Design of an Intelligent Feeding System

The article elaborates on the design method of an intelligent feeding system . The feeding system is an important part of the automatic production line, which provides raw materials for other units of the automatic production line. It is controlled by PLC, which is described from many aspects, such as structure design, pneumatic circuit design, control circuit design and PLC program design. It analyzes the design idea and principle of intelligent feeding system in detail, and provides an effective reference for the design of automatic production line.


Introduction
In the whole industry 4.0 environment, it can bring the improvement of production efficiency, safety performance, very large and more powerful data analysis ability, as well as the flexibility of the whole production.Some advantages are recognized and accepted by more and more people, and the significance of automatic production line is becoming more and more prominent [1].
1.When the automatic production line is realized in an enterprise, all or part of the production process of products is completed by mechanical equipment, instruments and automatic devices, and human beings can be free from heavy labor.Human function can be in the system design, assembly, adjustment, inspection, supervision of the production process, quality control, and adjustment and maintenance of automation equipment and devices, without human direct participation in the operation.
2. The wide use of various robots in the production process has improved the automation, intelligence and industrialization of industrial production, and promoted the development of science and technology to a higher level.
3. The automatic production line not only improves the working conditions and reduces the labor intensity of workers, but also ensures the production safety, improves the labor productivity and product quality, reduces the loss of energy and raw materials, saves auxiliary processing time, and finally reduces the production cost.It creates greater value and profits for the enterprise.
The feeding system is an important part of the automatic production line, which provides raw materials for other units of the automatic production line.Its function is to automatically push out the workpiece (raw material) placed in the silo to the discharge table as required, so that the manipulator of the conveying unit can grab and convey it to other units [2].

Structural Design
The structure of the feeding system device mainly comprises a workpiece storage device and a workpiece push-out device.As shown in Figure 1.
(1) workpiece storage device The tubular silo, the material shortage detection assembly and the inductive proximity switch form a workpiece storage device.The tubular silo consists of a silo base fixed on the support frame and a transparent plastic tube silo.Workpieces are placed from the top of the plastic tube.When the workpieces need to be supplied, the PLC controls the action of the pushing cylinder behind the silo base to push out the bottom workpiece.
A photoelectric switch is installed at the bottom of the tubular silo and at the position of the 4th layer workpiece.Their function is to detect whether there are workpieces in the silo or whether the workpieces are sufficient.If there are only three workpieces in the silo, the photoelectric switch above acts, indicating that the workpieces are insufficient; If there are no workpieces in the silo, the photoelectric switch below operates.The signal status of these two photoelectric proximity switches can be used to reflect whether there are enough or no workpieces in the silo [3] .
The function of the inductive sensor mounted on the side of the silo base is to detect whether the lowest part in the silo is a metal part.(2) workpiece push-out device The workpiece pushing device comprises the push material cylinder, the top material cylinder and a corresponding electromagnetic valve group.The two cylinders are fixed on the cylinder support plate .The material pushing cylinder is arranged at the bottom layer of the material bin, and the piston rod of the material pushing cylinder can pass through the bottom layer of the material bin; when the piston rod is at the retreating position, the material pushing cylinder and a bottom layer workpiece are at the same horizontal position, and the material supporting cylinder and a sub-bottom layer workpiece are at the same horizontal position [4].As shown in Figure 2.
The function of the work piece push out device is to push out the work piece from the bottom of the silo onto the material table.The principle of operation of the unit is that when the workpiece is to be pushed out onto the material table, the piston rod of the top material cylinder is first pushed out to hold down the next lower workpiece; then the piston rod of the push material cylinder is pushed out to push the lowest workpiece onto the material table.After the pusher cylinder is back, the top cylinder returns and releases the lower workpiece.In this way the workpiece in the silo is automatically moved downwards by gravity, ready for the next push out of the workpiece.
The pushing cylinder pushes the workpiece out onto the discharge table.The surface of the discharge table is provided with a small hole, and a cylindrical photoelectric proximity switch is arranged below the discharge table, which emits light upward when working, so as to detect whether a workpiece exists through the small hole, so as to provide a signal for the system to determine whether there is a workpiece on the discharge table of the unit.
In addition to the above two main parts, the feeding unit device also has a series of other components, such as a support frame, a solenoid valve group, a wiring port, a trunking, and a bottom plate, to form a whole.

Connection and Commissioning of Gas Circuit
The pneumatic control circuit is shown in Figure 3. Air circuit connection steps: Starting from the manifold plate, connect the solenoid valve and cylinder with an air pipe with a diameter of 4mm as shown in Figure 3, and then connect the air source processor with the manifold plate air inlet with an air pipe with a diameter of 6mm [5].
Debugging of the gas circuit: 1) Use the manual reversing button on the solenoid valve to verify whether the action positions of the top material cylinder and push material cylinder.are correct.2) Adjust the air cylinder throttle valve to control the reciprocating speed of the piston rod, so that there is no impact or clamping stagnation when the air cylinder acts [6].

Design of PLC Control Circuit (1) Selection of PLC
The design of PLC control circuit must be based on the requirements of the task and the number of input and output points, select the PLC model and complete the I/O distribution, and draw the PLC control circuit diagram.
(2) Drawing of control circuit diagram A circuit diagram is a schematic representation of circuit composition and physical connection information, using graphical symbols to represent components and connections, with emphasis on function without regard to the physical size, shape, or location of the item.The circuit diagram should be drawn in accordance with GB/T 6988.1-2008 or JB/2740-2008 and JB/2739-2008 [7].

PLC Control Program (1) Start/stop control
The start/stop flow chart of the system is shown in Figure 4. 1) After the PLC is powered on and initialized, It checks whether the equipment has material shortage or material shortage fault in each scanning cycle, and calls the "status display" subprogram to display the current status of the system through the indicator light.Then it is divided into two branches according to the current operation state (start or stop).
2) If the current operation status is OFF, the system enters the startup operation process to complete the system startup.
3)If the current running state is ON, the system performs stepping sequence control, and monitors whether the stop button is pressed or whether there is a material shortage fault in each scanning cycle.If the material is insufficient, a stop command is sent out, and when the stepping sequence control returns to the initial step, the system operation is stopped.The main working process of the feeding unit is feeding control, which is a single-sequence step-by-step sequential control process.The programming method of step sequence control can be realized by shift instruction, decoding instruction, etc., and can also be realized by step instructions.
Step instructions are convenient when step control requires more complex selections, parallel branches, and jumps [8].The flow chart of stepping process is shown in Fig. 5.
Figure 5.The flow chart of stepping process 6. Summary (1) The installation and commissioning of the feeding system shall be carried out in the following order [9]: mechanical parts installation--gas circuit connection and adjustment--circuit wiring--sensor commissioning and circuit verification--PLC programming and commissioning.
(2) Before the pushing operation, the upper layer workpiece must be pressed by the top cylinder, and then the pushing cylinder is driven.
(3) The ejection completion signal is provided by the magnetic switch for detecting the ejection in place.However, when there is only one workpiece left in the silo, the top cylinder has no material to eject, so the ejection in place signal is fleeting.At this time, it is necessary to consider obtaining the ladder diagram of the falling edge signal [10].

Figure 1 .
Figure 1.Main Structure of Feeding Unit Figure 2. Feeding operation diagram

Figure 3 .
Figure 3. Pneumatic control circuit of feeding unit

Figure 4 .
Figure 4. Flow chart of start/stop control (2) Programming of Stepping Sequence Control ProcessThe main working process of the feeding unit is feeding control, which is a single-sequence step-by-step sequential control process.