Automatic vibration reduction falling type fruit harvesting platform and control method

Abstract

The invention discloses an automatic vibration reduction falling type fruit harvesting platform and a control method. The harvesting platform comprises a movable chassis and a 4RRS rigid-flexible coupling parallel mechanism; the 4RRS rigid-flexible coupling parallel mechanism comprises a net stretching mechanical arm assembly and a flexible harvesting net; the net stretching mechanical arm assembly comprises a plurality of groups of harvesting mechanical arms and a driving unit; an end effector of each group of harvesting mechanical arms is connected with a flexible collecting net; each group of driving units comprises a brushless direct current motor, a driving plate, a rotary encoder and a current / voltage sensor; when fruits fall onto the flexible harvesting net from the high altitude, the impact force of the fruits can be locally stiffened through the flexible harvesting net and is transmitted to the harvesting mechanical arm; according to the control method of the falling type fruit harvesting platform with the automatic vibration reduction function, the 4RRS rigid-flexible coupling parallel mechanism is used in cooperation with fruit impact force identification and an automatic vibration reduction control algorithm, so that falling fruits can be stably, rapidly and nondestructively harvested, the harvesting success rate and the nondestructive rate are increased, and the labor intensity and the cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of automatic fruit picking, and particularly relates to a falling fruit harvesting platform with independent vibration damping and a control method therefor. Background Art

[0002] Falling harvesting is a method of harvesting fruits or fruits of medicinal plants by allowing the fruits to fall naturally when they are ripe. This harvesting method is mainly applied to those varieties of fruits that are easy to fall off the branches after ripening and can withstand a certain impact, such as oil-tea camellia fruits, durians, coconuts, jackfruits, etc. Taking the falling harvesting of durians as an example, in recent years, the durian industry has expanded rapidly with factors such as market demand, e-commerce, and policy support, which has further increased the demand for the automation of durian harvesting.

[0003] Durian, as a unique tropical fruit, is famous for its unique appearance and strong aroma. Its shape is an irregular sphere, usually 10-20 cm in length, with a dark green or yellow-brown outer skin, and many raised spikes are arranged on the surface. The sizes and densities of the spikes are different. Among them, the presence of the spikes also increases the difficulty of its harvesting. At present, there is no dedicated durian harvesting machine on the market, and the existing harvesting methods are usually divided into two types: the natural dropping method and the manual picking method, and these two picking methods have the following disadvantages:

[0004] Natural dropping method: It utilizes the characteristic that ripe durians will fall automatically. Since ripe durians are relatively heavy, directly hitting the ground may cause damage to the pulp. Therefore, it is necessary to lay a large-area net or blanket under the plants as a means of passive vibration damping (a similar method is also adopted for the harvesting of oil-tea camellia fruits) to catch the durians that fall randomly from the trees to ensure that the durians will not be damaged. However, the cost of laying a large-area net is high, and the requirements for the site are high, making it difficult to popularize among small and medium-sized growers.

[0005] Manual picking method: It requires two people to cooperate. One person climbs up the durian tree at a high place and cuts off the ripe durian. The other person uses a linen cloth to catch the falling durian under the durian tree. This method requires high skills and a lot of experience, and it is easy to cause the durians to be broken or damaged. Moreover, the spikes of the durians themselves pose a great safety hazard to the harvesting personnel under the durian tree.

[0006] Therefore, in the process of durian harvesting, whether it is the passive vibration damping of the natural dropping method or the manual active vibration damping of the manual picking method, falling harvesting requires vibration damping for the harvested fruits. Therefore, how to achieve efficient and safe vibration damping harvesting under the plants is the key problem restricting the yield, transportation, storage, and personnel safety of falling fruit harvesting. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the present invention provides a self-damping falling fruit harvesting platform, which can identify the magnitude and direction of the impact force when the fruit falls in real time, and achieve autonomous active damping, so as to realize the non-destructive harvesting of fruits.

[0008] The second object of the present invention is to provide a control method for a self-damping falling fruit harvesting platform.

[0009] The technical solution of the present invention to solve the above technical problems is as follows:

[0010] A self-damping falling fruit harvesting platform includes a mobile chassis and a 4RRS rigid-flexible coupled parallel mechanism arranged on the mobile chassis. Among them, the 4RRS rigid-flexible coupled parallel mechanism includes a net-opening robotic arm assembly and a flexible harvesting net; the net-opening robotic arm assembly includes multiple groups of harvesting robotic arms and multiple groups of driving units; the end effector of each group of harvesting robotic arms is connected to the flexible collection net; each group of driving units includes a brushless DC motor and a driving board for controlling the brushless DC motor. Among them, a rotary encoder and a current / voltage sensor are arranged on the driving board; the current / voltage sensor is connected to the armature winding of the brushless DC motor, and the motor torque of the brushless DC motor is calculated in real time by measuring the current / voltage and using the functional relationship between the current / voltage and the torque; the rotary encoder is coaxially connected to the output shaft of the brushless DC motor, and is used to detect the rotation angle of the brushless DC motor in real time, as well as the speed and acceleration of the rotation of the brushless DC motor.

[0011] Preferably, there are four groups of harvesting robotic arms, and the end effectors of the four groups of harvesting robotic arms are respectively connected to the four diagonals of the flexible harvesting net.

[0012] Preferably, each group of harvesting robotic arms is a two-degree-of-freedom rotating robotic arm; the two-degree-of-freedom rotating robotic arm includes a base, a lower swing arm, an upper swing arm, and an end effector arranged on the upper swing arm. Among them, a lower joint is arranged between the base and the lower swing arm; an upper joint is arranged between the lower swing arm and the upper swing arm; correspondingly, there are two groups of driving units in each group of harvesting robotic arms, and the two groups of driving units are respectively located at the upper joint and the lower joint in the two-degree-of-freedom rotating robotic arm, and are used to drive the upper swing arm and the lower swing arm in the two-degree-of-freedom rotating robotic arm to swing.

[0013] Preferably, the flexible harvesting net adopts a square flexible burlap net, and the flexible harvesting net is edge-sealed; connection parts connected to the end effectors of the harvesting robotic arms are arranged at the four diagonals of the flexible harvesting net.

[0014] Preferably, the mobile chassis is a tracked mobile chassis.

[0015] A control method for a falling fruit harvesting platform for autonomous vibration reduction, comprising the following steps:

[0016] Step S1: The mobile chassis transports the 4RRS rigid-flexible coupled parallel mechanism to the lower part of the plant where the fruit to be harvested is located; subsequently, each group of driving units controls the actions of each group of harvesting robotic arms to adjust the harvesting robotic arm to the initial state, thereby adjusting the attitude of the flexible harvesting net to the preparatory form before harvesting;

[0017] Step S2: When the fruit falls into the flexible harvesting net in a falling manner, the flexible harvesting net transfers the impact force of the fruit fall to the harvesting robotic arm, so as to cause the joints of the harvesting robotic arm to swing, thereby causing a current / voltage change in the armature winding of the brushless DC motor in the driving unit, and collecting the change value of the current / voltage through a current / voltage sensor;

[0018] Step S3: Construct a mathematical model for identifying the fruit impact force, input the change value of the current / voltage collected by the current / voltage sensor into the constructed mathematical model for identifying the fruit impact force, and obtain the magnitude and direction of the fruit impact force through the mathematical model for identifying the fruit impact force;

[0019] Step S4: The control unit formulates a corresponding vibration reduction harvesting strategy based on the magnitude and direction of the fruit impact force, generates a corresponding control command according to the formulated vibration reduction harvesting strategy, and thereby controls the movement trajectory of each group of harvesting robotic arms through the driving unit to drive the movement of the flexible harvesting net;

[0020] Step S5: When the vibration reduction harvesting of the fruit is completed, each group of driving units controls the coordinated movement of each group of harvesting robotic arms to cause the flexible harvesting net to pour the harvested fruit into the harvesting box;

[0021] Step S6: Each group of driving units controls the movement of each group of harvesting robotic arms to return to the initial state, and then repeats steps S2 - S5 to start the next round of fruit harvesting work.

[0022] Preferably, in step S1, there are four groups of the harvesting robotic arms, and the end effectors of the four groups of harvesting robotic arms are connected to the four diagonals of the flexible harvesting net; each group of harvesting robotic arms is a two-degree-of-freedom rotating robotic arm; the two-degree-of-freedom rotating robotic arm includes a base, a lower swing arm, an upper swing arm, and an end effector provided at the end of the upper swing arm. Among them, a lower joint is provided between the base and the lower swing arm; an upper joint is provided between the lower swing arm and the upper swing arm.

[0023] Preferably, in step S3, the steps of identifying the direction of the fruit impact force through the mathematical model for identifying the fruit impact force are:

[0024] Step S301: Taking the center of the flexible harvesting net as the coordinate origin, divide it into a first quadrant area, a second quadrant area, a third quadrant area, and a fourth quadrant area; then number the four groups of harvesting robotic arms.

[0025] Step S302: Compare the change values of the current / voltage of the brushless DC motors in the harvesting robotic arms collected by the current / voltage sensors in each group of drive units, determine the harvesting robotic arm with the largest change value of the current / voltage, and determine the quadrant area where the fruit falls on the flexible harvesting net according to the number of this harvesting robotic arm.

[0026] Preferably, in step S3, the process of the fruit impact force identification mathematical model for identifying the magnitude of the fruit impact force is as follows:

[0027] Step 311: During the process of the fruit impacting the flexible harvesting net, record in real time the current / voltage data of the brushless DC motors in the upper joints and lower joints of the four groups of harvesting robotic arms.

[0028] Step 312: Find out the moment when the current / voltage of the brushless DC motors in the upper joints and lower joints of each group of harvesting robotic arms first reaches the extreme value in the recorded current / voltage data, obtain the value of the current / voltage at this moment, and convert it into the corresponding motor torque according to the functional relationship between the current / voltage and the torque.

[0029] Step 313: Obtain the rotation angles of the brushless DC motors in the upper joints and lower joints of the harvesting robotic arms through the rotary encoder, thereby obtaining the postures of the harvesting robotic arms, and combining with the motor torque obtained in step S312, calculate the forces borne by the end effectors of each group of harvesting robotic arms. By performing vector summation on the forces borne by the end effectors of each group of harvesting robotic arms, obtain the magnitude of the fruit impact force.

[0030] Preferably, in step S4, the steps for specifying the vibration reduction harvesting strategy are as follows:

[0031] Step S401: Record in real time the current or voltage data that is the same as the change situation of the joint torque of the harvesting robotic arm.

[0032] Step S402: Make corresponding waveforms according to the recorded current or voltage data to detect the frequency and amplitude of the current or voltage in real time, so as to obtain the frequency and amplitude of the vibrations received by the four groups of harvesting robotic arms.

[0033] Step S403: The vibrations received by the four groups of harvesting robotic arms will have an impact on the motor torque of the DC brushless motors in the upper and lower joints of each group of harvesting robotic arms. Taking the generated motor torque impact as a known condition, the positions, angular velocities, and angular accelerations of the upper and lower joints in each group of harvesting robotic arms are calculated in real time using inverse kinematics. Combining with the inverse dynamics equation of Lagrange's second kind, the optimal reverse reaction torques that the upper and lower joints in each group of harvesting robotic arms need to generate to offset the received motor torque impact are calculated in real time. At the same time, control commands corresponding to the optimal reverse reaction torques are generated and sent to the drive units of each group of harvesting robotic arms, so as to prompt the brushless DC motors at the upper and lower joints of each group of harvesting robotic arms to output the calculated optimal reverse reaction torques, thereby driving the flexible harvesting net to move and reducing or offsetting the vibration energy when the fruits fall on the flexible harvesting net.

[0034] Compared with the prior art, the self-damping falling fruit harvesting platform of the present invention has the following advantages:

[0035] 1. Less damage to fruits: The fruits enter the flexible harvesting net by falling. The flexible harvesting net has passive flexibility, and the 4RRS rigid-flexible coupled parallel mechanism can identify the magnitude and direction of the fruit impact force, and then actively damp the vibration through the control algorithm. The whole harvesting method combines active damping and passive damping, which can quickly absorb and disperse the impact force of the fruits in a short time, thus ensuring the minimization of the impact force when the fruits fall, and further avoiding fruit damage.

[0036] 2. Better safety performance: Different from traditional mechanical harvesting devices and manual harvesting methods, the harvesting method adopted in the present invention does not require personnel to participate, fundamentally eliminating the risk of fruits falling and injuring people, thus ensuring the safety of the harvesting process.

[0037] 3. Higher degree of automation: The movement and navigation are realized through the mobile chassis, and an electromechanical control system is combined with a rotary encoder, a current / voltage sensor, and a brushless DC motor, etc., so as to realize real-time negative feedback closed-loop regulation. This design enables the self-damping falling fruit harvesting platform of the present invention to automatically complete the harvesting of fruits, and the harvesting process is completely automated, thus greatly improving the harvesting efficiency.

[0038] 4. Better adaptability: The self-damping falling fruit harvesting platform of the present invention can not only adapt to fruits of different sizes, weights, and growth heights, but also adapt to fruits with complex shapes and contours, and has strong adaptability to the harvesting of different types of fruits. At the same time, the equipped mobile chassis can move flexibly in different terrains and has all-terrain passability, which makes the self-damping falling fruit harvesting platform of the present invention have good terrain adaptability and fruit harvesting adaptability. Description of the Drawings

[0039] Figure 1 This is the overall structure diagram of the self-damping falling fruit harvesting platform of the present invention.

[0040] Figure 2 This is a schematic diagram of the harvesting robotic arm and its driving unit.

[0041] Figure 3 This is a schematic diagram of the mobile chassis.

[0042] Figure 4 This is the flowchart of the control method of the self-damping falling fruit harvesting platform of the present invention.

[0043] Figure 5 This is the flowchart of the harvesting method of the self-damping falling fruit harvesting platform of the present invention.

[0044] Figure 6 This is the local rigidification equivalent effect diagram of the flexible harvesting net.

[0045] In the figure: 1 - mobile chassis; 2 - driving unit; 3 - harvesting robotic arm; 4 - flexible harvesting net; 5 - controller; A, B, C, D are the numbers of the harvesting robotic arm. Detailed Description of the Invention

[0046] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0047] Refer to Figures 1-6 , the self-damping falling fruit harvesting platform of the present invention includes a mobile chassis and a 4RRS rigid-flexible coupling parallel mechanism arranged on the mobile chassis.

[0048] Refer to Figures 1-6 , the mobile chassis is connected to the 4RRS rigid-flexible coupling parallel mechanism and is used to drive the movement and navigation of the 4RRS rigid-flexible coupling parallel mechanism. This mobile chassis is a crawler chassis, which can be implemented with reference to the existing crawler mobile chassis on the market; in this embodiment, the mobile chassis includes a chassis shell, an all-terrain rubber crawler assembly, and a DC drive motor. Among them, the all-terrain rubber crawler assembly is installed outside the chassis shell, and the DC drive motor is installed inside the chassis shell; the all-terrain rubber crawler assembly moves under the drive of the DC drive motor;

[0049] Therefore, the mobile chassis in this embodiment distinguishes internal and external components with the chassis shell as the boundary; the chassis shell of the mobile chassis is made of steel, aluminum alloy, and carbon fiber materials to ensure appropriate structural strength and weight of the self-damping falling fruit harvesting platform of the present invention;

[0050] The outside of the mobile chassis is connected with rubber crawlers made of rubber and capable of 360-degree rotation in the horizontal direction. Compared with high manganese steel crawlers, such rubber crawlers can save more space. In addition, the rubber material has elasticity, which can play a certain vibration damping effect, has good grip, is not easy to slip, is more wear-resistant, and has good comfort performance, thus further assisting in the completion of independent vibration damping.

[0051] A DC drive motor with a DC drive motor cover made of stainless steel is fixedly installed inside the mobile chassis; the all-terrain rubber crawler assembly is connected to the DC drive motor to realize the electric drive movement function of the drop-type fruit harvesting platform with independent vibration damping of the present invention.

[0052] See Figures 1-6 , the 4RRS rigid-flexible coupled parallel mechanism includes a net spreading robotic arm assembly and a flexible harvesting net. Among them, the net spreading robotic arm assembly is used to realize the precise movement and independent vibration damping function of the harvesting robotic arm; the flexible harvesting net is connected to the end of the net spreading robotic arm assembly and can absorb and disperse the impact force of fruit falling during the harvesting process.

[0053] See Figures 1-6 , the net spreading robotic arm assembly includes a harvesting robotic arm and a drive unit.

[0054] See Figures 1-6 , there are four groups of the harvesting robotic arms, and the end effectors of the four groups of harvesting robotic arms are respectively connected to the four diagonals of the flexible harvesting net; in this embodiment, each group of harvesting robotic arms is a two-degree-of-freedom rotating robotic arm; correspondingly, there are two groups of drive units in each group of harvesting robotic arms, and the two groups of drive units are respectively located on two joints of the two-degree-of-freedom rotating robotic arm and are used to drive the swinging of the two arm bodies in the two-degree-of-freedom rotating robotic arm.

[0055] See Figures 1-6 , the flexible harvesting net is a square flexible burlap net, which is edge-sealed and has connection parts at its four diagonals for connecting with the end effectors of the harvesting robotic arms.

[0056] In this embodiment, the flexible harvesting net is a flexible collection net made of high-strength and highly wear-resistant polyester fiber and nylon. It can withstand long-term use and frequent cleaning, ensuring its durability and stability; the soft nature of the material can be appropriately adjusted according to the size and shape of the fruit, thereby protecting the quality and value of the fruit; it is made of environmentally friendly materials, meeting the requirements of modern society for environmental protection; it is lightweight, making it convenient to carry and move.

[0057] See Figures 1-6, the driving unit includes a brushless DC motor, a rotary encoder, and a current / voltage sensor. Among them, the rotary encoder is coaxially connected to the output shaft of the brushless DC motor and is used to measure and feedback the position, speed, and acceleration of the brushless DC motor in real time; the current / voltage sensor is connected to the armature winding of the brushless DC motor and is used to monitor the motor torque of the brushless DC motor in real time.

[0058] The rotary encoder takes the angle of the harvesting robotic arm as the collected data, drives to change the working magnetic field of the brushless DC motor, and then drives the brushless DC motor to produce a non-linear damping effect; the harvesting robotic arm serves as an execution device, and the signals generated by the two pass through a negative feedback system and change according to the actions of the rotary encoder and the current / voltage sensor. Finally, the energy brought by the fruit impact force is converted into the heat energy generated by the brushless DC motor in the non-linear damping state and the mechanical energy of the flexible harvesting net, thereby realizing the lossless fruit harvesting with autonomous vibration reduction.

[0059] See Figures 1-6 , the brushless DC motor has a torque sensing and vibration reduction control algorithm based on FOC control. Among them, the FOC control algorithm can precisely control the magnitude and direction of the magnetic field, making the motion torque of the motor stable, with low noise, high efficiency, and having a high-speed dynamic response.

[0060] See Figures 1-6 , the rotary encoder is a non-contact magnetic encoder, which has the advantages of high induction position accuracy, anti-vibration, anti-shock, high protection level, and long service life, and has a wider magnetic field intensity induction range.

[0061] See Figures 1-6 , the current / voltage sensor samples through a precision resistor and is converted into a voltage through I / V, and then the voltage signal is sent to the controller through the A / DC module after being processed by the driving unit, serving as the input parameter of the fruit impact force identification mathematical model, and is used to calculate the magnitude and orientation of the fruit impact force.

[0062] See Figures 1-6, the impact force of the fruit falling is transmitted to the output shaft of the brushless DC motor through the flexible harvesting net and the harvesting robotic arm, causing a change in the magnetic field of the armature winding of the brushless DC motor, thereby resulting in a change in current / voltage; due to the different magnitudes, directions of the fruit impact force and the pose of the flexible harvesting net, the current / voltage changes in the armature windings of the brushless DC motors on the joints of each group of harvesting robotic arms are also different. Therefore, by using the current output torque equation of the armature winding of the brushless DC motor, combined with the mechanical transmission characteristics of the flexible harvesting net and the 4RRS rigid-flexible coupled parallel mechanism, a mathematical model for identifying the fruit impact force is established, which can identify the magnitude and direction of the fruit impact force without additional sensors for subsequent precise autonomous vibration reduction control.

[0063] See Figures 1-6 , the control method of the autonomous vibration reduction falling fruit harvesting platform of the present invention includes the following steps:

[0064] Step S1: The mobile chassis transports the 4RRS rigid-flexible coupled parallel mechanism to the lower part of the plant where the fruit needs to be harvested; the DC drive motor of the mobile chassis is locked to achieve overall fixation, and the harvesting robotic arm on the 4RRS rigid-flexible coupled parallel mechanism is driven by a brushless DC motor to adjust the harvesting robotic arm to the initial state, thereby adjusting the pose of the flexible harvesting net to the preparatory form before harvesting, preparing for vibration reduction during fruit falling harvesting;

[0065] Step S2: When the fruit falls into the flexible harvesting net in a falling manner, the flexible harvesting net transmits the impact force of the fruit falling to the harvesting robotic arm, causing the joints of the harvesting robotic arm to swing; at this time, the joint torque changes of the four harvesting robotic arms are also different, causing the current / voltage generated by the armature winding of the brushless DC motor to change, and the change values of the current / voltage are collected through the current / voltage sensor;

[0066] Step S3: Construct a mathematical model for identifying the fruit impact force, and input the change values of the current / voltage collected by the current / voltage sensor into the constructed mathematical model for identifying the fruit impact force. The mathematical model for identifying the fruit impact force analyzes these change values of the current / voltage, and can identify the magnitude and direction of the fruit impact force without additional sensors;

[0067] Step S4: The controller formulates a corresponding vibration reduction harvesting strategy based on the magnitude and direction of the fruit impact force, generates a control command according to the formulated vibration reduction harvesting strategy, and thereby controls the movement trajectories of each group of harvesting robotic arms through the drive unit, driving the flexible harvesting net to move, so as to reduce or offset the vibration impact of the fruit falling on the flexible harvesting net, thereby achieving non-destructive harvesting of falling fruits;

[0068] Step S5: After the shock-absorbing harvesting of the fruits is completed, the driving unit controls the coordinated movement of each group of harvesting robotic arms to prompt the flexible harvesting net to pour the harvested fruits into the harvesting box;

[0069] Step S6: The driving unit controls the movement of each group of harvesting robotic arms to return to the initial state, and then repeats Step S2 - Step S5 to start the next round of fruit harvesting work.

[0070] See Figures 1-6 , the principle and construction method of the fruit impact force identification mathematical model include the following steps:

[0071] When the fruit falls, the flexible harvesting net deforms after being impacted by the falling fruit. At the moment of deformation, the flexible harvesting net will be locally stiffened, thus equivalent to four groups of harvesting robotic arms using ropes to hold the falling fruit at the four corners respectively; at the same time, due to the deformation of the flexible harvesting net, the impact force of the fruit fall is transmitted to the harvesting robotic arms and their driving units, which causes changes in the torques of the upper and lower joints of the harvesting robotic arms. When the fruit falls at different positions on the flexible harvesting net, the loads borne by each group of harvesting robotic arms are different. Therefore, the torques of the upper and lower joints of each group of harvesting robotic arms also have different changes; among them, when the fruit falls at different positions on the flexible harvesting net, the changes in the joint torques of the four groups of harvesting robotic arms have their own characteristics, as shown in the following table:

[0072]

[0073] It can be seen from the table that when the fruit falls at the exact middle position of the flexible harvesting net, the magnitudes and change trends of the joint torques of the four harvesting robotic arms are basically the same; when the fruit falls in the first quadrant area, second quadrant area, third quadrant area, and fourth quadrant area of the flexible harvesting net, the joint torque of the group of harvesting robotic arms closest to the fruit falling position among the four groups of harvesting robotic arms is the largest and the change response is the fastest; successively, the magnitudes and change trends of the joint torques of the two groups of harvesting robotic arms closer to the fruit falling position among the four groups of harvesting robotic arms are basically the same; while the change response of the joint torques of the two groups of harvesting robotic arms farthest from the fruit falling position among the four groups of harvesting robotic arms is the slowest;

[0074] When the fruit falls on the x-axis or y-axis of the flexible harvesting net, the magnitudes and change trends of the joint torques of the two groups of harvesting robotic arms closer to the fruit falling position among the four groups of harvesting robotic arms are basically the same; and the magnitudes and change trends of the joint torques of the two groups of harvesting robotic arms farther from the fruit falling position among the four groups of harvesting robotic arms are also basically the same; however, the change speed of the joint torques of the two groups of harvesting robotic arms closer to the fruit falling position is relatively fast, and the torque changes received are also relatively large;

[0075] When the joint torque of the harvesting robotic arm changes, a current or voltage will be generated accordingly in the brushless DC motor at the joint of the harvesting robotic arm, and the changes in these currents or voltages are the same as the changes in the joint torque of the harvesting robotic arm. Therefore, the position where the fruit falls on the flexible harvesting net can be deduced inversely based on the changes in the current / voltage generated by the upper and lower joints of the harvesting robotic arm, thereby forming a mathematical model for identifying the fruit impact force.

[0076] Therefore, the process of the mathematical model for identifying the fruit impact force to identify the direction of the fruit impact force is as follows:

[0077] Step S301: Taking the center of the flexible harvesting net as the coordinate origin, divide it into a first quadrant area, a second quadrant area, a third quadrant area, and a fourth quadrant area; then number the four groups of harvesting robotic arms.

[0078] Step S302: Compare the change values of the current / voltage in each group of harvesting robotic arms collected by the current / voltage sensor in the drive unit, determine the harvesting robotic arm with the largest change value of the current / voltage, and determine the quadrant area where the fruit falls on the flexible harvesting net according to the number of this harvesting robotic arm.

[0079] In addition, the process of the mathematical model for identifying the fruit impact force to identify the magnitude of the fruit impact force is as follows:

[0080] During the process of the falling fruit contacting the flexible harvesting net, the flexible harvesting net uses elastic force to buffer the impact force of the falling fruit. When the speed of the falling fruit becomes zero, the impact force of the falling fruit is basically converted into the elastic force of the flexible harvesting net, and the elastic deformation force is transmitted to the end effectors of the four groups of harvesting robotic arms through the deformation of the flexible harvesting net. Further, the elastic deformation force will continue to be transmitted to the brushless DC motors in the upper and lower joints of the harvesting robotic arm, manifested as a change in the torque of the upper and lower joints in the harvesting robotic arm; according to this chain reaction, conversely, a mathematical model for identifying the fruit impact force can be obtained based on the above process; since there is a functional relationship between the current / voltage of the brushless DC motor and the motor torque, the current / voltage of the brushless DC motor can be measured first to obtain the torque received by the brushless DC motor, and then this torque is converted back to the force received by the end effector of the harvesting robotic arm, so as to obtain the magnitude of the force borne by the end effectors of the four groups of harvesting robotic arms. Combining with the force spectrum model of the flexible harvesting net, the magnitude of the fruit impact force can be obtained, and the position where it acts can also be obtained according to the magnitude distribution of the fruit impact force.

[0081] See Figures 1-6 The specified steps of the shock absorption harvesting strategy are as follows:

[0082] Step S401: Real-time record the current or voltage data that is the same as the change in the joint torque of the harvesting robotic arm.

[0083] Step S402: making corresponding waveforms according to the recorded current or voltage data to detect the frequency and amplitude of the current or voltage in real time, thereby obtaining the frequency and amplitude of vibrations to which the four groups of harvesting mechanical arms are subjected;

[0084] Step S403: The vibrations to which the four harvesting robot arms are subjected will affect the motor torque of the brushless DC motors in the upper joints and lower joints of each harvesting robot arm. The generated motor torque is used as a known condition, and the position θ and angular velocity of the upper joint and lower joint of each harvesting robot arm are calculated in real time by using inverse kinematics. and angular acceleration Combined with the inverse dynamics equation of the second Lagrange equation, the optimal reverse torque that the upper and lower joints of each group of harvesting manipulators need to generate to offset the influence of the motor torque is calculated in real time. At the same time, a control instruction corresponding to the optimal reverse action torque is generated and sent to each group of driving units of each group of harvesting robot arms, so as to prompt the brushless DC motors at the upper joints and lower joints of each group of harvesting robot arms to output the calculated optimal reverse action torque, thereby driving the flexible harvesting net to move, so as to reduce or offset the vibration energy of the fruit falling on the flexible harvesting net.

[0085] See also Figures 1-6 The control method of the autonomous vibration-damping falling fruit harvesting platform of the present invention utilizes a 4RRS rigid-flexible coupling parallel mechanism, in conjunction with fruit impact force identification and an autonomous vibration-damping control algorithm, so that the falling fruits can be harvested stably, quickly, and non-destructively, thereby improving the harvesting success rate and lossless rate, reducing labor intensity and cost, and can be used for the lossless and automated harvesting of high-growing and high-quality fruits such as oil tea fruit, coconut, durian, and jackfruit.

[0086] The above is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited to the above content. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A free-falling fruit harvesting platform with autonomous vibration damping, characterized in that, It includes a mobile chassis and a 4RRS rigid-flexible coupled parallel mechanism arranged on the mobile chassis. Among them, the 4RRS rigid-flexible coupled parallel mechanism includes a net-spreading robotic arm assembly and a flexible harvesting net; the net-spreading robotic arm assembly includes multiple groups of harvesting robotic arms and multiple groups of driving units; the end effector of each group of harvesting robotic arms is connected to the flexible collection net; each group of driving units includes a brushless DC motor and a driving board for controlling the brushless DC motor. Among them, a rotary encoder and a current / voltage sensor are arranged on the driving board; the current / voltage sensor is connected to the armature winding of the brushless DC motor, and the motor torque of the brushless DC motor is calculated in real time by measuring the current / voltage and using the functional relationship between the current / voltage and the torque; the rotary encoder is coaxially connected to the output shaft of the brushless DC motor, and is used to detect in real time the rotation angle of the brushless DC motor and the speed and acceleration of the rotation of the brushless DC motor.

2. The self-damping falling fruit harvesting platform according to claim 1, wherein There are four groups of harvesting robotic arms, and the end effectors of the four groups of harvesting robotic arms are respectively connected to the four diagonals of the flexible harvesting net.

3. The self-damping falling fruit harvesting platform according to claim 1, wherein Each group of harvesting robotic arms is a two-degree-of-freedom rotary robotic arm; the two-degree-of-freedom rotary robotic arm includes a base, a lower swing arm, an upper swing arm, and an end effector arranged at the end of the upper swing arm. Among them, a lower joint is arranged between the base and the lower swing arm; an upper joint is arranged between the lower swing arm and the upper swing arm; correspondingly, each group of harvesting robotic arms has two groups of driving units, and the two groups of driving units are respectively located at the upper joint and the lower joint in the two-degree-of-freedom rotary robotic arm, and are used to drive the upper swing arm and the lower swing arm in the two-degree-of-freedom rotary robotic arm to swing.

4. The self-damping falling fruit harvesting platform according to claim 1, characterized in that, The flexible harvesting net uses a square flexible burlap net, and the edge of the flexible harvesting net is processed; connection parts connected to the end effectors of the harvesting robotic arms are arranged at the four diagonals of the flexible harvesting net.

5. The self-damping falling fruit harvesting platform according to claim 1, characterized in that, The mobile chassis is a crawler-type mobile chassis.

6. A control method for an autonomous vibration-damping falling fruit harvesting platform according to any one of claims 1-5, characterized in that, It includes the following steps: Step S1: The mobile chassis transports the 4RRS rigid-flexible coupled parallel mechanism to the lower part of the plant where the fruits need to be harvested; Subsequently, each group of driving units is used to control the actions of each group of harvesting robotic arms to adjust the harvesting robotic arm to the initial state, so as to adjust the posture of the flexible harvesting net to the preparatory form before harvesting; Step S2: When the fruits fall into the flexible harvesting net in a falling manner, the flexible harvesting net transmits the impact force of the falling fruits to the harvesting robotic arms, so as to cause the joints of the harvesting robotic arms to swing, thereby causing a current / voltage change in the armature winding of the brushless DC motor in the driving unit, and the change value of the current / voltage is collected by the current / voltage sensor; Step S3: A mathematical model for identifying the fruit impact force is constructed, and the change value of the current / voltage collected by the current / voltage sensor is input into the constructed mathematical model for identifying the fruit impact force, and the magnitude and direction of the fruit impact force are obtained through the mathematical model for identifying the fruit impact force. Step S4: The control unit formulates a corresponding vibration reduction harvesting strategy based on the magnitude and orientation of the fruit impact force. According to the formulated vibration reduction harvesting strategy, corresponding control instructions are generated, and based on this, the driving unit is used to control the movement trajectories of each group of harvesting robotic arms to drive the movement of the flexible harvesting net; Step S5: When the vibration reduction harvesting of the fruit is completed, each group of driving units controls the coordinated movement of each group of harvesting robotic arms to prompt the flexible harvesting net to pour the harvested fruit into the harvesting box; Step S6: Each group of driving units controls the movement of each group of harvesting robotic arms to return to the initial state, and then repeats Step S2 - Step S5 to start the next round of fruit harvesting work.

7. The control method of the free-falling fruit harvesting platform with independent vibration reduction according to claim 6, characterized in that, In Step S1, there are four groups of harvesting robotic arms. The end effectors of the four groups of harvesting robotic arms are connected to the four diagonals of the flexible harvesting net; each group of harvesting robotic arms is a two-degree-of-freedom rotating robotic arm; the two-degree-of-freedom rotating robotic arm includes a base, a lower swing arm, an upper swing arm, and an end effector provided at the end of the upper swing arm. Among them, a lower joint is provided between the base and the lower swing arm; an upper joint is provided between the lower swing arm and the upper swing arm.

8. The control method of the self-damping falling fruit harvesting platform according to claim 7, characterized in that, In Step S3, the steps of identifying the orientation of the fruit impact force through the fruit impact force identification mathematical model are: Step S301: Taking the center of the flexible harvesting net as the coordinate origin, it is divided into a first quadrant area, a second quadrant area, a third quadrant area, and a fourth quadrant area; then the four groups of harvesting robotic arms are numbered; Step S302: Compare the change values of the current / voltage of the brushless DC motors in the harvesting robotic arms collected by the current / voltage sensors in each group of driving units to determine the harvesting robotic arm with the largest change value of the current / voltage, and determine the quadrant area where the fruit falls on the flexible harvesting net according to the number of this harvesting robotic arm.

9. The control method of the self-damping falling fruit harvesting platform according to claim 8, characterized in that, In Step S3, the process of the fruit impact force identification mathematical model identifying the magnitude of the fruit impact force is: Step 311: During the process of the fruit impacting the flexible harvesting net, the current / voltage data of the brushless DC motors in the upper and lower joints of the four groups of harvesting robotic arms are recorded in real time; Step 312: Find the moment when the current / voltage of the brushless DC motors in the upper and lower joints of each group of harvesting robotic arms first reaches the extreme value in the recorded current / voltage data, obtain the value of the current / voltage at this moment, and convert it into the corresponding motor torque according to the functional relationship between the current / voltage and the torque; Step 313: Obtain the rotation angles of the brushless DC motors in the upper and lower joints of the harvesting robotic arm through the rotary encoder, thereby obtaining the posture of the harvesting robotic arm, and combining the motor torque obtained in Step 312, calculate the force borne by the end effector of each group of harvesting robotic arms. By performing vector summation on the forces borne by the end effectors of each group of harvesting robotic arms, the magnitude of the fruit impact force is obtained.

10. The control method of the self-damping falling fruit harvesting platform according to claim 9, characterized in that, In Step S4, the steps of specifying the vibration reduction harvesting strategy are: Step S401: Record the current or voltage data that is the same as the change in the joint torque of the harvesting robotic arm in real time; Step S402: Make corresponding waveforms based on the recorded current or voltage data to detect the frequency and amplitude of the current or voltage in real time, so as to obtain the frequency and amplitude of the vibration received by the four groups of harvesting robotic arms; Step S403: The vibration received by the four groups of harvesting robotic arms will have an impact on the motor torque of the DC brushless motors in the upper joints and lower joints of each group of harvesting robotic arms; taking the generated motor torque impact as a known condition, use inverse kinematics to calculate in real time the positions, angular velocities and angular accelerations of the upper joints and lower joints in each group of harvesting robotic arms, and combine with the inverse dynamics equation of Lagrange's second kind to calculate in real time the optimal reverse reaction torque that the upper joints and lower joints in each group of harvesting robotic arms need to generate to offset the received motor torque impact. At the same time, generate a control command corresponding to the optimal reverse reaction torque and send the control command to each drive unit of each group of harvesting robotic arms, so as to prompt the brushless DC motors at the upper joints and lower joints of each group of harvesting robotic arms to output the calculated optimal reverse reaction torque, thereby driving the flexible harvesting net to move to reduce or offset the vibration energy when the fruits fall on the flexible harvesting net.

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