Pear fruit picking end effector based on bionics and design method

Abstract

The invention relates to a bionics-based pear picking end effector and a design method thereof.The design method includes the steps that firstly, action skills of fruit farmers for picking pears are collected and analyzed, mechanical parameters in the picking process are obtained, and then the structure of the end effector is determined according to physical morphological parameters of the pears in combination with a dionaea muscipula catching structure; the maximum clamping force and the minimum clamping force in the clamping process are calculated by measuring the mechanical property of the pome, and then the tooth pitch and tooth height parameters of the dionaea muscipula bionic clamping teeth are designed, so that it is ensured that the pome is picked together with a fruit stem; according to the opening distance and the rotating angle of the clamped blades, parameters of all connecting rods of the transmission system are determined, and stable and accurate control over the transmission system is achieved; finally, according to the mechanical requirements of the maximum clamping force and the picking action, a proper stepping motor model is selected to drive a clamping and rotating structure, and it is guaranteed that the device is sufficient in power and stable in control; based on the bionics principle, the pear fruit picking device has efficient and stable picking capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural picking equipment, and in particular to a bionics-based pear picking end effector and a design method thereof. Background Art

[0002] With the continuous development of orchard planting industry, the introduction of mechanized picking technology can reduce dependence on manual labor, reduce picking costs, and become an important solution to address labor problems.

[0003] However, at present, pear picking is still mainly done manually. There are relatively few types of end effectors used in mechanized pear picking, and most of them use the method of pulling off or rotating and twisting off. The manipulator pulls the pear downward or outward to forcibly separate the fruit from the stalk, which can easily cause damage to the pear or break the stalk. Although rotating and twisting off is gentler than pulling off, if the twisting force and angle are not accurately controlled, especially when the stalk is thick or the fruit is tightly attached to the fruit branch, it will still cause damage to the fruit or stalk. In the process of fruit picking, fruit farmers usually use experienced techniques, that is, applying shear force at the connection between the stalk and the branch, and lightly picking the fruit together with the stalk to ensure the integrity and quality of the fruit. This picking method can not only reduce damage to the fruit skin and flesh, but also protect the integrity of the stalk and extend the storage time of the fruit.

[0004] In order to meet the actual picking requirements, a bionic pear picking end effector is designed that combines the traditional picking method of fruit farmers to achieve precise picking of fruits and meet the high standards for protecting the fruit stalks during pear picking. This has important practical significance for the development of the pear industry. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a bionics-based pear fruit picking end effector and a design method, which can achieve precise picking of fruits and meet the high standard requirements for protecting the fruit stalks during pear fruit picking, and has important practical significance for the development of the pear fruit industry.

[0006] The present invention is realized by the following technical scheme, providing a bionic pear fruit picking end effector, comprising a bottom plate, an end rotating mechanism driving the bottom plate to swing, and a Venus flytrap bionic clamping mechanism installed at the front end of the bottom plate, wherein the end rotating mechanism comprises a second stepping motor;

[0007] The bionic Venus flytrap clamping mechanism comprises two bionic Venus flytrap clamping blades, the rear end of the bionic Venus flytrap clamping blades is hinged to the bottom plate, the front end of the bionic Venus flytrap clamping blades is provided with a plurality of bionic Venus flytrap clamping teeth, the bionic Venus flytrap clamping teeth of the two bionic Venus flytrap clamping blades are arranged in an interlaced manner, and a pressure sensor is provided on the inner side of the bionic Venus flytrap clamping blades;

[0008] It also includes a transmission system, which includes two mutually meshing connecting rod gears axially connected to the bottom plate, and a first stepper motor for driving any connecting rod gear to rotate. The connecting rod of the connecting rod gear is hinged to one end of the driving rod, and the other end of the driving rod is hinged to the bionic clamping leaf of the Venus flytrap.

[0009] A method for designing the end effector according to claim 1, comprising the following steps:

[0010] S1. Analyze the pear picking skills of fruit farmers and measure the mechanical parameters related to the picking action;

[0011] S2. Combine the pear picking action with the structure of each part of the Venus flytrap to determine the basic structure of the end effector;

[0012] S3. Determine the structure of the Venus flytrap bionic clamping blade according to the measured physical morphological parameters of the pear fruit, including its length, width and arc structure parameters;

[0013] S4. Determine the maximum clamping force during picking according to the measured mechanical property parameters of the pear fruit, and calculate the minimum clamping force required for clamping the pear fruit;

[0014] S5. Determine the pitch, tooth height and number of teeth of the bionic clamping mechanism of the Venus flytrap according to the tooth surface length and the diameter parameters of the pear stalk;

[0015] S6. Determine the structural parameters of each part in the transmission system according to the opening distance and rotation angle of the leaf clamping blades of the Venus flytrap bionic type;

[0016] S7. Determine the model of the first stepper motor in the transmission system according to the maximum clamping force determined in step S4, and determine the model of the second stepper motor in the terminal rotation mechanism according to the mechanical parameters related to the picking action determined in step S1.

[0017] As an optimization, the fruit farmer's pear picking action skills in step S1 include the following steps: first, the fruit farmer approaches the ripe pear fruit, and after confirming the position, the fruit farmer slowly wraps the pear fruit with his palm and ensures that the force does not exceed the tolerance of the fruit. After confirming that it is held, the fingers hold the fruit stalk and twist the fruit along one side, and by applying shear force at the connection between the fruit stalk and the branch, the fruit stalk and the fruit are separated from the branch together, completing the picking of the pear fruit together with the fruit stalk.

[0018] As an optimization, the length L and width W of the Venus flytrap bionic clamping blades depend on the horizontal diameter D and height H of the pear fruit respectively:

[0019] L=k·D

[0020] W=m·H

[0021] Here, k and m are design-dependent scaling factors.

[0022] As an optimization, the arc structure of the Venus flytrap bionic clamping blade depends on the contour curve of the pear fruit: the outer contour of the pear fruit is divided into three parts: the upper contour, the middle contour and the lower contour. By shooting the cross-sectional view of the pear fruit, the contour points of the outer contour of the pear fruit are gradually depicted, and the position coordinates of the contour points of each part are imported into the MATLAB environment, and polynomial curve fitting is performed to obtain the polynomial equation of each part, and the polynomial equation is exported to the three-dimensional drawing software SolidWorks. In SolidWorks, the polynomial equation is used as the driving curve, and the arc structure of the clamping blade is created by the drawing tool. The fitting curve equation is as follows:

[0023] Upper contour: f(x) = -0.003389x 4 +0.133x 3 -1.981x 2 +14.17x-0.8104(R 2 =0.9993)

[0024] Middle contour: f(x) = -0.000004159x 4 +0.0005811x 3 -0.04044x 2 +1.528x+29.84(R 2 =0.9988) Lower contour: f(x) = -0.00254x 4 +0.7135x 3 -75.19x 2 +3522x-0.0006181(R 2 =0.9992).

[0025] As an optimization, compression tests were carried out on pear fruits to measure their relevant mechanical properties and their maximum allowable deformation δ max , combined with the Hertz theory of elastic mechanics to calculate the maximum clamping force that the pear can withstand, first calculate the clamping point x according to the contour curve of the front clamping blade 0 The radius of curvature:

[0026]

[0027] In Hertz's theory, the equivalent radius of curvature R of two surfaces in contact is defined as:

[0028]

[0029] The effective Young's modulus E * Defined as:

[0030]

[0031] According to the relationship between contact radius a and clamping force F:

[0032]

[0033] Where E * Represents the effective elastic modulus, R 1 and R 2 represents the maximum curvature radius of the contact position between the pear and the end effector, E represents the elastic modulus of the pear, μ represents its Poisson's ratio, δ max Indicates the maximum deformation that the pear can withstand.

[0034] At the same time by

[0035] 2F f ≥G

[0036] F f =μF

[0037] G=mg

[0038] get

[0039]

[0040] Thus, the minimum holding force required for picking pears is obtained, where F f is the friction force between the clamping blade and the pear fruit, μ is the friction coefficient between the clamping blade and the pear fruit, and G is the gravity exerted on the pear fruit.

[0041] As an optimization, the pitch, height and number of teeth of the Venus flytrap bionic clamp are related to the length of the clamped blade and the diameter of the pear stalk. Assuming the pitch of the teeth is p and the number of teeth is N:

[0042]

[0043] L=k·D

[0044] have to

[0045]

[0046] Where L is the length of the Venus flytrap bionic clamping blade, p is the distance between teeth, k is a design-related proportional factor, D is the horizontal diameter of the pear,

[0047] The tooth height of the bionic snap-tooth structure of the Venus flytrap is equal to the length x of the pear fruit stalk. When the clamping leaves are closed, the snap-tooth structure is engaged and stuck in the middle and upper part of the fruit stalk. At, the included angle γ between the bionic tooth structure of the Venus flytrap and the tangent line of the end point of the contour on the clamped leaf can be obtained:

[0048]

[0049] As an optimization, the opening distance of the clamping blades is determined by the transverse diameter of the pear fruit, and then the angle of rotation of the clamping blades when opening and closing is obtained:

[0050]

[0051] Wherein, W is the width of the clamping blade, and d is the distance between the two clamping blade tooth structures.

[0052] As an optimization, the first stepper motor in the transmission system is determined according to the maximum clamping force that the pear can withstand and the minimum clamping force required for clamping; the model of the second stepper motor in the terminal rotation mechanism is determined according to the mechanical parameters related to the picking action determined in step S1:

[0053] T static =Fr

[0054] T dynamic =Jα

[0055] T total =T static +T dynamic

[0056] Where T static is the static torque used to keep the load in the desired position, T dynamic is the dynamic torque used to drive the load to move; F is the clamping force required by the load, r is the distance from the rotation axis to the point of force application; J is the total inertia of the system, α is the angular acceleration, T total It is the sum of static torque and dynamic torque.

[0057] The beneficial effects of the present invention are as follows: the bionic-based pear fruit picking end effector and design method of the present invention realizes a design with both precision and bionic characteristics by drawing on the manual picking skills of fruit farmers and the capture mechanism of the Venus flytrap. The size and shape of the clamping blades are determined by measuring the physical morphological parameters of the pear fruit and combining the data fitting method so that they can fit closely to the contour of the pear fruit, thereby ensuring uniform and stable support for the fruit during the clamping process and reducing damage to the fruit. The two teeth of the clamping blades can fix and protect the integrity of the fruit stalk, firmly clamp the fruit stalk, enhance the clamping stability, ensure that the fruit is picked intact with the fruit stalk, and improve the preservation and storage performance of the fruit.

[0058] This design method combines precise parameter measurement with the principle of bionics to make the end effector more in line with actual needs in terms of mechanical properties and structural design. This design concept not only reduces fruit damage during picking, but also improves picking efficiency and stability, ultimately achieving accurate and efficient pear picking. The present invention not only meets the needs of modern orchards for high-quality and efficient picking, but also promotes the innovative development of fruit picking mechanization. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a schematic diagram of the overall structure of the end effector of the present invention;

[0060] Figure 2 It is a schematic diagram of the bionic clamping mechanism of the Venus flytrap of the present invention;

[0061] Figure 3 It is a schematic diagram of the transmission system structure of the present invention;

[0062] Figure 4 It is a schematic diagram of the terminal rotation mechanism of the present invention;

[0063] Figure 5 It is a schematic diagram of the working of the present invention;

[0064] Figure 6 It is a flow chart of the design method of the present invention;

[0065] Figure 7 It is a schematic diagram of the method and principle of picking pears of the present invention;

[0066] Figure 8 It is a schematic diagram of the structure of the Venus flytrap of the present invention;

[0067] As shown in the figure:

[0068] 3-1, insect trap, 3-2, stinging hair, 3-3, tactile hair, 4-1, bottom plate, 4-2, transmission system, 4-3, first stepper motor, 4-4, Venus flytrap bionic clamping mechanism, 4-5, pressure sensor, 4-6, end rotation mechanism, 4-7, Venus flytrap bionic clamping teeth, 6-1, connecting rod gear, 6-2, driving rod, 6-3, fixing rod, 6-4, connecting rod, 6-5, hinge pin, 6-6, fixing rod bolt, 7-1, bottom plate fixing bolt, 7-2, second stepper motor. DETAILED DESCRIPTION

[0069] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0070] like Figures 1 to 8 As shown, a bionics-based pear fruit picking end effector of the present invention includes a base plate 4-1, an end rotating mechanism 4-6 for driving the base plate 4-1 to swing, and a Venus flytrap bionic clamping mechanism 4-4 installed at the front end of the base plate 4-1, the end rotating mechanism 4-6 includes a second stepper motor 7-2 and a swing frame fixedly connected to the rotating shaft of the second stepper motor 7-2, and the rear end of the base plate 4-1 is fixedly connected to the front end of the swing frame by the base plate fixing bolts 7-1, thereby realizing the swing of the base plate 4-1.

[0071] The bionic clamping mechanism 4-4 of the Venus flytrap includes two bionic clamping blades of the Venus flytrap, which are arc-shaped. The shape formed by the two bionic clamping blades of the Venus flytrap is adapted to the pear fruit. The rear end of the bionic clamping blade of the Venus flytrap is hinged to the bottom plate 4-1. Specifically, the front end of the bottom plate 4-1 is fixed with two fixing rods 6-3 through fixing rod bolts 6-6. A connecting rod 6-4 is fixed to the outer side of the bionic clamping blade of the Venus flytrap, and the rear end of the connecting rod 6-4 is hinged to the fixing rod 6-3.

[0072] The front end of the Venus flytrap bionic clamping blade is provided with a plurality of Venus flytrap bionic clamping teeth 4-7, and the Venus flytrap bionic clamping teeth of the two Venus flytrap bionic clamping blades are arranged in a staggered manner.

[0073] Pressure sensors 4-5 are provided on the inner side of the Venus flytrap bionic clamping blades for detecting the clamping force.

[0074] like Figure 3 As shown, it also includes a transmission system 4-2, which includes two mutually meshing connecting rod gears 6-1 axially connected to the base plate 4-1, the connecting rod gear 6-1 has a connecting rod fixed on the gear, and the two connecting rod gears 6-1 are symmetrically arranged, and also includes a first stepper motor 4-3 for driving any connecting rod gear 6-1 to rotate, thereby realizing the synchronous rotation of the two connecting rod gears 6-1.

[0075] The connecting rod of the connecting rod gear 6-1 is hinged to one end of the driving rod 6-2, and the other end of the driving rod 6-2 is hinged to the bionic clamping blade of the Venus flytrap.

[0076] A method for designing an end effector comprises the following steps:

[0077] S1. Collect relevant information and conduct field investigations to analyze the pear picking skills of fruit farmers and measure the mechanical parameters related to the picking action;

[0078] S2. Combine the pear picking action with the structure of each part of the Venus flytrap to determine the basic structure of the end effector;

[0079] S3. Determine the structure of the Venus flytrap bionic clamping blade according to the measured physical morphological parameters of the pear fruit, including its length, width and arc structure parameters;

[0080] S4. Determine the maximum clamping force during picking according to the measured mechanical property parameters of the pear fruit, and calculate the minimum clamping force required for clamping the pear fruit;

[0081] S5. Determine the pitch, tooth height and number of teeth of the bionic clamping mechanism of the Venus flytrap according to the tooth surface length and the diameter parameters of the pear stalk;

[0082] S6. Determine the structural parameters of each part in the transmission system according to the opening distance and rotation angle of the leaf clamping blades of the Venus flytrap bionic type;

[0083] S7. Determine the model of the first stepper motor in the transmission system according to the maximum clamping force determined in step S4, and determine the model of the second stepper motor in the terminal rotation mechanism according to the mechanical parameters related to the picking action determined in step S1.

[0084] The pear picking action technique of the fruit farmer in step S1 includes the following steps: first, the fruit farmer approaches the ripe pear fruit, and after confirming the position, the fruit farmer slowly wraps the pear fruit with his palm and ensures that the force does not exceed the tolerance of the fruit, and after confirming that the grip is firm, the fingers hold the fruit stalk and twist the fruit along one side, and the fruit stalk is separated from the branch together with the fruit by applying shear force at the connection between the fruit stalk and the branch, thereby completing the efficient picking of the pear fruit and the fruit stalk, and ensuring the integrity and quality of the fruit.

[0085] The principle of picking pears by fruit farmers is the same. The same picking method is used to measure the squeezing force F on the pears during picking through the pressure sensor. N , Shear force F at the connection between the fruit stalk and the branch τ and the angle at which the fruit stalk is tilted to the horizontal plane Provide a reference for subsequent design methods.

[0086] like Figure 8 As shown, the structure of the Venus flytrap mainly includes the insect trap 3-1 and the bristles 3-2 on its edge, the internal tactile hairs 3-3 and other structures. Combined with the picking action, the basic structure of the designed end effector is as follows Figure 1 , including a Venus flytrap bionic clamping blade 4-4 and a Venus flytrap bionic clamping tooth structure 4-7 on its edge, a Venus flytrap bionic pressure sensor 4-5 inside thereof, and the like.

[0087] The length L and width W of the Venus flytrap bionic clamping blades depend on the horizontal diameter D and height H of the pear fruit respectively:

[0088] L=k·D

[0089] W=m·H

[0090] Among them, k and m are proportional factors related to the design. In this embodiment, k is selected to be 1.2-1.6 and m is selected to be 1.1-1.5 to ensure the coverage and clamping effect of the clamping blades.

[0091] The arc structure of the Venus flytrap bionic clamping blade depends on the contour curve of the pear fruit: the outer contour of the pear fruit is divided into three parts: an upper contour, a middle contour and a lower contour. This helps to more accurately depict the shape of the pear fruit to ensure that the clamping blade can adapt to the contours of different parts. By taking a cross-sectional view of the pear fruit, the image is ensured to be clear and accurately reflect the appearance characteristics of the pear fruit. The cross-sectional view is imported into the Get Data Graph Digitizer software. Through the function of the software, the contour points of the outer contour of the pear fruit are gradually depicted, which are divided into three parts: an upper contour, a middle contour and a lower contour. The coordinates (x, y) of each point will be accurately recorded for subsequent analysis. The position coordinates of the contour points of each part are imported into the MATLAB environment. In MATLAB, open the Curve Fitting Toolbox, select the polynomial curve fitting function, perform polynomial curve fitting according to the contour points of different parts, and obtain the polynomial equation of each part. These equations will be used to generate the arc structure of the clamping blade. After completing the fitting, carefully check the goodness of fit (such as R square value) of the obtained polynomial equation to ensure that it can accurately represent the contour of the pear fruit. If necessary, adjust the parameters to obtain a better fitting effect. Export the polynomial equation to the 3D drawing software SolidWorks. In SolidWorks, use the polynomial equation as the driving curve and use the drawing tool to create the arc structure of the clamping blade. The fitting curve equation is as follows:

[0092] Upper contour: f(x) = -0.003389x 4 +0.133x 3 -1.981x 2 +14.17x-0.8104(R 2 =0.9993)

[0093] Middle contour: f(x) = -0.000004159x 4 +0.0005811x 3 -0.04044x 2 +1.528x+29.84(R 2 =0.9988)

[0094] Lower contour: f(x) = -0.00254x 4 +0.7135x 3 -75.19x 2 +3522x-0.0006181(R 2 =0.9992).

[0095] The compression test of pears was carried out on the workbench of Shimadzu's small desktop EZ-TEST testing machine (EZ-SX), and its related mechanical performance parameters and its maximum allowable deformation δmax were measured. The maximum clamping force that the pears can withstand was calculated by combining the Hertz theory of elastic mechanics.

[0096] First, the clamping point x is calculated based on the contour curve of the front clamping blade. 0 The radius of curvature:

[0097]

[0098] In Hertz's theory, the equivalent radius of curvature R of two surfaces in contact is defined as:

[0099]

[0100] The effective Young's modulus E * Defined as:

[0101]

[0102] According to the relationship between contact radius a and clamping force F:

[0103]

[0104] Here, the material of the clamping blade is much harder than the pear fruit, so only the deformation of the pear fruit is considered, and the deformation of the clamping blade is ignored. * Represents the effective elastic modulus, R 1 and R 2 represents the maximum curvature radius of the contact position between the pear and the end effector, E represents the elastic modulus of the pear, μ represents its Poisson's ratio, δ max Indicates the maximum deformation that the pear can withstand.

[0105] At the same time by

[0106] 2F f ≥G

[0107] F f =μF

[0108] G=mg

[0109] get

[0110]

[0111] Thus, the minimum holding force required for picking pears is obtained, where F f is the friction force between the clamping blade and the pear fruit, μ is the friction coefficient between the clamping blade and the pear fruit, and G is the gravity exerted on the pear fruit.

[0112] The pitch, height and number of teeth of the bionic clamping teeth of the Venus flytrap are related to the length of the clamped blade and the diameter of the pear stalk. Assuming the pitch of the teeth is p and the number of teeth is N:

[0113]

[0114] L=k·D

[0115] have to

[0116]

[0117] Where L is the length of the Venus flytrap bionic clamping blade, p is the distance between teeth, k is a design-related proportional factor, D is the horizontal diameter of the pear,

[0118] The tooth height of the bionic snap-tooth structure of the Venus flytrap is equal to the length x of the pear fruit stalk. When the clamping leaves are closed, the snap-tooth structure is engaged and stuck in the middle and upper part of the fruit stalk. At, the included angle γ between the bionic tooth structure of the Venus flytrap and the tangent line of the end point of the contour on the clamped leaf can be obtained:

[0119]

[0120] As an optimization, the opening distance of the clamping blades is determined by the transverse diameter of the pear fruit, and then the angle of rotation of the clamping blades when opening and closing is obtained:

[0121]

[0122] Wherein, W is the width of the clamping blade, and d is the distance between the two clamping blade tooth structures.

[0123] As an optimization, the first stepper motor in the transmission system is determined according to the maximum clamping force that the pear can withstand and the minimum clamping force required for clamping; the model of the second stepper motor in the terminal rotation mechanism is determined according to the mechanical parameters related to the picking action determined in step S1:

[0124] T static =Fr

[0125] T dynamic =Jα

[0126] T total =T static +T dynamic

[0127] Where T static is the static torque used to keep the load in the desired position, T dynamic is the dynamic torque used to drive the load to move; F is the clamping force required by the load, r is the distance from the rotation axis to the point of force application; J is the total inertia of the system, α is the angular acceleration, T totalIt is the sum of static torque and dynamic torque.

[0128] Finally, the model structure diagram is drawn in Solidworks, and the key components of the drawn prototype model are simulated and analyzed to determine the optimal combination of dimensional parameters such as the size and curvature of the clamping blade opening, the rod size of the transmission system, etc., to optimize and improve the structure of key components, and to optimize the overall solution.

[0129] Of course, the above description is not limited to the above examples. Technical features not described in the present invention can be achieved by or by using existing technologies, which will not be described here. The above embodiments and drawings are only used to illustrate the technical scheme of the present invention and are not limitations of the present invention. The present invention is described in detail with reference to the preferred implementation methods. Ordinary technicians in this field should understand that changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention do not depart from the purpose of the present invention, and should also fall within the scope of protection of the claims of the present invention.

Claims

1. A bionic pear picking end effector, characterized by: It comprises a base plate (4-1), an end rotating mechanism (4-6) for driving the base plate (4-1) to swing, and a Venus flytrap bionic clamping mechanism (4-4) installed at the front end of the base plate (4-1), wherein the end rotating mechanism (4-6) comprises a second stepping motor (7-2); The flytrap bionic clamping mechanism (4-4) comprises two flytrap bionic clamping blades, the rear ends of the flytrap bionic clamping blades are hinged to the bottom plate (4-1), the front ends of the flytrap bionic clamping blades are provided with a plurality of flytrap bionic clamping teeth, the flytrap bionic clamping teeth of the two flytrap bionic clamping blades are arranged in an alternating manner, and the inner sides of the flytrap bionic clamping blades are provided with pressure sensors (4-5); The invention also comprises a transmission system, wherein the transmission system comprises two mutually meshing connecting rod gears (6-1) axially connected to the bottom plate (4-1), and a first stepper motor (4-3) driving any connecting rod gear (6-1) to rotate, wherein the connecting rod of the connecting rod gear (6-1) is hinged to one end of the driving rod (6-2), and the other end of the driving rod (6-2) is hinged to the bionic clamping blade of the Venus flytrap.

2. A method for designing the end effector according to claim 1, characterized in that: The steps include: S1. Analyze the pear picking skills of fruit farmers and measure the mechanical parameters related to the picking action; S2. Combine the pear picking action with the structure of each part of the Venus flytrap to determine the basic structure of the end effector; S3. Determine the structure of the Venus flytrap bionic clamping blade according to the measured physical morphological parameters of the pear fruit, including its length, width and arc structure parameters; S4. Determine the maximum clamping force during picking according to the measured mechanical property parameters of the pear fruit, and calculate the minimum clamping force required for clamping the pear fruit; S5. Determine the pitch, tooth height and number of teeth of the bionic clamping mechanism of the Venus flytrap according to the tooth surface length and the diameter parameters of the pear stalk; S6. Determine the structural parameters of each part in the transmission system according to the opening distance and rotation angle of the leaf clamping blades of the Venus flytrap bionic type; S7. Determine the model of the first stepper motor in the transmission system according to the maximum clamping force determined in step S4, and determine the model of the second stepper motor in the terminal rotation mechanism according to the mechanical parameters related to the picking action determined in step S1.

3. The design method according to claim 2, characterized in that: The pear picking action technique of the fruit farmer in step S1 includes the following steps: first, the fruit farmer approaches the ripe pear fruit, and after confirming the position, the fruit farmer slowly wraps the pear fruit with his palm and ensures that the force does not exceed the tolerance of the fruit. After confirming that the grip is firm, the fingers hold the fruit stalk and twist the fruit along one side, and by applying shear force at the connection between the fruit stalk and the branch, the fruit stalk and the fruit are separated from the branch together, thereby completing the picking of the pear fruit together with the fruit stalk.

4. The design method according to claim 2, characterized in that: The length L and width W of the Venus flytrap bionic clamping blades depend on the horizontal diameter D and height H of the pear fruit respectively: L=k·D W=m·H Here, k and m are design-dependent scaling factors.

5. The design method according to claim 2, characterized in that: The arc structure of the Venus flytrap bionic clamping blade depends on the contour curve of the pear fruit: the outer contour of the pear fruit is divided into three parts: the upper contour, the middle contour and the lower contour. The contour points of the outer contour of the pear fruit are gradually depicted by photographing the cross-sectional view of the pear fruit. The position coordinates of the contour points of each part are imported into the MATLAB environment, and polynomial curve fitting is performed to obtain the polynomial equation of each part. The polynomial equation is exported to the three-dimensional drawing software SolidWorks. In SolidWorks, the polynomial equation is used as a driving curve, and the arc structure of the clamping blade is created by a drawing tool. The fitting curve equation is as follows: Upper contour: f(x) = -0.003389x 4 +0.133x 3 -1.981x 2 +14.17x-0.8104(R 2 =0.9993) Middle contour: f(x) = -0.000004159x 4 +0.0005811x 3 -0.04044x 2 +1.528x+29.84(R 2 =0.9988) Lower contour: f(x) = -0.00254x 4 +0.7135x 3 -75.19x 2 +3522x-0.0006181(R 2 =0.9992).

6. The design method according to claim 2, characterized in that: The compression test was carried out on the pear fruit to measure its relevant mechanical performance parameters and its maximum allowable deformation δmax. The maximum clamping force that the pear fruit can withstand was calculated by combining the Hertz theory of elastic mechanics. First, the radius of curvature of the clamping point x0 is calculated based on the contour curve of the clamping blade: In Hertz's theory, the equivalent radius of curvature R of two surfaces in contact is defined as: The effective Young's modulus E * Defined as: According to the relationship between contact radius a and clamping force F: Where E * represents the effective elastic modulus, R1 and R2 represent the maximum curvature radius of the contact position between the pear and the end effector, E represents the elastic modulus of the pear, μ represents its Poisson's ratio, δ max Indicates the maximum deformation that the pear can withstand. At the same time by <h2 style=";text-align:left;direction:ltr">2F<h2 style=";text-align:left;direction:ltr"> f <h2 style=";text-align:left;direction:ltr"> ≥G F f =μF G=mg get Thus, the minimum holding force required for picking pears is obtained, where F f is the friction force between the clamping blade and the pear fruit, μ is the friction coefficient between the clamping blade and the pear fruit, and G is the gravity exerted on the pear fruit.

7. The design method according to claim 2, characterized in that: The pitch, height and number of teeth of the bionic clamping teeth of the Venus flytrap are related to the length of the clamped blade and the diameter of the pear stalk. Assuming the pitch of the teeth is p and the number of teeth is N: L=k·D have to Among them, L is the length of the Venus flytrap bionic clamping blade, p is the distance between teeth, k is a design-related proportional factor, D is the horizontal diameter of the pear, The tooth height of the bionic snap-tooth structure of the Venus flytrap is equal to the length x of the pear fruit stalk. When the clamping leaves are closed, the snap-tooth structure is engaged and stuck in the middle and upper part of the fruit stalk. At, the included angle γ between the bionic tooth structure of the Venus flytrap and the tangent line of the end point of the contour on the clamped leaf can be obtained:

8. The design method according to claim 2, characterized in that: The opening distance of the clamping blades is determined by the transverse diameter of the pear, and the angle of rotation of the clamping blades when opening and closing is obtained: Wherein, W is the width of the clamping blade, and d is the distance between the two clamping blade tooth structures.

9. The design method according to claim 2, characterized in that: According to the maximum clamping force that the pear can withstand and the minimum clamping force required for clamping, the first stepper motor in the transmission system is determined; according to the mechanical parameters related to the picking action determined in step S1, the model of the second stepper motor in the terminal rotation mechanism is determined: T static =Fr T dynamic =Jα T total =T static +T dynamic Where T static is the static torque used to keep the load in the desired position, T dynamic is the dynamic torque used to drive the load to move; F is the clamping force required by the load, r is the distance from the rotation axis to the point of force application; J is the total inertia of the system, α is the angular acceleration, T total It is the sum of static torque and dynamic torque.

Images