2.1 Modular architecture design and analysis
Due to various problems existing in the cage, In view of modularization, design a modular marine ranching UUV system, According to the modular structural system, divided into main body, net clothes cleaning, net clothes repair, dead fish recycle module and underwater station. According to the idea of hardware modularization, divided into power, control, frame, propeller, camera, lighting, floating , manipulator and working module. The main body is a remote operated vehicle(ROV) with cable from the workstation, which can be used separately for cage monitor to check the growth and living environment of fish. The modular UUV system of ocean ranching is shown in figure 4.
Main body is given path plan by workstation first, equipped with camera module for cage monitor. When found the cage sediment attached to a certain degree in the cage,dead fish or the damaged net clothes, main body sent information to the workstation, then through signal transmission, connect the required main body with the working module, control the working module to accomplish different tasks by wireless signals transmission.
The working module system is divided into three independent unit modules, each module has a standardized and universal connection interface and the control processor involved can work together. According to the different application environment and task, corresponding working module is combined with body to meet different requirements. Modular design facilitates improve performance, function expansion and convenient maintenance[13-14].
2.2 Modular Main Robot
In this paper, the main body include the visual system, the motion system, the battery and control system, the frame,and floating body and the docking device, as shown in figure 5. The motion system equipped with four horizontal thrusters, four vertical thrusters. The battery and control system include a control bay and two battery bay. The visual system include a camera located at the head of the control bin, a PTZ camera located at the top plate of the main body and two LED. The main body will be equipped more modules according to different work tasks, such as sonar to percept fish swarm and damage location of net clothes, wireless communication system to transmission information and etc. The main body head is streamlined to reduce the motion resistance. The propeller system is installed on the wing plate.
(1) Visual system
The visual system includes the control cabin of built-in camera, the two LED lamps and the integrated cloud head system, which is used for close and long-distance observation and analysis respectively. It can better adjust the working condition in real time to complete the fish state analysis and the cage monitor.
(2) Motion system
It includes four horizontal thrusters and four vertical thrusters. Through control in different ways, which can change the position and motion form of the vehicle.
The main body needs to carry different working modules according to different working conditions, so the balance of the main body is necessary. The following two schemes are described:
(1)Supply with weight blocks or buoyancy materials;
(2)Barycenter regulator and floating center regulator, as shown in figure 6.
2.3 Net clothes cleaning working module
If remove attachments on the net clothes, the net cage can increase the oxygen content, improve the fluidity of the water, increase the growth rate of the fish and reduce the frequency of the fish deaths. At present, the main working methods of underwater cleaning vehicle are brush, high pressure water jet, ultrasonic wave and so on[15-16].
The net clothes cleaning module is connected to the main body which carries the power system. The control signal is transmitted, analyzed and processed by the main body control system. The brush is driven by the motor to clear the attachment on the net cage.
Scheme one: The net clothes cleaning robot module adopts two roller brushes, which can not only clean the net clothes, but also drive the vehicle to walk on the net clothes. After working with Senkott Company to create a prototype, as shown in figure 7. It is found that the cleaning and driving effect is not ideal, and the secondary deposition rate of the net clothes is fast after cleaning and difficult to observe during the cleaning process.
Scheme two: Because the front and rear rollers are easy to destroy, so adopt the crawler and propeller to drive and add the cleaning brush at the bottom, which is driven by the motor installed at the tail of the vehicle. The front and rear rollers are only used for cleaning, as shown in figure 8.
In this paper, design a new cleaning brush with lateral hard hair and bottom soft hair. When cleaning the net clothes, the brush sinks into the net clothes and the length of soft hair is lower than the bottom of the crawler, so that soft hair can have enough allowance through the net clothes and can reduce the brush damage to the net clothes. The cleaning brush completes the large area cleaning work through the lateral hard hair, its bottom soft hair can carry on the deep cleaning attachment to the net clothing. The new brush and drive way are shown in figure 9.
In view of the problems in the test of the first generation prototype, using the second solution, the second generation of net clothing cleaning underwater vehicle model was built in collaboration with Senkott Company. Through experiments, it is found that under the dual function of the main cleaning brush and the auxiliary cleaning roller, the crawler is used to replace the roller to walk on the net, cleaning and walking effects are greatly increased. The model and material object after docking with the main body are shown in figure 10.
2.4 Net clothes repair working module
Under the action of natural such as wind and wave flow and biological factors, cage netting is easy to be damaged, resulting in property loss.For the traditional fishery aquaculture, the fishing net is pulled to shore by the staff to repair, which is time-consuming and inefficient.Therefore, need to design an UUC that can repair the net clothing automatically under water.
In this paper, the net clothes repair working module is composed of two sets of manipulator devices, which are divided into repair manipulator and wire cutting manipulator. The two manipulators cooperate with each other to complete the repair of net clothes[17]. As shown in Figure 11, pull the wire from the upper manipulator out and clench it, and then cut it by the lower manipulator.
1) Repair manipulator:
As shown in figure 11’s upper manipulator, it is a multi-degree-of-freedom manipulator. The front end of the manipulator claw is responsible for the knot of the net clothes. Among them, knotting is to use a kind of binding device similar to stapler to tie and fix the net clothes.
2) Wire cutting manipulator:
As shown in figure 11’s lower manipulator, it is mainly responsible for wire cutting. The manipulator has five degrees of freedom, The wire cutting process can be completed by using these five degrees of freedom to coordinate with each other.
In the repaire process, one of the most important problems is the clamping problem of the wire head, because the repair manipulator claw must be separated and closed in performing the clamping action. It is especially difficult for the underwater environment. The wire cutting work is handed over to the wire cutting manipulator, so that repair manipulator claw can be free, which can solve this problem to a certain extent. The repair manipulator need to complete two opening and closing actions in a very small space, because the size of the net mesh is about 30 mm, so the size of the mechanical claw should below 20 mm. The size of the internal actuator is limited to 12 mm *12mm. Adopt the micro hydraulic cylinder to complete the above action.
The net clothes repair working module needs to complete the following actions, claw open——repair claw out——claw closed——complete the line fetching action——claw open——claw back——claw closed——hold the wire tight——wire cutting. Through this cycle complete the repair net clothes. Therefore, it is necessary to have a steering gear to control the closing and opening of the claw, a stepping motor to control the rotation of the wrist and a stepping motor to control the lead screw to carry out forward and retreat of the manipulator. As shown in figure 12.
If a metal bar material is to be cut off, its shear strength can be inquired by the corresponding material and is a fixed value M. The cross-sectional area of the material is S and the shear force required to cut the rod material is F=M*S. The shear force required is as long as the force of this F is reached on the shear plane, it can be cut. This only reflects the size of the force, it has nothing to do with the sharpness degree of the cutting manipulator.
The design parameters of the net clothes repair working module are as follows:
1. Wire cutting head parameters:
The material is No.45 normalizing steel, the wire cutting head size is l=a*b; a=16 mm, b=[0.35,0.42] mm;
2. Working conditions of cylinder:
Inner diameter 5 mm, set the pressure as 4MPa, then the pressure is 78.5N.
3. Wire clamp head parameters:
The material is No.45 normalizing steel, knurling process.
In the repaire process, in the upper claw of the repair manipulator will have a nylon rope through the hole, the wire head is clamped by the claw shear block and the fixed block, then fixed in the front end of the repair manipulator. At this time, the claw is open, the lead screw slide rail system feed, and the repair manipulator is sent into the complete net mesh around the broken net mesh, as shown in figure 13, the squares in the figure are section diagrams of the repaired claws.
After entering the net mesh, the claw is closed, the wire head is loosened by the claw internal cutting wire block and the internal claw clamp wire block is clamped to complete the wire head exchange. Then the claw is opened in the same way and push the repair manipulator out of the damaged net mesh. A sewn nylon rope has been pulled out between the damaged net mesh. Then the repair claw is closed again, the repairing manipulator clamps the two nylon ropes that have been closed, and the repairing manipulator moves in the opposite direction and tighten the nylon rope. When it is tightened to the appropriate tightness, the fixing needle of the knot rope is fixed on the two nylon ropes by the repairing manipulator to complete the knot of the nylon rope, Then cut two nylon ropes at the back end of the knot by the wire cutting manipulator..
After the above work is completed, the repair manipulator internal fretting cylinder drives the claw shear block to cut the residual nylon rope wire head, and clamps the wire head again with the claw fixed block to open the next working cycle. After the docking of the net clothes repair working module and the main body, as shown in figure 14.
2.5 Dead fish recycling working module
In the process of marine ranching farming, the deposition of dead fish often occurs. If it can not be cleared in time, it will contaminate water, spread diseases, endanger the safety of deep-sea aquaculture and is not conducive to the growth of other fish. At present, cage dead fish mainly adopts manual recycle, which is difficult to operate, high labor intensity and low working efficiency.
The fish will sink to the bottom of the net cage just after death and will not float on the sea until it rots, so it must be recyced before the dead fish rots. After the dead fish sink at the bottom of the cage, due to the action of the current, it will gradually gather in the corner of the net cage. Therefore, it is urgent to develop an UUV for the recycle of dead fish in net cages.In this paper, The dead fish recycle working module is docked with the main body to recycle dead fish, as shown in figure 15.
Because the dead fish pile up and gather in the corner of the bottom of the cage, the most favorable way of recycle is that the dead fish working module climbs on the bottom of the cage through the wheel or crawler. Relying on the friction with the net clothes, can achieve more stable run and higher recycle efficiency.
Based on the principle of broom and roller, the structure of slope plate (roller) and wheel (broom) is designed. The slope plate is a group of rolling bars with power, each rolling rod is covered with blunt thorns, similar to the transmission belt, the idea comes from the deep-sea mining vehicle[18-19]. The dead fish can be swept into the recycle device with the slope plate. The main structure is a set of sweeping wheel group, sweeping the dead fish into the recovery bin.The dead fish recycle working module is shown in figure 16.
The dead fish recycle module includes the slope plate transmission system, the sweeping wheel group system and recycling delivery and storage system.
1. Slope plate transmission system:
Transport dead fish attached to the bottom of the net cage to the module temporary storage platform for easy recycle, mainly including slope plate, transmission rod, temporary storage platform and transmission system, as shown in figure 17. The sloping plate is a 35-degree circular slope that like a shovel to scoop up dead fish deposited in the net and send it up to the driving rod by thrust and frictional force; The transmission rod is made of nylon rod material with blunt spurs of rubber material on it to increase the friction force of the transmission. Eight transmission rods are distributed side by side to form a "track" to transport dead fish to the temporary storage platform; dead fish are cleaned periodically by the sweeping wheel group system after piling up on the temporary storage platform; the drive system is a gear drive, and the power is provided by the motor. The top drive rod is driven by the synchronous drive belt, and the idler gear transmits the power to make each drive rod move at the same speed and direction.
2. Sweep wheel group system:
It consists of 24 special sweeping wheels fixed to a drive shaft by screws, as shown in figure 18. The drive shaft is a metal aluminum shaft which can effectively guarantee the strength. The power is provided by a waterproof motor through a bevel gear reducer. By controlling the rotation of the sweeping wheel group, the dead fish collected from the slope plate transmission rod system is swept to the storage bin to realize the recycle of dead fish.
3. Recycle delivery and storage system:
It includes storage bin, transmission rods and transmission systems. as shown in Figure 19. The sweeping wheel group system sweeps dead fish into the storage bin. Due to gravity, dead fish will pile up on the edge of the transmission rods, so it is necessary for the transmission system to transport the dead fish to the deep in storage bin and maximize the use of storage space. The principle of transmission rod and transmission system is the same as that of slope plate transmission system.
The dead fish recycle working module docked with the main body to form dead fish recycle module vehicle in marine ranching, as shown in figure 20.