Design method of picking part of end effector for picking ginkgo flower spikes
阅读说明：本技术 用于采摘银杏花穗的末端执行器的采摘部分的设计方法 (Design method of picking part of end effector for picking ginkgo flower spikes ) 是由 汪希伟 刘佳傲 赵茂程 曾帆 于 2021-07-21 设计创作，主要内容包括：一种用于采摘银杏花穗的末端执行器的采摘部分的设计方法,步骤包括：1)通过银杏花穗的采样,确定设计方案；2)根据设计方案进行结构设计；3)对设计得到结构进行仿真分析。步骤2)中,咬合功能结构：通过模仿博比特虫口腔设计咬合机构,能够准确咬合包裹住花穗；分离功能结构：通过模仿博比特虫抓住猎物后用勾爪由外向内翻转将猎物吞进体内,设计末端执行器口腔咬合包裹花穗后的分离花穗机构,将花穗从短枝上分离,实现分离的功能；吞咽功能结构：通过模仿博比特虫将猎物通过喉部咽进身体,其喉部呈空管状,设计孔洞结构将分离后的花穗,从口腔内部的管道进入收集箱。本方法确保末端执行器的采摘部分在采摘花穗过程中不伤害到短枝和花穗。(A method of designing a picking section of an end effector for picking a ginkgo flower spike, the steps comprising: 1) determining a design scheme through sampling of the ginkgo spica; 2) carrying out structural design according to a design scheme; 3) and carrying out simulation analysis on the designed structure. In step 2), the occlusion function structure: by designing the occlusion mechanism by simulating the oral cavity of the Bobitis insect, the flower spike can be accurately occluded and wrapped; separation function structure: the method comprises the following steps of (1) swallowing a prey into a human body by overturning the prey from outside to inside by using a hook claw after the prey is grabbed by a simulated Bober worm, designing a spica separating mechanism of which the oral cavity of an end effector is occluded and wraps the spica, and separating the spica from short branches to realize the separating function; the swallowing function structure: through imitating the bobi worm, prey enters the body through the throat, the throat is in a hollow tube shape, and the spica after separation enters the collecting box from the pipeline inside the oral cavity by designing the hole structure. The method ensures that the picking part of the end effector does not damage short branches and spica in the picking process of the spica.)
1. A method of designing a picking section of an end effector for picking a ginkgo flower spike, the steps comprising: 1) determining a design scheme through sampling of the ginkgo spica; 2) carrying out structural design according to a design scheme; 3) carrying out simulation analysis on the designed structure, and is characterized in that in the step 2), three functional structures of occluding the spica, separating the spica and swallowing the spica of the picking part are respectively designed by simulating the head structure of the Bobitis insect;
2.1) occlusion function structure: by designing the occlusion mechanism by simulating the oral cavity of the Bobitis insect, the flower spike can be accurately occluded and wrapped;
2.2) separation function structure: the method comprises the following steps of (1) swallowing a prey into a human body by overturning the prey from outside to inside by using a hook claw after the prey is grabbed by a simulated Bober worm, designing a spica separating mechanism of which the oral cavity of an end effector is occluded and wraps the spica, and separating the spica from short branches to realize the separating function;
2.3) swallowing function structure: the prey is swallowed into the body through the throat of the bober by simulating the bober, the throat of the bober is in a hollow tube shape, and the separated spica enters the collecting box from a pipeline in the oral cavity by designing a hole structure;
wherein:
2.1) the occlusion mechanism is designed as a rotary structure: the force for picking up the flower spikes and the force for picking up the leaves are known to be very small through the results of the mechanical property measurement of the flower spikes and the leaves; the switch closing angle of the rotary structure is adjustable, and the occlusion range is large; in the occlusion function structure design, a protective cover for occlusion fixation is designed to ensure that the flower spikes cannot fall off from the oral cavity when the flower spikes are picked in the oral cavity of the end effector;
2.2) the design of the flower spike separating mechanism is a combing structure: because the size and the weight of the ginkgo flower are very small, the flower spikes are separated on the occlusion mechanism by adopting a combing and brushing principle;
the drive of the rotary structure and the drive of the combing structure in 2.1) and 2.2) adopt an air pressure drive device to drive the actuator to move; the pneumatic driving device does not generate electric sparks, and stepless speed change is realized through air pressure regulation.
2. The method of claim 1, wherein the step 1) comprises:
1.1) geometric characteristics of Ginkgo spica
Collecting branches of mature ginkgo spica, taking the spica of a short branch as a group of data, wherein the number of the spica and the number of leaves of each short branch are different;
collecting branches of different ginkgo trees, and measuring 100 groups of data;
the length and the maximum diameter of the flower spike are measured, the length of the ginkgo flower spike is 24-27 mm, the maximum diameter is 5-7 mm, and data support is provided for the design of a bite functional structure;
the number of the spica on each short branch is 4-6, a plurality of blades are arranged, the spica and the blades on the whole short branch are all swallowed each time by determining an occlusion functional structure, and picking of the spica and the blades is distinguished through the force required by picking;
1.2) spacing of the short branches of Ginkgo biloba
The short branch distance with the included angle of the adjacent planes less than 45 degrees is 80mm-100mm, when the picking part starts picking the flower spike on one short branch, the occlusion mechanism of the picking part can not interfere with the adjacent flower spike in the process from opening to closing, so the radius of the maximum opening range of the end effector is designed to be less than 100 mm; in order to ensure that all the leaves of the flower spike on the short branch can be swallowed, the radius of the minimum opening range of the actuator must be more than 30 mm; the mouth opening radius of the final design actuator is 30mm-100 mm;
1.3) mechanical Properties of Ginkgo spica and leaves
After the ginkgo spica is swallowed by the occlusion mechanism, the spica is picked by the separation function structure, and the force for picking the spica needs to be measured;
during the experiment, 3-5 spiders are arranged on each short branch of the cut ginkgo branches, 4-6 ginkgo leaves are arranged on each short branch, and the ginkgo spiders are picked to reduce the interference of picked leaves and reduce the damage to the leaves as much as possible, so the force for picking the ginkgo leaves is measured;
the flower spikes and the leaves grow on the short branches, the actuator inevitably contacts the short branches when picking the flower spikes, and the force required for breaking the short branches is measured in order to prevent the actuator from pinching the short branches when closing;
the 3 forces are tensile tests by adopting a horizontal pull type, and the picking forces of 100 groups of ginkgo flower spikes and leaves are measured by using a dynamometer in the tests; the force for picking up the ginkgo spica is 0.8N-1.3N, the force for picking up the leaves is 3N-4.3N, and the force required for breaking the short branches exceeds 20N; because the leaves are not damaged as much as possible when the flower spikes are picked, and the end effector cannot clamp the short branches, the minimum force for picking the leaves is about 3N, the force for picking the flower spikes is required to be less than 3N, and the minimum force for picking the flower spikes is about 1N; when the actuator clamps the short branch, the force applied to the short branch must be less than 20N.
3. The method for designing a picking part of an end effector for picking ginkgo spices according to claim 1, wherein in the step 3), a three-dimensional model of the picking part of the end effector is established through SolidWorks, a SW2.URDF plug-in is installed, a coordinate system and a reference shaft are inserted into the three-dimensional model, and finally the established URDF file is guided into an ROS Moveit simulation environment for carrying out simulation picking of the ginkgo spices by the picking part of the end effector, and the simulation results are sorted and analyzed.
4. The method of claim 1, wherein the picking section of the end effector is designed to pick the head of ginkgo biloba
2.1) occlusion function structure: is designed as a plurality of identical jaws, which are symmetrical about a straight line 1; the bottom of the clamping jaw is rotatably connected to the clamping jaw base, and the rotating axis is vertical to the straight line 1; the clamping jaw is driven to rotate by a first driving mechanism; the clamping jaw comprises an occlusion cover and a separation mechanism; the top end of the occlusion cover 1 is provided with a notch; the state formed by the rotation of each clamping jaw is divided into a closed state and an open state; under a closed state, the side edges of the occlusion covers of the adjacent clamping jaws are attached, each occlusion cover encloses a hollow cavity, and the gap of each occlusion cover encloses a through hole;
2.2) separation function structure: the separation function structure is realized by the separation mechanism; the separating mechanism is arranged on the inner side of the occlusion cover; the separating mechanism is a brush roller which is driven to rotate by a second driving mechanism;
2.3) swallowing function structure: the clamping jaw base is cylindrical, the front end opening of the clamping jaw base is communicated with the hollow cavity, and the rear end opening of the clamping jaw base is connected with a pipeline; the axis of the clamping jaw base coincides with the straight line l; under the closed state, the bottom edge of the occlusion cover of each clamping jaw is attached to the top edge of the side wall of the clamping jaw base; a funnel is connected between the rear end opening of the clamping jaw base and the pipeline; the big mouth one end of funnel is connected with the rear end opening of clamping jaw base, and the osculum one end of funnel is connected the pipeline.
5. The design method of a picking section of an end effector for picking maidenhair ears as claimed in claim 4, characterized in that the number of the gripping jaws is 3; the bite cover is part of a spherical cap-like shape.
6. The method of claim 4, wherein the first drive mechanism is a pneumatic cylinder; the cylinder block of cylinder rotates to be connected in the outer wall of clamping jaw base, and the piston rod of cylinder rotates to be connected in the outer wall of interlock cover.
7. The method of claim 4, wherein the brush roller is formed by a plastic rod externally connected with nylon wires, the nylon wires are radial around the axis of the plastic rod; the second driving mechanism is a pneumatic motor, a rotor of the pneumatic motor is connected with the plastic rod, and the pneumatic motor is connected with the inner wall of the occlusion cover; the axis of the plastic rod is coplanar with line 1.
8. The method of designing a picking section of an end effector for picking a ginkgo biloba head as claimed in claim 7, wherein the mechanical analysis is further performed:
1) mechanical property of the brush roller and type selection of the pneumatic motor:
the table 1 is a parameter table of the pneumatic motor.
TABLE 1 pneumatic motor parameter table
The minimum force required by picking ginkgo leaves is about 3N, the length L of the rolling brush is 5cm, the shaft diameter D is 1cm, and the radius R of the whole rolling brush is 2 cm. Because the bristles are soft and have certain deformability, the bristles can be damaged along with the working time, and the minimum force for brushing the blades by the rolling brush is set to be F0＝3N；
T＝F×r (1)
The shaft radius r of the pneumatic motor is 5mm, and the axial radius r is obtained by substituting the radius into the formula 1),
t is 0.015 N.m, the rated torque of the pneumatic motor is 0.012 N.m, meet the requirements;
2) analyzing short branch dynamics by using an occlusion cover and selecting a cylinder type:
in order to reduce the overall mass of the end effector, a small air cylinder is selected, the diameter of the air cylinder is 16mm, and the air cylinder can provide 0.16 N.m under the pressure of 0.5MPa as shown in the parameters in Table 2;
TABLE 2 Cylinder parameter Table
CD is arranged as an occlusion cover for clamping short branches, AB is an air cylinder and a piston rod, A, C is fixed on a base of the occlusion cover, and the air cylinder pushes the occlusion cover to be closed and simultaneously inflatesA cylinder AB; so that the cylinder drives to provide a force F0Output torque M to the engaging cover DE;
distance of AC is l1Approximately 8.6cm, the length of AB is l2About 4.5cm, and AB length of l1Approximately equal to 8.2cm, the length of BC is l2About 7.5cm, BD length of l3Approximately equal to 3cm, and the included angle between the cylinder AB and the occlusion cover is theta0；
When the occlusion cover contacts the short branch, the point D of the occlusion cover receives the reaction force F of the short branch;
suppose the end effector part is made of hard aluminum and the mass of the cylinder AB is m1Approximately equals 1.2kg, and the mass of the occlusion cover CD is m2≈0.3kg
Because the occlusion cover CD is powered by the cylinder AB, the virtual displacement delta theta is generated at the moment when the occlusion cover contacts the short branch, and the virtual displacement at the point B is
δSB＝l2δθ (3-2)
The engaging cover CD is subjected to the gravity of m2g, the virtual displacement in the action direction is
Then cylinder AB gravity m1The virtual displacement under the action of g is
The virtual displacement of the applied force at point D is
From the principles of imaginary work, equations can be derived
Mδθ+m1gδO1+m2gδO2＝FδSD (3-6)
δ S is equally divided on both sides of formula (3-8)DCan obtain the product
By bringing the compounds of the formulae (3-2), (3-3), (3-4) and (3-5) into (3-7), a compound of the formula
Will l2≈7.5cm，l3＝3cm，θ028 degree embedded type (3-8)
Output torque M ═ F0l0 (3-9)
The cylinder providing a pressure of F0＝PS＝500000×0.004×0.004×3.14＝25.12N
F is to be0＝25.12N，l0About.0.5 cm into (3-9)
M＝F0l0＝0.1256N·m
M is to be1，m2The value of M is brought to F ≈ 15.2N in formula (3-8),
the force required by the short branch breaking is 20N, F is approximately equal to 15.2N and is less than 20N, so that the cylinder is selected, the force is lower than 20N when the occlusion cover clamps the short branch, the short branch cannot be clamped, and the design requirement is met.
Technical Field
The invention belongs to the technical field of forestry machinery, and particularly relates to a design method of a picking part of an end effector for picking ginkgo flower spikes.
Background
A mechanical system of a common fruit and vegetable picking robot consists of a walking mechanism, a mechanical arm and an end effector.
Picking ginkgo spica, wherein ginkgo is a tree and is a rare tree species, and the ginkgo needs decades of time from planting to flowering and fruiting, so that short-branch leaves are not damaged as much as possible during picking; the gingko spica is small in size and weak in body, so that the end effector has high control requirements, and the traditional picking robot cannot meet the requirements for picking the gingko spica. For the grafted male plant gingko in a plantation, the gingko is different from the planted vegetables, and most of the vegetables are annual, so that before fruits are harvested, stems and leaves of the crops can be removed, and the interference on picking can be reduced. However, the ginkgo biloba has a long growth cycle, so that leaves and short branches are not damaged as much as possible when picking up spica.
The core technology of the picking robot is the design of an end effector which directly acts on a picking target, fruits picked in the agriculture and forestry production process are generally fragile, and the shapes and the growth conditions of the same fruits are different, so that the structure and the mechanical property of the end effector are accurate. Meanwhile, in the picking process, the fruits and the branches and leaves of the crops are easily damaged, for example, the position of the fruits is judged wrongly or the positioning is not accurate enough; the clamping force of the end effector gripping mechanism on the target exceeds the maximum bearing force of the target; the end effector is unstable in grabbing, and fruits can easily fall off, so that picking waste is caused, and the picking efficiency is reduced. For the grasping action, if the traditional end effector is used for grasping, fruits are often crushed due to overlarge grasping force or clamping force, so the design of the end effector structure and the control of the end effector are very important.
Disclosure of Invention
The ginkgo flower spikes and the ginkgo leaves are grown on the short branches of the ginkgo branches, and the shapes, the volumes and the colors of the ginkgo flower spikes are similar.
Through observation of field gingkoes and mechanical test of leaves of the flower ears, and data arrangement and analysis, the force required for picking the flower ears of the gingkoes is about one third of that of the leaves, and in order to avoid injuring the leaves and short branches, the flower ears are picked by a roller brush.
The invention researches the mechanical oral part of the end effector of the ginkgo spica intelligent picking system, specifically realizes the scheme and mechanical structure design of the action of separating the target spica from the branch of the picking mechanism, and carries out picking verification in a virtual simulation environment.
The picking end effector takes ginkgo spica as a picking object, and the end effector simulates the hunting of the bobtitus, wherein:
the mouth device of the bionic bocha worm is a claw holding mechanism which is connected at the tail end of a mechanical arm and used for coarsely positioning the mechanical arm and the picked flowering branches.
The mouth of the bionic boccaro is a picking part, and the picking mechanism is connected to the tail end of the mechanical arm and used for wrapping the picked flower spike and separating the flower spike from the flower branch and finally sending the flower spike into the conveying pipeline to the collecting box.
The bionic bocicla beetle body is a rotary mechanism which is connected between the mechanical arm and the picking mechanism and is used for adjusting the position between the picking mechanism and the flower spike.
The invention mainly relates to a picking part of an end effector, which is used for simulating the oral cavity part of a Bobitis insect and is responsible for picking spica and swallowing the spica.
Firstly, analyzing the design requirements of the integral end effector, and integrating the different design requirements of three bionic parts of an oral cavity, a worm body and a mouth device; and then carrying out an on-site experiment, and collecting the size and mechanical data of the ginkgo spica, the ginkgo leaves and the ginkgo braches.
Through the observation and research of the oral action of the mackbrood eating prey and the research of the existing picking robot end effector, a design scheme of a mechanical picking part (namely a bionic oral part) of the end effector is provided, then the specific design of a transmission mechanism and a picking mechanism is carried out, and whether the structure meets the design requirement of the mechanical oral structure is analyzed, and the structure is improved as required. Then, a three-dimensional model of the oral cavity of the end effector is established through SolidWorks, a SW2.URDF plug-in is installed, a coordinate system and a reference axis are inserted into the three-dimensional model, finally, the established URDF file is guided into an ROS Moveit simulation environment, the picking part (namely the bionic oral cavity part) of the end effector is simulated to pick ginkgo spica, and simulation results are sorted and analyzed.
For consistency of description terms, the term "oral cavity" is used hereinafter to mean the "plucked portion".
The design method comprises the following steps:
1. mechanical and geometric data acquisition
The physical characteristics of the ginkgo spica and the ginkgo leaf are the basis for designing an end effector mechanism, and in order to better design the end effector, the physical characteristics of the ginkgo spica and the ginkgo tree branch need to be analyzed, and the physical characteristics mainly comprise the aspects of geometric size, shape, quality, mechanical property and the like.
1.1 geometric characteristics of Ginkgo spica
The design of the end effector is based on ginkgo spica, and the determination of the mechanical characteristics and the mechanism size of the end effector both need to meet the geometric characteristics of the ginkgo spica.
Collecting branches of mature ginkgo spica, using the spica of a short branch as a group of data, wherein the number of the spica and the number of leaves of each short branch are different.
Because the sizes of the flower spikes and the leaves of the gingkoes of different short branches are different, the branches of different gingkoes are collected, and 100 groups of data are measured. The length and the maximum diameter of the flower spike are required to be measured in the experiment, and the ginkgo flower spike is spindle-shaped, the volume of the ginkgo flower spike is small, and the flower spike body is also fragile, so the ginkgo flower spike is directly measured by a ruler in the experiment. During the measurement process, the thicknesses and lengths of different short branches of ginkgo branches are different, so that the flower spikes and leaves on the long short branches are more, and the leaves are more mature. The thickness of the short branches is also one of the important factors influencing the structural design of the end effector; therefore, more experiments are performed as much as possible, and the experimental objects come from different ginkgo trees and different branches as much as possible, so that the universality of the experiments is improved, and the accuracy of the experiments is improved.
Statistics show that the length of the ginkgo biloba tassel is generally between 24mm and 27mm, the maximum diameter is generally between 5mm and 7mm, and data support is provided for the design of a finger clamping mechanism of an end effector. The number of the spica on each short branch is 4-6, and a plurality of blades are also arranged, and as the spica blades grow irregularly on the short branches and are difficult to position, the end effector cannot pick one spica at a time, the spica and the blades on the whole short branch need to be swallowed completely, and the spica and the blades can be distinguished through the force required by picking, so that the picking efficiency can be greatly improved.
1.2 spacing of the short branches of Ginkgo biloba
The spacing between the ginkgo biloba braches determines the diameter of the opening of the oral cavity gripping mechanism of the end effector, so the spacing between the braches needs to be measured. When adjacent short branches are not on the same horizontal plane, when one short branch is picked, the position and the angle of the insect body need to be adjusted, so that the picking efficiency is low, and therefore, when the end effector picks, the short branches with the included angle of less than 45 degrees on the similar plane are preferentially picked. During the experiment, the short branch distance of the ginkgo with the included angle of the adjacent planes less than 45 degrees is measured.
According to statistics, the distance between the short branches with the included angle of less than 45 degrees on the adjacent planes is about 80mm-100mm, so when the end effector starts picking up the spica on one short branch, the oral cavity can not interfere with the adjacent spica in the process of opening and closing, the radius of the maximum opening range of the end effector also needs to be less than 100mm, meanwhile, in order to ensure that the spica blades on the short branches can be swallowed into the oral cavity, the radius of the minimum opening range of the end effector needs to be more than 30mm, and the opening radius of the oral cavity of the end effector is 30mm-100mm in conclusion.
1.3 mechanical Properties of Ginkgo spica and leaves
The oral cavity part of the end effector mainly has a swallowing effect, the flower spike is picked after the flower spike of ginkgo is swallowed, the force for picking the flower spike needs to be measured, 3-5 flower spikes are arranged on each short branch of ginkgo branches cut during the experiment, 4-6 ginkgo leaves are arranged on each short branch, the interference of the picked leaves on the picking of the flower spike of ginkgo is reduced, the damage to the leaves is reduced as much as possible, and the force for picking the leaves of ginkgo is measured at the same time.
The flower ears and the leaves grow on the short branches, the end effector inevitably contacts the short branches when picking the flower ears, and the force required for breaking the short branches is measured in order to prevent the end effector from pinching the short branches when closing the end effector.
The stretching test was carried out by using a flat type, in which the picking force of 100 ginkgo biloba ears and leaves was measured by using a force gauge. The experimental instrument for measuring the pulling force is an ALIPO digital display push-pull dynamometer, and the model is as follows: ZP-500, Range: 500N, minimum reading: 0.001N.
The digital display tension meter is used for measuring 100 groups of data by matching with computer software. Statistics show that the force for picking the ginkgo spica is 0.8N-1.3N, the force for picking the leaves is 3N-4.3N, the force for breaking the short branches is more than 20N, the leaves cannot be damaged as much as possible when the ginkgo spica is picked, and the short branches cannot be broken by an end effector, so that the minimum force for picking the leaves is about 3N, the force for picking the spica is required to be less than 3N, and the minimum force for picking the spica is about 1N. When the end effector grips a short limb, the force applied to the short limb must be less than 20N.
2. Scheme design
The invention designs an end effector oral cavity part which simulates the predation of the bobit insects by utilizing bionics.
The bobtish is able to accurately and efficiently hunt for its sharp and powerful mouth. The mouth of the Bobitis insect is provided with a mouth device without muscle, and the mouth device is a hook claw with sharp two sides and is like a sickle with a plurality of petals. After catching the prey, the hook claw can tightly bite the prey, after killing the prey, the oral cavity of the mackbrood can suck the prey, and the prey can be fed into the oral cavity by continuously turning the hook claw inwards and outwards.
By simulating the head structure of the Bobitis insect, the oral cavity of the end effector designed by the invention mainly has three functions of occluding the spica, separating the spica and swallowing the spica.
(1) Occlusion function: by simulating the Bobitis insect and designing the occlusion mechanism of the outlet cavity, the flower spike can be accurately occluded and wrapped;
(2) separation function: the prey is swallowed by imitating the Bobtish to grasp the prey and turning over the prey from outside to inside by using a claw, and the spica is separated from the short branch after the end effector is designed to be occluded in the oral cavity to wrap the spica, so that the separation function is realized;
(3) swallowing function: the prey is swallowed into the body through the throat by imitating the Bober worm, and the throat is in a hollow tube shape, so that food is prevented from being blocked at the throat; therefore, the separated spica enters the collecting box from the pipeline in the oral cavity through the insect body, and the internal part of the oral cavity has no barrier to prevent the spica from entering the insect body of the end effector.
2.1 design of end effector oral configurations
The configuration of the oral cavity of the end effector is mainly determined by the occlusion structure, the first action of picking up the flower spikes in the oral cavity is occlusion, and the configuration is determined by the characteristics of the flower spikes. The ginkgo spica shape is similar to a spindle body, the size is very small, and the stem of the spica is fragile, so that the oral cavity of the end effector can better wrap all spica and blades on the short branches in the occlusion process, the contact area between the occlusion mechanism of the end effector and the spica blades can be increased, the pressure on the spica is reduced, the grabbing force can be better controlled, meanwhile, the blades and the short branches are protected from being damaged, and the end effector is prevented from being scraped by branches in the moving process.
The end effector oral occlusion mechanism is designed to be of a rotary type. The result of the mechanical property measurement of the flower spike and the leaf blade shows that the force for picking the flower spike is about 1N and the force for picking the leaf blade is about 3N, and the force required by the leaf blade is 3-4 times of that of the flower spike but is very small. The rotary structure can adjust the switch closing angle of the mechanism and has a larger meshing range. The occlusion mechanism is designed to be a rotary structure, and the oral cavity of the end effector can be designed to be a structure with more than two fingers (such as three fingers), so that the occlusion mechanism can better occlude and wrap the flower ears and the blades without damaging the blades and the short branches. Although the swivel structure is more complicated than the translation type and causes some errors of engagement, these errors can be compensated for by the control.
Therefore, the end effector oral occlusion structure designed by the invention is designed into a joint-free rotary cambered surface mechanism.
2.2 design of the way of separating the flower spike
The slewing mechanism for realizing occlusion of the oral cavity of the end effector is characterized in that after the occlusion fixation of the flower spike and the blades is finished, the next action is to separate the flower spike from the short branch in a combing and brushing mode, a structure similar to a brush is arranged in the oral cavity of the end effector, and after the flower spike is occluded, the brush is driven to brush the flower spike from the short branch.
The invention relates to an end effector of a picked ginkgo flower spike, which is different from vegetables and fruits, has very small size and weight, adopts a three-finger mechanism for better wrapping and fixing the flower spike by an occlusion mechanism, and separates the flower spike by a device adopting a combing and brushing principle on the mechanism.
The number of the oral joints of the end effector is related to the grabbing effect, if the number of the joints is more, the degree of freedom of the occlusion structure is more, the action is more flexible, and the grabbing effect is better. However, more joints are needed, more driving devices are needed, the more complicated the structure of the end effector is, the higher the control difficulty is, and meanwhile, the comb structure is arranged in the end effector, so that the oral cavity of the end effector is designed to have 1 degree of freedom.
2.3 design principles of end effectors
The invention researches and designs a mechanical oral cavity part scheme research of a ginkgo spica picking end effector, and the principle when the oral cavity structure of the end effector is designed comprises the following steps:
(1) the mechanical structure of the oral cavity of the end effector has certain sealing performance
The whole end effector picks up the spica from the short branches, and after the spica is fed into the oral cavity, because the ginkgo spica is 20-30 mm in size and very small, a protective cover (occlusion cover) fixed in occlusion is needed, so that the spica cannot fall off from the oral cavity when the oral cavity of the end effector picks up the spica, and the picking efficiency of the end effector is improved.
(2) Rationalization of a drive arrangement providing power to an end effector
Because the force required for picking the ginkgo spica is very small, the grasping force of the end effector is somewhat accurate in order to keep the leaves and short branches as far as possible from being damaged, which may require the use of a reducer to reduce the force transmitted by the drive means to the required magnitude. Secondly, the force for opening and closing the end effector is provided, and the stability of grabbing is ensured.
(3) The mechanical structure of the end effector needs to have sufficient strength and stability
Gingko branches are numerous and disordered, and the end effector can collide some small branches at any time in the picking process of the spica, so that the mechanical structure of the end effector has enough strength and stability, picking work can be still finished when some unavoidable collisions occur, and the end effector cannot be damaged.
2.4 end effector drive scheme
The pneumatic driving device drives the actuator to move by using the pressure of compressed air, and generally uses an air compressor as a power source. The pneumatic driving device has high safety and simple structure. By adjusting air pressure, stepless speed regulation can be realized, but the working speed is poor in stability, the device is large, the positioning precision is not high, and the ground grabbing force is small.
The invention sucks the picked ginkgo spica into a storage container in an air suction mode, adopts an air pressure driving device, so that an end effector is also driven by air pressure, and the invention mainly uses two pneumatic driving devices: a cylinder and an air motor. The pneumatic motor can not leak electricity and generate electric sparks in the working process, pollen is exploded when the flower spikes are picked, the end effector is in a dust environment, the pneumatic motor can not explode, and the pneumatic motor is safe even in an air humid environment. The pneumatic motor can work for a long time and has the performance of overload protection; the pneumatic motor has small volume, light weight and small power per unit size, can realize stepless speed change by adjusting air pressure, and can be installed in an end effector with small volume.
Drawings
FIG. 1 is a schematic flow diagram of the present design method;
FIG. 2a is a schematic structural view of an end effector oral cavity designed by the present design method;
FIG. 2b is a schematic view of another perspective of FIG. 2 a;
in the figure: the device comprises a clamping jaw 1, a clamping jaw base 2, an occlusion cover 3, a notch 4, a brush roller 5, a pneumatic motor 6, a cylinder 6, a cylindrical pin 7, a connecting rod head 8, a connecting rod seat 9, a funnel 10, a pipeline 11 and a connecting block 12;
FIG. 3a is a schematic view of a finger mechanism and gearing structure within the mouth of an end effector in a preliminary design;
in the figure: the device comprises a finger 13, a connecting rod 14, a connecting pull rod 15, a base 16, a pull cable 17 and a pull cable needle 18;
FIG. 3b is a schematic view of the configuration of the snap cap in a preliminary design;
FIG. 3c is a simplified schematic illustration of the configuration of the engagement of the snap cap with the finger in the initial design;
FIG. 3d is a schematic view of the configuration of the roller brush in the preliminary design;
FIG. 3e is a transmission diagram of the roller brush structure in the preliminary design;
in the figure: a roller brush 19, a conical gear 20 and a small-sized pneumatic motor 21;
FIG. 3f is a simplified external oral drive diagram of an end effector of improved design (bite cover fully closed);
FIG. 3g is a simplified oral external drive diagram of an end effector of improved design (maximum bite cover open);
FIG. 3h is a schematic view of a modified queen brush roll;
FIG. 3i is a schematic view of a modified brush roll mounting;
FIG. 3j is a schematic diagram of the funnel;
FIG. 3k shows the bite cover in an open position facing the tassel (end effector mouth facing the tassel);
FIG. 3l shows the bite cover facing the biting tassel (end effector mouth facing the tassel);
fig. 3m is the initial state of the bite cover (end effector mouth facing obliquely to the tassel);
fig. 3n is a fully occluded tassel state (end effector mouth facing tassel);
FIG. 3o is a force diagram of the end effector oro-occlusal shield in contact with the prong;
FIG. 4a is a schematic diagram of a model in a ROS environment;
FIG. 4b is a schematic view of an end effector in an initial state;
FIG. 4c is a schematic view of the end effector fully wrapped around the tassel;
FIG. 4d is a schematic view of the end effector in an initial state with an included angle with respect to the short branch different from 0;
fig. 4e is a schematic view of the engagement state of the end effector with the short limb at an angle different from 0.
Detailed Description
The design method is further described below with reference to specific embodiments:
end effector oral cavity structure design
In the picking process, the mechanical arm drives the end effector to move to a designated position, and the end effector grasps a specific ginkgo tree branch through a mechanism simulating a mouth tool; then the insect body section imitating mechanism of the end effector moves to approach the short branch; finally, picking the ginkgo spica by the oral cavity of the end effector to finish the whole picking process.
1 preliminary design of end effector oral Structure
1.1 finger and Transmission design
The inner part of the oral cavity of the end effector is designed with a finger structure similar to an endoskeleton, the inside of the oral cavity of the end effector is connected with a transmission mechanism, three fingers are connected through the transmission mechanism, the finger structure is equivalent to a rotary structure, and as shown in figure 3a, the finger structure and the transmission mechanism in the oral cavity of the end effector are simplified, and the finger structure consists of fingers, a connecting rod, a connecting pull rod, a base, a pull cable and a pull cable needle. The grabbing and clamping of the finger mechanism in the oral cavity of the end effector is the first step action of the whole oral cavity mechanism, and only when the flower spikes and the leaves are grabbed, the subsequent picking action can be carried out.
The end effector finger mechanism and the transmission mechanism are composed of an execution part and a driving part, and the driving part is composed of an air cylinder and other related components; the cylinder drives the inhaul cable, the inhaul cable needle is driven to move through the inhaul cable, the inhaul cable needle and the connecting pull rod move up and down together, and therefore the single connecting rod is driven to move, the connecting rod is pulled downwards, the three fingers are closed, and otherwise, the three fingers are opened. The executing part consists of three fingers, the size and the shape of each finger are the same, the included angle between every two fingers is 120 degrees, and the executing part is connected to a base. As can be seen from fig. 3a, the ends of the fingers are connected to the base through the pin, the middle of the fingers needs to be connected to a middle connecting rod through a connecting rod, and the movement of the connecting rod is controlled by the up-and-down movement of the connecting rod, so that the opening and closing movement of the fingers can be controlled. The finger mechanism is driven by the same cylinder, so the three fingers must move synchronously.
1.2 occlusion mechanism design
The part of the cavity of the end effector needs to be occluded and fixed by the occlusion mechanism before the spica is separated, and in order to ensure that the dropped spica cannot fall off from the end effector in the process of separating the spica, otherwise, the picking efficiency is reduced, the occlusion mechanism is designed into an occlusion cover mode. As shown in fig. 3b, the structural diagram of the occlusion cover is a simple arc surface similar to an ellipse, so the occlusion cover is not designed to be flat similar to a pincer, because the ginkgo spica is a spindle, the leaves are also curled, and the elliptical cover surface can adapt to the growth distribution of the spica on different short branches and reduce the damage of occlusion to the leaves when occluding the spica.
Each finger of the three-finger mechanism is connected with an occlusion cover, as shown in fig. 3c, the structural diagram of the connection between the occlusion cover and the finger is shown, the occlusion cover and the finger are connected by a slider-crank structure, the tail end of the occlusion cover is installed on the base and connected by a pin shaft, when the finger is pulled by the connecting rod, the occlusion cover moves together with the finger through the slider-crank structure, and when the slider moves to the highest point, the occlusion cover is in a completely closed state; when the slide block moves to the lowest point, the occlusion cover is in the maximum opening state, and the maximum opening range of the occlusion cover is determined by the moving range of the slide block. Because the mouth of the end effector can be opened and closed under-actuated, the three occlusion covers can only be opened and closed simultaneously.
1.3 comb structure design
The structure that the cavity part of the end effector separates the spica from the short branch utilizes the principle of combing and brushing. There are two alternative types of combing: one is a flat brush, the other is a roller brush, if the flat brush is adopted, two brushes are needed and are arranged in parallel, and the working principle is as follows: the tail end of each brush is driven by an air cylinder, the two brushes clamp the flower spike and move up and down continuously, and the brush hairs rub the flower spike to separate the flower spike from the short branches.
Each short branch of ginkgo has 4-6 spica and 4-6 leaves, but the moving speed of a cylinder piston is slow, so the up-and-down running frequency of the flat brush is low, and the working efficiency of separating the spica is low; and two more cylinders need to be installed on the end effector, so that the overall mass is increased, and a rolling brushing mode is adopted in a better mode. Referring to fig. 3d and 3e, a roller brush as shown in fig. 3d is installed at the end of each finger, a roller brush is installed on each finger, and after the snapping cover wraps the flower ears, the three roller brushes rotate together to brush the flower ears off the short branches to complete the separation.
The force required for picking the ginkgo spica and the ginkgo leaves is different, the ginkgo spica and the ginkgo leaves can be distinguished by controlling the rotating speed of the roller brush, the length of the brush and the material of the brush in the running process of the rolling brush, and the design is an end effector which has the principle of ensuring that the ginkgo spica is brushed down as far as possible, reducing the ginkgo leaves to be brushed down, and avoiding damaging the ginkgo leaves and the short branches as far as possible. As shown in fig. 3e, the driving diagram of the roller brush structure is shown, because the end effector is integrally selected to be the pneumatic driving device, the pneumatic motor is selected to drive the roller brush to rotate, and the rotational speed of the pneumatic motor can be controlled by adjusting the pneumatic pressure, so that the control is simple. According to the finger structure and size requirements, a pneumatic motor meeting the specification is selected.
2 the structural design of the oral cavity of the end effector is perfect
2.1 improvement of the drive Structure
In the preliminary design scheme of the oral cavity of the end effector, the transmission structure is arranged in the oral cavity, and a plurality of small parts are concentrated in the oral cavity. In the actual picking process of the ginkgo spica, the roller brush separates the spica from the short branches, the spica cannot be complete, most of the spica is anther, and partial spica can directly explode pollen in the oral cavity, therefore, the interior of the oral cavity of the end effector can be in a dust environment, and in addition, the air suction mode is adopted for swallowing and collecting the spica, the spica and pollen can be remained in the pin shaft hole, the connecting pull rod hole and other tiny parts in the work, along with the continuous work of the end effector, the anther and pollen remained in each joint in the oral cavity are continuously accumulated, the connecting rod transmission structure and the crank slide block structure can be clamped, the oral cavity of the end effector can not normally run, and the oral cavity of the end effector needs to be cleaned once every a period of time, but can affect the efficiency of the end effector and can also cause damage to the end effector structure.
Therefore, the inside of the mouth cavity of the end effector does not need to be of a complex structure as much as possible, and the transmission mechanism is designed outside the occlusion cover, and a simplified transmission diagram of the outside of the mouth cavity of the end effector is shown in fig. 3f and 3 g. The improved end effector consists of an occlusion cover 3, a connecting rod, a (small) cylinder 6, a connecting rod seat 9 and a clamping jaw base 2. The occlusion cover is connected with one end of a connecting rod through a cylindrical pin, the other end of the connecting rod is connected with a piston of a cylinder, the bottom of a cylinder seat of the cylinder is connected with a connecting rod seat, the connecting rod seat is fixed on a clamping jaw base, the cylinder seat is connected with an air pipe and is communicated with certain air pressure, a piston rod is pushed to move, and the piston rod pushes the connecting rod to control the occlusion cover to perform closing movement.
Figure 3f shows the snap cap fully closed, with the length of the snap cap being about 105mm, and the maximum stroke of the cylinder piston rod being about 22 mm. Fig. 3g shows the maximum opening range of the occluding cover, and the maximum opening radius of the occluding cover is 30mm-100mm according to the distance between the adjacent short branches with the included angle of less than 45 degrees of the adjacent planes, as can be seen from the figure, the radius of the base is 50mm, and the included angle between the maximum opening range of the occluding cover and the horizontal plane is about 56 degrees, so that the maximum opening radius of the occluding cover can be about 78 mm.
The driving device of the improved front transmission mechanism only has one air cylinder, can simultaneously control the opening and closing of the three occlusion covers, and the selected air cylinder has larger cylinder diameter and weight and is difficult to adjust air pressure; the optimized end effector is driven by 3 cylinders, each occlusion cover is connected with one cylinder, and the cylinders can be driven synchronously or independently.
The three occlusion covers can only be controlled to move simultaneously by driving of one air cylinder, if the oral cavity is not directly opposite to the flower spike for picking, two occlusion covers are bound to clamp the short branch in the process of occluding the flower spike, the occlusion covers cannot be occluded continuously in order to avoid damaging the short branch, at the moment, the third occlusion cover does not completely cover the flower spike, and the flower spike cannot be separated from the short branch by operating the rolling brush under the condition. Under the same condition, each occlusion cover can move independently, even if the flower spikes are clamped, the occlusion covers cannot be closed continuously, and the other occlusion cover can still move continuously until the flower spikes are completely occluded.
Although three cylinders are required to be installed after improvement, the whole weight of the end effector is increased, the end effector has stronger self-adaptive capacity for picking the flower spikes, can pick at multiple angles, and has better picking effect compared with under-actuation.
2.2 Structure improvement of rolling brush and pneumatic motor
The roll comb is the mechanism that realizes the separation spica function, the round brush combing hair of preliminary design is shorter, although end effector is holding the spica in the parcel that interlock cover can be firmly when just facing the spica, the contact spica that the round brush can be fine, the cylinder brush can just begin the combing and brushing spica, but the spica and the blade quantity of different short branches are different, spica and blade are inhomogeneous, spica and blade distribution, three round brush can be brushed spica and blade, but the more short branch of some spica blades, the round brush hair can only contact the spica, the inside spica brush can not arrive, and when picking the less short branch of spica blade, the idle phenomenon of round brush can appear even, so the brush hair of round brush must have sufficient length. The end effector picks from other directions, the closing range of the occlusion cover is smaller, the included angle between the rolling brushes is more than 30 degrees, and the flower spike separation can be better completed only if the bristles are longer.
As shown in fig. 3h, which is a schematic view of an improved rear roller brush, bristles of the roller brush can be in a passive and flexible manner, so that the occlusion cover and the roller brush mechanism have a certain self-adaptive capacity to the grabbed flower spikes and blades. After improvement, a roller brush and an air motor are directly installed on the occlusion cover, the finger structure is optimized and removed, so that a larger space is formed in the occlusion cover to accommodate the brush, and short branches with more spica and blades can be picked, after the finger structure is removed, the weight of an oral cavity mechanical mechanism of the end effector can be reduced to a certain extent, and the overall weight of the end effector is reduced, as shown in a figure 3i, the air motor and the rolling brush are directly installed on the occlusion cover.
The length of the flower spike and the blade body on the short branch is different, the length of the stem of the short branch is different, so in order to ensure that all the flower spikes can be sufficiently combed, the shaft of the roller brush is vertically placed, the length of the roller brush can be increased, the flower spike can be subjected to all-directional rolling brushing, the occlusion cover can prevent the left and right brushing modes, the flower spike is not brushed out of the end effector, the selection is vertical, and the bristles are long enough and elastic.
2.3 design of intraoral swallow Structure
The end effector lumen portion designed herein requires the final task of swallowing after the act of separating the tassel is completed. In the embodiment, the flower spikes are sucked into the collecting box from the oral cavity through the insect body of the end effector by an air suction method, the swallowing structure is designed into a funnel device, the structural sketch of the funnel device is shown in fig. 3j, on one hand, the funnel structure is more beneficial to air suction, and the efficiency of swallowing the flower spikes can be improved; on the other hand, the narrow end of the funnel is used for connecting the first worm body section of the end effector.
"oral cavity" and "worm body" connection structure are the first festival of the end cover-in worm body with the funnel to the upper surface of the first festival of worm body and the lower surface coincidence of funnel, two structures are inside all to open has a keyway, and is fixed through the key, prevents to rotate, is fixing worm body and funnel end through bolted connection.
The working principle of the cavity part of the end effector designed by the embodiment
The oral cavity of the end effector has two working conditions:
(1) the oral cavity of the end effector is directly opposite to the flower spike for picking, the insect body of the end effector sends the oral cavity to the position right close to the flower spike, the occlusion covers are in an initial opening state as shown in figure 3k, then the air cylinder is started, the piston rod starts to operate, the three occlusion covers are simultaneously driven to occlude until the oral cavity completely occludes the flower spike as shown in figure 3l, then the pneumatic motor is started to drive the rolling brush to rotate, the flower spike starts to be separated, and meanwhile, the air suction device is started to suck the separated flower spike and anther into the collection device.
(2) The mouth of the end effector is inclined to the flower spike for picking, the included angle between the axis of the mouth and the short branch is 0-45 degrees, as shown in fig. 3m, the mouth axis and the short branch are inclined to the flower spike, as shown in fig. 3m, the bite cover is in an initial open state, and the included angle between the axis of the mouth and the short branch is about 40 degrees. When the end effector occlusion covers are inclined to occlude the flower spike, the two occlusion covers close to the branches can clamp the short branches in the closing process, at the moment, the two occlusion covers can not be closed, and the third occlusion cover is continuously closed until the flower spike is completely occluded as shown in fig. 3 n. Then the work of separating and separating the spica and swallowing is finished.
After the flower ears on the short branches are picked, the air suction device and the rolling brush stop operating, the air cylinder opens the occlusion cover and prepares to pick the flower ears on the next short branch.
3 end effector oral mechanics analysis
The design objective of the present invention is to provide a mechanical design scheme for the oral cavity portion of the end effector, where the most important requirement is to achieve the separation of the tassel from the grafted male ginkgo while ensuring that the short branches are not damaged and the leaves are less damaged. The end effector is controlled to pick ginkgo spica, and the force provided by the driving device is controlled without damaging the leaves and the short branches.
3.1 mechanical Properties of the Rolling Brush and model selection of the pneumatic Motor
The roller brush (i.e. brush roll) is the most important part for separating the ginkgo spica from the short branches, and the brush hairs of the roller brush are made of soft and elastic materials so as not to damage the blades. In order to fully brush all the spica on the short branches and improve the picking efficiency, the brush bristles of the brush are longer, so that the condition that the roller brush idles and cannot finish picking due to too short brush bristles is prevented; because the number of the flower spikes and the number of the blades on different short branches are different, the brush hair is longer and has certain elasticity, and the roller brush can have shape self-adapting capability to the grabbed flower spikes and the grabbed blades by a passive and flexible mode.
In the present embodiment, a small-sized air motor is selected as a driving device of the roll brush, and as shown in table 1, the table is a parameter table of the air motor.
TABLE 1 pneumatic motor parameter table
The minimum force required by picking ginkgo leaves is about 3N, the length L of the rolling brush is 5cm, the shaft diameter D is 1cm, and the radius R of the whole rolling brush is 2 cm. Because the bristles are soft and have certain deformability, the bristles can be damaged along with the working time, and the minimum force for brushing the blades by the rolling brush is set to be F0＝3N。
T＝F×r (3-1)
The shaft radius r of the air motor of the present embodiment is 5mm, and is obtained by the formula (3-1),
t is 0.015 N.m, and the rated torque of the pneumatic motor is 0.012 N.m, which meets the requirement.
3.2 analysis of dynamics of occluded cover on short branches of end effector and cylinder model selection
The end effector occlusion cover picks up the short branches in the direction opposite to the direction of the flower spikes, so that the short branches can be clamped by the occlusion cover, but the short branches cannot be clamped by the occlusion cover, so that the dynamic analysis of the end effector occlusion cover on the short branches is required.
In order to reduce the overall mass of the end effector, a small cylinder with a 16mm bore diameter was chosen, which, as shown by the parameters in table 2, provides a torque of 0.16N · m at a pressure of 0.5 MPa.
TABLE 2 Small Cylinder parameter Table
FIG. 3o shows the force diagram of the end effector oral cavity occluding cover contacting the short limb, where CD clamps the short limb for the occluding cover, AB is a cylinder and a piston rod, A, C is fixed on the base of the occluding cover, the cylinder pushes the occluding cover to close and the cylinder AB is at the same time, so the cylinder drives the force F0Output torque M to the meshing cage DE. Distance of AC is l1Approximately 8.6cm, the length of AB is l2About 4.5cm, and AB length of l1Approximately equal to 8.2cm, the length of BC is l2About 7.5cm, BD length of l3Approximately equal to 3cm, and the included angle between the cylinder AB and the occlusion cover is theta0. When the occluding cover contacts the short branch, the point D of the occluding cover is subjected to the reaction force F of the short branch.
Preliminarily, the end effector is assumed to be made of hard aluminum, and the mass of the cylinder AB is m1Approximately equals 1.2kg, and the mass of the occlusion cover CD is m2≈0.3kg
Because the occlusion cover CD is powered by the cylinder AB, the virtual displacement delta theta is generated at the moment when the occlusion cover contacts the short branch, and the virtual displacement at the point B is
δSB＝l2δθ (3-2)
The engaging cover CD is subjected to the gravity of m2g, the virtual displacement in the action direction is
Then cylinder AB gravity m1The virtual displacement under the action of g is
The virtual displacement of the applied force at point D is
From the principles of imaginary work, equations can be derived
Mδθ+m1gδO1+m2gδO2＝FδSD (3-6)
δ S is equally divided on both sides of formula (3-8)DCan obtain the product
By bringing the compounds of the formulae (3-2), (3-3), (3-4) and (3-5) into (3-7), a compound of the formula
Will l2≈7.5cm，l3＝3cm，θ028 degree embedded type (3-8)
Output torque M ═ F0l0 (3-9)
The cylinder providing a pressure of F0＝PS＝500000×0.004×0.004×3.14＝25.12N
F is to be0＝25.12N，l0About.0.5 cm into (3-9)
M＝F0l0＝0.1256N·m
M is to be1，m2The value of M is brought to F ≈ 15.2N in formula (3-8),
the force required by the short branch breaking is 20N, F is approximately equal to 15.2N and is less than 20N, so that the cylinder is selected, the force is lower than 20N when the occlusion cover clamps the short branch, the short branch cannot be clamped, and the design requirement is met.
4 end effector oral cavity mechanism picking simulation test
4.1 construction of simulation platform
The ROS is an open source robot operating system released by Willow Garage in 2010, adopts a distributed architecture, realizes hierarchical operation of tasks by transmitting messages through nodes (nodes) with independent functions, and has the advantages of supporting multiple languages, being free and open source, being easy to expand codes and the like. ROS is generally not applicable in Windows systems, and requires installing Ubuntu virtual machines, here using Ubuntu20.04 version, in the original Windows systems of computers, and installing and using ROS in virtual machines. The embodiment mainly carries out simulation test on the designed cavity part of the tail end executor through the ROS.
4.2 creation of end effector mouth model in ROS
4.2.1 creation of three-dimensional models of the end effector mouth
As used herein, the SolidWorks2018 version creates a three-dimensional model that simplifies the structure of the end effector oral cavity, without the drive and roller brush structures of the oral cavity structure being assembled, but only the bite cover, base and funnel of the end effector, in order to enable successful introduction of the end effector oral cavity into the ROS.
4.2.2 URDF model File
URDF is an XML language that uniformly describes the settings of a robot simulation model. Data in the URDF file is needed during simulation, and ROS Moveit is imported for simulation. Before the ROS is introduced for simulation, a SW2.urdf file is required to be downloaded and installed in a Data folder of SolidWorks to serve as an auxiliary tool, and then a modeled model is edited again, and all objects in simulation software need to be positioned and defined in the SolidWorks.
Before generating the URDF file, a coordinate system and a reference axis need to be added in the whole three-dimensional model of the end effector, and when the coordinate system in the SolidWorks is converted into the URDF file, corresponding coordinate points are generated, wherein the coordinate points are the positions and the directions of the joints of the three-dimensional model relative to the coordinate system in the ROS simulation environment; the reference axis is associated with the three-dimensional model and the joint rotation. According to the design, a coordinate system needs to be established in the oral cavity part of the end effector, a coordinate system needs to be established in each occlusion cover, a reference shaft is needed in the opening and closing rotary joint of each occlusion cover, a coordinate system is needed in the middle of the inside of the oral cavity of the end effector, and 4 coordinate systems and 3 reference shafts are needed in the oral cavity of the whole end effector.
The URDF model file contains a series of joints and links, as shown in fig. 4a, and the complete end effector oral structure is composed of many joints and links, which contain various attributes of the three-dimensional model. Wherein the join is used for connecting two objects, and represents a relative motion form between the two objects, position information of joint motion and the like, and the motion types comprise a rotary joint, a stretching joint, a sliding joint, a floating joint and the like. Link is information describing the shape, size, color and the like of each model of the three-dimensional model, two models connected by Link must specify that one of them is a parent Link and the other is a child Link, and the positional relationship of the child Link must depend on the parent Link. In the model introduced by the paper, the occlusion cover is a connecting rod, and the part of the base connected with the occlusion cover is a joint.
The end effector can simulate picking of the spica in a simulation environment, a spica model is required to be led in, the spica model is that two short branches are arranged on one small branch, 4 spica are arranged on each short branch, the spica model is converted into a URDF file, and the URDF file is led into the ROS Moveit.
Simulation test
The URDF file is imported into the ROS Moveit, the model file is opened in the file directory, an instruction roslaunch sc _ gaebo launch is input at the ROS terminal, and the oral cavity model and the flower spike model of the end effector are displayed through the Rviz, as shown in FIG. 4c, the model in the ROS environment. The ear model is shown as stationary and the end effector can rotate 360 about the central axis, translate along the center, and flip 180 about the center of the bottom of the funnel.
In fig. 4b, the end effector is in an initial state, and the central axis of the oral cavity and the short branches of the flower spike are on the same straight line, at this time, the included angle between the occlusion cover of the end effector and the horizontal plane is 56 degrees, and the distance between the plane where the tip of the occlusion cover is located and the short branches is 5 mm. Fig. 4c shows the flower spike completely wrapped and capable of separating the flower spike from the short shoot, and if the occlusion cover is completely closed, the flower spike interferes with the cover surface. The distance between the surface where the tip of the occlusion cover is located and the short branch is adjusted to 10mm in the initial state, the occlusion cover is controlled to be closed, the flower spike can be completely wrapped by the occlusion cover, and the flower spike can be separated from the short branch. And continuously adjusting the distance between the surface of the tip of the occlusion cover in the initial state and the short branch to 15mm, wherein the flower spike is not completely wrapped in the oral cavity by the occlusion cover in this case, and the flower spike cannot be completely separated from the short branch at the moment.
Therefore, the end effector is in an initial state, the distance between the plane where the tip of the occlusion cover is located and the short branch is 5mm-10mm as far as possible, otherwise, the occlusion cover cannot completely wrap the flower spike and the flower spike is still exposed out of the oral cavity due to the fact that the distance exceeds 10mm, and the rolling brush cannot complete the flower spike separation work.
When the included angle between the central axis of the end effector and the short branch is not 0, the flower spike needs to be occluded from the side surface of the short branch, the included angle between the central axis of the end effector and the short branch is adjusted to be 30 degrees, as shown in fig. 4d, the end effector is in an initial state when the included angle is 30 degrees, meanwhile, the distance between the occlusion cover and the branch needs to be adjusted to prevent interference, then, the occlusion cover is controlled to be closed, as shown in fig. 4e, the occlusion cover can completely wrap the flower spike, and the separation of the flower spike is completed.
The invention requires that the included angle between the central shaft of the end effector and the short branch can pick up ginkgo spica within the range of +/-45 degrees, so that the included angle between the central shaft of the end effector and the short branch is adjusted to be 45 degrees, at the moment, the short branch of the spica is clamped in the occlusion process of the occlusion covers, so that the angle of the third occlusion cover is adjusted under the condition that the two occlusion covers clamp the short branch without interference, and finally, the end effector can still wrap the spica and complete the separation of the spica under the condition that the occlusion covers do not interfere with the short branch, and the fact that the oral cavity of the end effector can separate the spica from the short branch within the range of +/-45 degrees is verified.
5. Conclusion
The invention provides a method for designing an end effector oral cavity for picking ginkgo spica by researching a picking end effector and the ginkgo spica. Through the analysis of the oral cavity structure of the Bobitis insects and the observation and research of the hunting process, three functions of occlusion, separation and swallowing of the oral cavity of the end effector are obtained, two structural design ideas are provided, comparison and perfection are carried out, a driving device is determined, a three-dimensional model of the oral cavity structure of the end effector is designed and established, the three-dimensional model can be assembled with the insect body and the oral cavity model of the end effector, then the oral cavity occlusion mechanism carries out dynamic analysis on short branches, and the separated spike mechanism carries out stress analysis on blades. And finally, establishing an ROS simulation environment, and carrying out picking simulation and performance test.
(1) The end effector separates the flower spikes through the rolling brush, and because of the flexibility of the brush hair of the rolling brush, the force for separating the flower spikes can be directly controlled by adjusting the rotating speed of the pneumatic motor, so that the damage to the blades can be reduced to a great extent while the flower spikes are separated.
(2) The invention adopts a plurality of drivers to control and pick the flower spike, each occlusion cover of the oral cavity can be independently opened and closed, and even if the flower spike is not directly opposite to the oral cavity, the end effector can accurately occlude the flower spike.
(3) The invention adopts an air suction mode to swallow the separated spica into a worm body (through a pipeline) and finally to suck into a collection box. The end effector oral swallow structure is designed to be funnel-shaped and is easier for air suction.
(4) The end effector for picking fruits and vegetables generally only has two fingers or clamping jaws, and the oral cavity of the end effector is provided with three occlusion covers, because the sizes and the qualities of ginkgo spica are very small, and each short branch is provided with a plurality of spica, the three occlusion covers can better wrap the ginkgo spica and can not easily damage leaves.
The picking end effector is specially used for picking ginkgo spica, is used for grafting male plant ginkgo in a plantation, can carry out picking work in a large area, and has certain picking efficiency. The end effector structure function applies bionics, imitates the oral cavity structure and the occlusion action of the Bobitis insect. Through the mechanical analysis of the occlusion cover and the rolling brush, short branches and flower spikes are prevented from being damaged in the flower spike picking process.
In the simulation process, the fact that the end effector is close to the spica along the central axis of the end effector is verified, and when the included angle between the target spica short branch and the central axis of the end effector is +45 degrees, the oral cavity of the end effector can successfully separate the spica from the short branch. When the end effector is opposite to the flower spike, the distance between the plane of the tip of the occlusion cover in the initial state of the end effector and the short branch is within the range of 5mm-10mm, the oral cavity can wrap the flower spike, so the flower spike can be separated from the short branch. The design requirements of the total end effector are met.
Referring to fig. 2a and 2b, the design method of the embodiment designs an end effector oral cavity for picking ginkgo flower spikes, which comprises a clamping jaw 1 and a clamping jaw base 2; the clamping jaws are the same in number and are symmetrical around a straight line l;
the bottom of the clamping jaw 1 is rotatably connected to the clamping jaw base 2, and the rotating axis is vertical to the straight line l; the clamping jaw is driven to rotate by a first driving mechanism;
the clamping jaw 1 comprises an occlusion cover 3 and a separation mechanism; the top end of the occlusion cover 1 is provided with a notch 4, and the separating mechanism is arranged on the inner side of the occlusion cover;
the state formed by the rotation of each clamping jaw 1 is divided into a closed state and an open state; in a closed state, the side edges of the occlusion covers of the adjacent clamping jaws are attached, each occlusion cover encloses a hollow cavity, and the gap 4 of each occlusion cover 1 encloses a through hole;
the separating mechanism is a brush roller 5, and the brush roller is driven to rotate by a second driving mechanism.
The clamping jaw is 3. The bite cover is part of a spherical cap-like shape.
The clamping jaw base 2 is cylindrical, the front end opening of the clamping jaw base is communicated with the hollow cavity, and the rear end opening of the clamping jaw base is connected with the pipeline 11; the axis of the clamping jaw base coincides with the straight line l; under the closed state, the bottom edge of the occlusion cover of each clamping jaw is attached to the top edge of the side wall of the clamping jaw base.
The first driving mechanism is a cylinder 6; the cylinder block of cylinder rotates to be connected in the outer wall of clamping jaw base, and the piston rod of cylinder rotates to be connected in the outer wall of interlock cover. Referring to fig. 1 and 2, in implementation, the outer wall of the jaw base 2 is connected with a connecting rod base 9; the cylinder seat of the cylinder 6 is rotatably connected with a connecting rod head 8 on a connecting rod seat 9 through a cylindrical pin 7. In a similar way, the connecting rod head 8 at the top end of the piston rod of the air cylinder 6 is rotatably connected with the connecting block 12 outside the occlusion cover 3 through the cylindrical pin 7.
The brush roller 5 is formed by connecting nylon wires outside a plastic rod (PP rod), and the nylon wires are in a radial shape around the axis of the plastic rod; the second driving mechanism is a pneumatic motor 6, a rotor of the pneumatic motor 6 is connected with the plastic rod, and the pneumatic motor is connected with the inner wall of the occlusion cover; the axis of the plastic rod is coplanar with the line l.
Referring to fig. 2b, a funnel 10 is further connected between the rear end opening of the jaw base 2 and the pipeline 11; the big mouth one end of funnel 10 is connected with the rear end opening of clamping jaw base, and the osculum one end of funnel 10 is connected pipeline 11.