set in the middle of the two sections of the folding line structure, that is, between the three-axis motor and the three-axis reducer. The specific position will be determined in the subsequent steps in combination with the boom structure space, processing technology, appearance, etc.

[0057] Step 4: Determine the direction of the reinforcement

[0058] (1) Post-processing of displacement cloud diagram based on finite element analysis in step 2

[0059] Since the displacement of the boom is mainly caused by the lack of boom stiffness, the design of the reinforcement ribs is mainly to suppress the existing displacement. The plane displacement cloud diagram on the main view of the boom under the extreme working condition is displayed in the post-processing, such as Figure 3 As shown;

[0060] (2) After the displacement cloud map is obtained through post-processing, the main equal displacement boundary line is identified through the image. This line is the part of the boom that has the same displacement under this working condition. Referring to the position of the reinforcement rib determined in step 3, the main boundary line is selected, and its angle is extracted to obtain the first angle;

[0061] (3) Since the above design is only for extreme working conditions, the direction of the force is constantly changing during the design operation. Therefore, in addition to the first angle determined above, at least one reinforcement rib in other directions should be added to the direction of the big arm reinforcement rib. Since the reinforcement rib is mainly subjected to shear (perpendicular to the direction of the rib), adding reinforcement ribs in the shear direction will enhance its shear resistance. Therefore, vertical ribs are generally selected, that is, the second reinforcement rib is perpendicular to the first reinforcement rib, and the second angle is the first angle plus 90 degrees. However, there are other angles. Considering factors such as compact space, beautiful layout or convenient processing, as long as there are other reinforcement ribs staggered with the first reinforcement rib, its shear resistance can be partially increased; as for other additional reinforcement ribs, it depends on whether the space layout is sufficient and whether the actual strength verification is necessary, and they can be added as appropriate according to the above ideas;

[0062] Step 5: Calculate the size of the reinforcement

[0063] After determining the direction and position of the reinforcement, the new structure of the boom after adding the reinforcement is obtained. Based on the post-processing of the displacement cloud map of the finite element analysis in step 2, the shear stress cloud map is displayed in the post-processing to display the local shear stress of the reinforcement, and the shear stress τ at the position of the reinforcement is obtained; at the same time, since the forces on the boom include its own gravity, the gravity of the reducer and subsequent structures, and the inertia force contained in the subsequent movement, the equivalent effect of these forces on the boom is equivalent to a torque around the axis of the two axes of the boom. The two-axis motor applies a counter torque of this equivalent effect to this part to make the boom reach a balanced state. The counter torque ∑M applied by the two-axis motor to this part is calculated as described in the following formula:

[0064] ∑M=F1L1+GL2=F2L(1)

[0065] In the formula, F1 is the equivalent load force of the three-axis reducer and subsequent components, and L1 is its lever arm; G is gravity, and L2 is its lever arm; F2 is the equivalent force of the big arm movement acting on the rib position by the counter torque, and L is the length of the lever arm at the rib position;

[0066] From the above formula, the equivalent force of the upper arm movement is:

[0067]

[0068] The equivalent support force is the equivalent force F2 of the arm motion, and its action point is selected at the position where the reinforcement ribs can be added;

[0069] The cross-sectional area of ​​the designed reinforcement should meet the following constraints:

[0070]

[0071] Where τ is the shear stress and A is the designed rib cross-sectional area;

[0072] The cross-sectional area of ​​the designed reinforcement is obtained by adjusting according to formula (3), and then the length and width of the reinforcement are selected according to the cross-sectional area. For the case where the torsional force in the actual working condition is greater than the limit working condition, the tensile height of the reinforcement is increased as much as possible. Because it is impossible to determine the tensile height based on the shear resistance alone, the tensile height is given by experience based on the space for arranging the reinforcement. The large reinforcement can be wider and the small reinforcement can be narrower. The above-mentioned torsional force is combined with the actual working condition, considering the cantilever state of the boom, that is, one end is fixed and the other end is twisted, and the reinforcement is set thicker (higher); the cross-sectional area of ​​the reinforcement satisfies the above constraints to basically meet the use requirements. Usually, the strength of the reinforcement itself is higher than that of the boom body, so the width and height of the reinforcement are usually greater than the wall thickness of the boom body;

[0073] Step 6. Perform strength check on the boom with reinforcement ribs through finite element analysis to check whether its stress and displacement are improved. If it still cannot meet the use requirements, it means that its insufficient strength is likely due to insufficient structural design of the boom itself. Return to step 1 to redesign the basic structure of the boom until the strength of the boom meets the use requirements.

[0074] [Example] Take the design idea of ​​a small arm span six-axis robot as an example to verify the rationality of the above design method:

[0075] The specific implementation methods of steps 1, 2, and 3 can be carried out by conventional means or general methods, and will not be repeated here;

[0076] For step 4, Figure 3 As shown in the figure, the displacement cloud diagram of the reinforcement ribs shows approximately parallel equal displacement lines, and the angle between them and the horizontal position is about 60 degrees. Therefore, the first angle of the reinforcement ribs is designed to be 60 degrees and the second angle is 150 degrees. Figure 4 shown.

[0077] For step 5, the equivalent moment is 58.37Nm, the arm length at the reinforcing rib is 0.133m, and the shear stress is 13Mpa.

[0078]

[0079] The added reinforcement rib is 11mm high and 8mm wide, so the cross-sectional area A of the reinforcement rib is 88mm 2 , greater than the constraint condition 33.8mm 2 ;

[0080] For step 6, after re-finite element analysis of the upper arm with reinforcement ribs, its maximum displacement was reduced from 0.05mm to 0.028mm. It can be seen that the added reinforcement ribs effectively enhanced the strength of the upper arm.

[0081] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-restrictive from any point of view, and the scope of the invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates. Furthermore, it is apparent that the word "comprise" does not exclude other elements or, and the singular does not exclude the plural.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A design method for reinforcing ribs of a robot arm, applicable to a bending arm with a three-axis motor at the rear and a two-axis motor directly connected to a reducer, characterized in that The steps include: Step 1: Basic structural design of the boom The two-axis motor and the reducer on the bending type arm are concentrically arranged. The common axis of the two-axis motor and the reducer is called the two-axis axis. Assuming that the axis of the two-axis and the axis of the three-axis motor are on the same vertical line, the axis of the three-axis motor, the three-axis reducer and the two-axis axis form a triangle. Step 2: Finite element simulation of extreme conditions After the basic structural design of the boom is completed, the strength of the boom without reinforcement ribs is checked by finite element analysis, that is, by performing stress analysis and displacement analysis on the boom under extreme working conditions, its force condition is judged, and the weak position of the structure or the position that needs to be strengthened is obtained; the boundary conditions applied for the strength check are the working condition and position with the maximum load. When the axis of the second axis is horizontal with the axis of the third axis reducer, the gravity and load torque are the largest; In the stress analysis, if excessive stress is found, return to step 1 to add a structure to the basic structure of the boom to reduce the impact of concentrated stress, and / or increase the thickness of some locations with high stress; In the displacement analysis, if the basic structural rigidity of the boom is insufficient, it is necessary to set reinforcing ribs on the boom to increase the bending resistance and proceed to step 3; Step 3: Determine the position of the reinforcement For the bending type boom, a reinforcing rib is set in the middle of the two sections of the folding line structure, that is, between the three-axis motor and the three-axis reducer. The specific position will be determined in the subsequent steps in combination with the boom structure space, processing technology, and appearance; Step 4: Determine the direction of the reinforcement (1) Post-processing of the displacement cloud map based on the finite element analysis in step 2, displaying the plane displacement cloud map on the main view of the boom under the extreme working condition in the post-processing; (2) After obtaining the displacement cloud map through post-processing, the main equal displacement boundary line is identified through the image. This line is the part of the boom that has the same displacement under this working condition. Referring to the position of the reinforcement rib determined in step 3, the main equal displacement boundary line is selected, and its angle is extracted to obtain the first angle; (3) Add at least a second reinforcement in the shear direction of the first reinforcement; Step 5: Calculate the size of the reinforcement After determining the direction and position of the reinforcement rib, the new structure of the boom after adding the reinforcement rib is obtained. Based on the post-processing of the displacement cloud map of the finite element analysis in step 2, the shear stress cloud map is displayed in the post-processing to display the local shear stress of the reinforcement rib, and the shear stress at the reinforcement rib position is obtained. At the same time, since the forces acting on the boom include its own gravity, the gravity of the reducer and subsequent structures, and the inertia force contained in the subsequent movement, the equivalent force of these forces on the boom is equivalent to a torque around the axis of the two axes of the boom. The two-axis motor applies a counter torque of this equal force to this part to make the boom reach a balanced state. Formula (1) is used to calculate the counter torque of this equal force applied by the two-axis motor to this part. : （1） In the formula, is the equivalent load force of the three-axis reducer and subsequent components, For its force arm; G is gravity, For its force arm; is the equivalent force of the big arm motion acting on the stiffener position due to the reaction moment, and L is the length of the force arm at the stiffener position; From formula (1), the equivalent force of the upper arm motion is: （2） The equivalent support force is the equivalent force of the upper arm movement. , and its action point is selected at the position where the reinforcement rib can be added; The cross-sectional area of ​​the designed reinforcement should meet the following constraints: （3） In the formula, is the shear stress, A is the designed cross-sectional area of ​​the reinforcement; The cross-sectional area of ​​the designed rib is obtained by adjusting according to formula (3), and then the length and width of the rib are selected according to the cross-sectional area. When the torsional force in the actual working condition is greater than that in the limit working condition, the tensile height of the rib is increased as much as possible; Step 6: Perform strength check on the boom with reinforcement ribs by finite element analysis to check whether its stress and displacement are improved. If it still cannot meet the use requirements, return to step 1 to redesign the basic structure of the boom until the strength of the boom meets the use requirements.

2. The method for designing a robot arm reinforcement rib according to claim 1, characterized in that: The adding of the second reinforcing rib in the shear direction of the first reinforcing rib means that the second reinforcing rib is perpendicular to the first reinforcing rib, and the second angle is obtained by adding 90 degrees to the first angle.

3. The method for designing a robot arm reinforcement rib according to claim 1, characterized in that: After adding the second reinforcement, other reinforcements that can locally increase the shear resistance are added alternately with the first reinforcement, taking into account whether the spatial layout is sufficient, the need for actual strength verification, the aesthetics of the layout, or the convenience of processing.

4. The method for designing a robot arm reinforcement rib according to claim 1, characterized in that: The width and height of the reinforcing rib are greater than the wall thickness of the upper arm body.

Images