Four-finger flexible gripper applied to four-rotor unmanned aerial vehicle

Abstract

The invention belongs to the technical field of mechatronics, and relates to a four-finger flexible gripper applied to a four-rotor unmanned aerial vehicle. The device is characterized by comprising an electric control part, a soft claw base, a fishing line, fingers and a connecting piece between the electric control part and the base, the electric control part comprises two speed reduction direct current motors, a winch, an electric control assembly, a lithium battery and an upper computer. And four fingers are fixed at four corners below the soft claw base. The base is fixedly connected with the fingers, and the fingers are fixedly connected through screws. Motor racks are fixed to the middle positions of the fingers on the same side above the base, and all the motor racks are connected through screws. Logarithmic spiral lines are benchmarked on the elephant nose and serve as driving lines to be benchmarked on tendons; meanwhile, the state when the tendons are relaxed is used as the initial state of the soft claws, and the effects that the soft claws are folded when the tendons are tensioned and unfolded when the tendons are relaxed are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechatronics, and relates to a four-finger flexible gripper applied to a quadrotor UAV, which adopts a single tendon drive and a logarithmic spiral structure. Background Art

[0002] In recent years, the iteration of mechanical gripper technology has gradually accelerated, and important practical values have been demonstrated in many fields. With the development of the intelligent grasping technology of quadrotor UAVs carrying mechanical grippers, higher challenges are posed to the operation of mechanical grippers in dynamic scenarios, and mechanical grippers need to have more stable and rapid strain capabilities.

[0003] Currently, mechanical grippers can be divided into flexible mechanical grippers and rigid mechanical grippers according to the rigidity of materials. Rigid mechanical grippers are composed of rigid materials such as metals and hard plastics, and the joints usually adopt driving methods such as motors, gears, and linkages. The motion mode is based on precise mechanical structures, and the control relies on high-precision sensors. They are suitable for high-load and high-precision tasks, but have low flexibility and are difficult to adapt to irregular objects. Flexible mechanical grippers are composed of flexible materials such as silica gel and soft plastics, without rigid joints, and rely on deformation to achieve grasping. They have the ability of adaptive grasping, can adapt to different shapes and vulnerable objects, and the control methods include pneumatic drive, hydraulic drive, and wire-pulling drive. When using a rigid mechanical gripper to grasp in the grasping task of a quadrotor UAV carrying a mechanical gripper, the contact force generated on the mechanical gripper is relatively large, which easily causes a large change in the attitude of the UAV, thus causing the UAV to be unstable.

[0004] To solve the relatively large contact force generated by applying a rigid mechanical gripper to a quadrotor UAV, using a flexible mechanical gripper has great advantages. However, traditional flexible grippers use pneumatic or hydraulic control methods. Due to the large mass and volume of the driving mechanism, and the limited carrying mass and space on a quadrotor UAV, this control method does not have advantages. For traditional flexible grippers using wire-pulling drive methods, due to structural problems, the grasping force is relatively small, and it is difficult to grasp items with relatively large masses. Summary of the Invention

[0005] To solve the above problems, by combining the elephant nose structure and wire-pulling drive, a four-finger flexible gripper applied to a quadrotor UAV is provided, which is a four-finger flexible gripper with a single tendon drive and a logarithmic spiral structure for UAV grasping.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A four-finger flexible gripper applied to a quadrotor drone, which includes an electric control part, a gripper base, tendons, fingers, a motor frame, and a winch; the electric control part includes two reduction DC motors, a lithium battery, a motor driver, a single-chip microcomputer, a host computer, and a communication module.

[0008] Four exactly the same fingers are fixed at the four corners below the gripper base, and two fingers are installed in parallel on each side of the base.

[0009] The base and the fingers are connected by screws, and the motor frame is connected by screws at the middle position above the base. In order to precisely control the scaling of the fingers by the rotation of the winch, each finger uses two threading holes to limit the stretching of the tendon.

[0010] The fingers of the gripper are composed of phalanges, and each finger is controlled by a tendon.

[0011] The phalanges are realized in the following way:

[0012] When the fingers are fully closed, that is, the gap between the phalanges is the smallest, the inner shape of the fingers is a logarithmic spiral, and its structural shape is shown in Equation (1):

[0013]

[0014] Among them, t is the parameter of the equation, x(t) and y(t) are the coordinates of the logarithmic spiral under the corresponding parameters respectively, a is the initial radius of the logarithmic spiral, and b is the growth rate of the logarithmic spiral.

[0015] When the fingers are fully relaxed, that is, the gap between the phalanges is the largest, the outer shape of the fingers is a central logarithmic spiral, and the central logarithmic spiral is defined as the midpoint trajectory of adjacent two turns of the spiral, and its structural shape is shown in Equation (2):

[0016]

[0017] Among them, x c (t), y c (t) are the coordinates of the central logarithmic spiral under the corresponding parameters respectively.

[0018] When the fingers are straightened, that is, the outer side of the fingers is in a straight state, b determines the included angle φ on both sides, as shown in Equation (3):

[0019]

[0020] The present invention adopts a structure with seven phalanges. When the finger is straightened, the angle between the spiral line and the central spiral line is approximately 15°, and the initial radius of the logarithmic spiral line is 5 mm. The values of parameters a and b are determined based on these characteristics, and then the logarithmic spiral line and the central logarithmic spiral line are drawn. Twelve rays with the origin as the endpoint and spaced 30° apart are used, and one of them must pass through the starting point of the logarithmic spiral line and the central logarithmic spiral line, that is, the coordinate point when t = 0. These rays serve as the dividing lines for designing the phalanges. There are four intersection points between every two adjacent dividing lines and the logarithmic spiral line and the central logarithmic spiral line. A planar quadrilateral contour of a phalanx is formed by these four intersection points. The planar quadrilateral contours of each phalanx are combined along the central logarithmic spiral line to obtain the planar contour of the finger, and a finger is obtained through 3D printing after boss stretching and tendon threading holes are drilled.

[0021] For the tendon mentioned above, nylon fishing line is used. The surface of this line is smooth, and it has relatively small friction with the threading holes on the finger and the threading holes on the chassis when conducting tensile force, and it has high strength and can bear a relatively high load. When the motor drives the winch to rotate, the tendon will make corresponding movements, so that the gap between the phalanges becomes larger or smaller, which is conducive to the finger to spread or close.

[0022] For the winch mentioned above, its central hole can be in interference fit with the output shaft of the DC reduction motor, and 10 openings are left on both sides of the winch to facilitate the fixation of the tendon on the winch.

[0023] A further feature is that parameters a and b are selected according to the characteristics of the finger, and the logarithmic spiral line and the central logarithmic spiral line are drawn, where a = 5 and b = 0.22.

[0024] A further feature is that the base and the winch are made by 3D printing with PLA material.

[0025] A further feature is that the finger is made by 3D printing with TPU 95A material.

[0026] A further feature is that in order to facilitate the operation of the gripper on the unmanned aerial vehicle, ROS (Robot Operating System) is used as the upper computer, and the single-chip microcomputer is used as the lower computer, which is responsible for controlling the motor. Data is sent to the lower computer through the keyboard keys of the upper computer, and communication between the upper computer and the lower computer is carried out using a communication module. After the lower computer receives the signal sent by the upper computer, it sends a control signal to the motor driver, and the motor driver controls the rotation of the DC motor, and the lithium battery supplies power to the motor driver.

[0027] A further feature is that the single-chip microcomputer adopts STM32f103c8t6;

[0028] A further feature is that the communication module adopts a USB to TTL converter;

[0029] A further feature is that the motor driver adopts TB6612FNG;

[0030] Further features: The battery uses a 3S lithium battery;

[0031] The four-finger flexible gripper of the present invention for use in drone grasping is controlled by one tendon for each finger. When the tendon is completely relaxed, the gripper opens, and when the tendon is tightened, the gripper closes. The finger design adopts a logarithmic spiral structure, similar to an elephant's trunk, with a wrapping grasping effect. While reducing the number of tendons, it significantly improves the grasping ability. Description of the Drawings

[0032] Figure 1 It shows the inner and outer structures of the finger of the present invention.

[0033] Figure 2 The finger is composed of phalanx units.

[0034] Figure 3 The finger is 3D printed.

[0035] Figure 4 It is the overall assembly drawing.

[0036] In the figure: 1 logarithmic spiral, 2 central logarithmic spiral, 3 planar quadrilateral contour of the phalanx, 4 planar contour of the finger, 5 central logarithmic spiral of the combined phalanx, 6 connection part between the finger and the gripper base, 7 stud reserved hole, 8 phalanx, 9 finger threading hole, 10 finger, 11 gripper base, 12 base threading hole, 13 winch, 14 motor frame, 15 DC geared motor. Detailed Embodiment

[0037] The following combines the technical solutions and the drawings to detail the specific embodiments of the present invention.

[0038] The present invention provides a four-finger flexible gripper applied to a quadcopter drone, and the manufacturing process of its finger is as follows. When the finger is completely closed, its inner structure is a logarithmic spiral; when the finger is completely open, its outer structure is a central logarithmic spiral. Here, a 7-phalanx structure is used, the angle between the spiral and the central spiral is about 15°, and the initial radius of the logarithmic spiral is 5 mm. According to these features, the parameters a = 5 and b = 0.22 can be obtained, and the length of the finger is 712 mm. As Figure 1 shown, each phalanx is composed of a quadrilateral 3 formed by the intersection of the logarithmic spiral 1, the central logarithmic spiral 2, and the dividing line passing through the origin. Here, 3 is the 9th phalanx quadrilateral. As Figure 2 shown, select the first 7 phalanges, and arrange these 7 phalanges in sequence according to the central logarithmic spiral 5 to obtain the finger planar contour 4. The central logarithmic spiral is translated 2 mm outward to connect the phalanges, and 6 is the planar structure of the connection part between the finger and the gripper base.

[0039] Figure 2The shown planar figure is stretched, and the knuckles 8 are connected together through the outer connecting parts. The finger threading holes 9 are located at the center of each knuckle, 2 mm away from the inner side of the knuckle. At the connection between the finger and the base, a regular hexagonal hole 7 with an inscribed circle diameter of 2.9 mm is dug, and the hole can be in interference fit with a regular hexagonal stud of M2×15 so that the finger and the base can be connected by screws. The printing material of the finger is TPU 95A, and the obtained finger is as Figure 3 shown.

[0040] Figure 4 For the assembly drawing of the gripper, the finger 10 is connected to the gripper base 11 by screws. The model of the DC reduction motor 15 is GA25-370, the reduction ratio is 500, and the drive voltage is 12V. The motor is installed on the motor frame 14 by screws, and the motor bracket and the gripper base are connected by screws. The material of the base is PLA and is made by 3D printing. The tendon connecting the gripper and the winch 13 uses a 15-pound fishing line. One end of the line is fixed on the winch, and the other end passes through the base wire hole 12, then passes through 7 wire holes on the finger and is fixed at the end of the finger. Each motor controls two fingers on the same side, and the tendon remains taut when the finger is completely relaxed.

[0041] In terms of electronic control, the upper computer uses ROS and adopts the method of topic communication. The publishing end uses the keyboard library in python. When the W key on the keyboard is pressed, a message of the motor rotating forward is published; when the S key on the keyboard is pressed, a message of the motor rotating backward is published. The subscribing end uses the serial library in python. When the published message is subscribed, corresponding processing is performed according to different messages. For example, when the message of the motor rotating forward is subscribed, the message of the motor rotating forward is published to the serial port through the serial port in the callback function and waits for the processing of the lower computer.

[0042] The lower computer uses STM32f103c8t6. After receiving the corresponding data through the serial port, it generates a PWM signal for the DC motor drive module TB6612FNG, so that the motor generates corresponding actions, and then completes the operations of grasping and releasing.

Claims

1. A four-finger flexible gripper applied to a quadrotor drone, characterized in that It includes an electronic control part, a gripper base, tendons, fingers, a motor frame, and a winch; the electronic control part includes two DC geared motors, a lithium battery, a motor driver, a single-chip microcomputer, a host computer, and a communication module; Four identical fingers are fixed at the four corners under the gripper base, and two are installed in parallel on each side; The base and the fingers are connected by screws, and the motor frame is connected by screws at the middle position of the fingers above the base; The fingers of the gripper are composed of one knuckle each, and each finger is controlled by one tendon; The gripper knuckle is implemented in the following way: When the fingers are fully closed, that is, the gap between the knuckles is the smallest, the inner shape of the finger is a logarithmic spiral, and its shape is shown in Equation (1): Among them, t is the parameter of the equation, x(t) and y(t) are the coordinates of the logarithmic spiral under the corresponding parameters, a is the initial radius of the logarithmic spiral, and b is the growth rate of the logarithmic spiral. When the fingers are fully relaxed, that is, the gap between the knuckles is the largest, the outer shape of the finger is a central logarithmic spiral, and the central logarithmic spiral is defined as the midpoint locus of two adjacent turns of the spiral, and its shape is shown in Equation (2): where x c (t) and y c (t) are the coordinates of the central logarithmic spiral under the corresponding parameters respectively; When the finger is straightened, that is, the outer side of the finger is in a straight state, b determines the included angle φ on both sides, as shown in Equation (3): According to the included angle of 15° on both sides when the finger is straightened and the initial radius of the logarithmic spiral is 5 mm, the values of parameters a and b are determined, so as to draw the logarithmic spiral and the central logarithmic spiral; use twelve rays with the origin as the end point and an interval of 30°, and one of them needs to pass through the starting point of the logarithmic spiral and the central logarithmic spiral, that is, the coordinate point when t = 0; these rays are used as the dividing lines for designing the knuckles, and there are four intersection points between every two adjacent dividing lines and the logarithmic spiral and the central logarithmic spiral. A planar quadrilateral contour of a knuckle is formed by these four intersection points; the planar quadrilateral contours of each knuckle are combined along the central logarithmic spiral to obtain the planar contour of the finger, and a finger is obtained by 3D printing after boss stretching and tendon threading holes are dug.

2. The four-finger flexible gripper according to claim 1, wherein Each finger restricts the routing of the tendon with two threading holes on the gripper base.

3. The four-finger flexible gripper according to claim 1, characterized in that, The tendon mentioned above uses nylon fishing line.

4. The four-finger flexible gripper according to claim 1, characterized in that, For the winch mentioned above, its central hole can be interference-fitted with the output shaft of the DC geared motor, and 10 openings are left on both sides of the winch for fixing the tendon on the winch.

5. The four-finger flexible gripper according to claim 1, wherein The logarithmic spiral and the central logarithmic spiral are drawn according to the parameters a and b selected according to the characteristics of the finger, a = 5, b = 0.

22.

6. The four-finger flexible gripper according to claim 1, characterized in that, The base and the winch are made by 3D printing with PLA material.

7. The four-finger flexible gripper according to claim 1, wherein The finger is made by 3D printing with TPU 95A material.

8. The four-finger flexible gripper according to claim 1, wherein In order to facilitate the operation of the gripper on the unmanned aerial vehicle, ROS is used as the host computer and the single-chip microcomputer is used as the slave computer. Data is sent from the keyboard keys of the host computer to the slave computer, and communication between the host computer and the slave computer is carried out using the communication module. After the slave computer receives the signal sent by the host computer, it sends a control signal to the motor driver, and the motor driver controls the rotation of the DC motor, and the lithium battery supplies power to the motor driver.

9. The four-finger flexible gripper according to claim 1, characterized in that, The single-chip microcomputer uses STM32f103c8t6.

10. The four-finger flexible gripper according to claim 1, wherein The motor drive module uses TB6612FNG, and the lithium battery mentioned above is a 3S lithium battery.

Images