Keywords: anchor chain, circular knitting machine, PLC control system
China Library Classification Number: TG146.21; +0; TG 156.2 document identification number: a.
Anchor chain manufacturing equipment, namely anchor chain production line, is an anchor chain production line composed of heater, ring knitting machine, preheating flash butt welding machine, deburring machine, gear press, turntable and so on. The heater is used to heat the straight bar meeting the processing length to the temperature required for processing. Ring knitting machine is to shape the heated straight bar twice, bend it into the shape of an open link, and then connect it with other made links to form a chain. Then the open loop is welded into a closed loop by preheating flash butt welding on the welding machine. The deburring machine is used to remove burrs formed at welded joints after welding. Finally, the deburred link is formed on the press, and the rung is pressed in the middle of the link. At this point, the production of a link is completed, and then the completed link is rotated to the front of the ring knitting machine equipment by the turntable equipment, ready to be connected with the link of the next ring to be bent. The final product is shown in figure 1. Among them, the braiding machine is the most complicated equipment in the whole anchor chain production line.
1 process introduction
The process flow of the anchor chain looper is that the rotating mechanism of the fixture III is reset, and the fixture I moves forward to send the hot rod into the jaw of the center push rod; The central push rod is closed, and the locking mechanism locks the central push rod; When the sliding beam advances for the first time, the left and right shaping arms begin to clamp, and the left and right clamping arms are reset after shaping; Then the sliding beam returns to reset; Open the locking mechanism of the central push rod and unlock it, at the same time, the second tong drags the mechanism forward, the second tong clamping mechanism clamps the bar, and then open the closing mechanism of the central push rod; Loosen that clamping mechanism of the clamp II, and rotate the bar by 90 degrees through the rotation of the clamp III; The clamping mechanism of fixture II clamps the bar again and drags the bar to a proper position until the lower half ring bends. At this point, the first forming action is completed, and the straight rod is bent into an upper semi-ring. In the process of the second molding action, at the same time, the link made last time is sleeved in this semi-ring, thus completing the process of "weaving" the ring, and weaving the link together to form a chain shape.
PLC control system of anchor chain ring knitting machine
Because of the single production equipment, small scale and relatively concentrated control objects, a single PLC control can meet the requirements. Because there are many I/O points, you can choose the appropriate I/O expansion unit. Moreover, there are no special requirements for digital storage, display, networking and transmission, and there are no analog signals. This design plans to choose the single-machine control mode of PLC basic unit plus expansion unit. The structural composition is shown in figure 1:
2. 1 Determination of control mode and PLC model and function module
Because the ring knitting machine has single production equipment, small scale and centralized control objects, it is not necessary to store, display and transmit numbers. According to the content introduced in the section of "Basic Structure of PLC" above, this design plans to choose the basic unit of PLC plus extended single machine control mode. Determination of PLC model: the number of I/O points is one of the basic parameters for selecting PLC. As mentioned above, the input of the control system is 4 1 point and the output is 20 points. There are more input points than output points, so the structure of basic unit plus I/O expansion unit is selected. As shown in Table 3 below, FX2n-64 is the most suitable choice. There is no need to expand the output point, only need to add the input unit. In order to ensure the appropriate margin of input points, it is more appropriate to add a 16 point input expansion unit. In this way, the input point * * * is 48 points and the output point * * * is 32 points. The actual input point is 4 1 point and the output point is 20 points. Considering the influence of harsh environment, high temperature, metal dust, oil pollution, strong electromagnetic interference and other factors in the control site, the input and output power supply adopts DC24V, and the output adopts relay output mode. The mechanical isolation of contacts can effectively avoid the strong electromagnetic interference of off-site circuits.
2.2PLC control circuit design
The PLC control loop * * * consists of control power supply design, PLC control input loop design, PLC control output loop design, PLC control cabinet electrical layout design, coil knitting machine operation box electrical layout design, field wiring diagram and other parts. The power supply of control loop needs two kinds of power supply, one is AC220V power frequency power supply, which supplies power to PLC. One is DC24V power supply, which supplies power to solenoid valve. The main switches of PLC and solenoid valve are small low-voltage circuit breakers QF 1 and QF2 respectively, and they have short-circuit protection function. FU 1 and FU2 are specially used for short-circuit protection of PLC. Every common junction of the output circuit is designed with insurance, which can spread the risk of power failure of the whole control circuit caused by field short circuit. In order to prevent the interference and impact of power grid circuit on PLC and ensure the normal operation of PLC, an isolation transformer is added at the power input end. Selection of isolation transformer capacity: FX2n-64 has a capacity of 60VA, and appropriate answers should be considered when selecting isolation transformer, so BK- 100VA isolation transformer is selected.
There are two input circuits, one is contact switch type, and the other is proximity switch type.
Working principle of contact switch input circuit. As shown in the schematic diagram of the input interface circuit in Figure 2, when the input contact K0 is closed, a current loop is formed between DC24V and 0V in PLC through the photoelectric coupling device, the current limiting resistor and the input contact, and the output of the photoelectric coupling device is "1", and the signal input of "1" is obtained in PLC. The working principle of the proximity switch type input loop is that when the sensing block approaches the proximity switch, the NPN proximity switch is in a conducting state, and the DC24V inside the PLC passes through the photoelectric coupling device, the current limiting resistor and the X 10 input contact, and returns to the common * * * terminal COM through the NPN proximity switch collector to form a current loop. The output of photoelectric coupling device is "1", and the internal DC of PLC gets "65438+".
3PLC ladder diagram program design
Program function requirements:
1) loop operation can realize manual operation and automatic operation.
2) Automatic operation is divided into two stages. The foot switch I controls the first molding action; Pedal Ⅱ controls the second molding action. These two molding actions should be interlocked. In the first molding work, even if you step on the second foot by mistake, you will not react to the second molding action. Similarly, if you step on the first foot by mistake in the second molding work, you will not react to the first molding action.
3) In the process of two molding operations, if there is any accident, you can press the stop key at any time to terminate the automatic process; At this time, the "manual/automatic" switch can also be switched to "manual", and the molding action is terminated. After handling the unexpected situation, turn the switch to "Automatic" again, and the program will continue after the last action.
4) The forward and backward movements of the same cylinder are interlocked by software to prevent misoperation.
5) After the left and right plastic arms are in place, they can return separately. As long as one is not in place, the other must wait until it is in place (so as to ensure that the plastic surgery is in place).
Section 2.2 describes the logical sequence and will not be repeated.
label
After many revisions, the program has been repeatedly tested and debugged in GX simulation software environment, and it runs stably, which can fully ensure the on-site production and provide guarantee for the continuous and stable production of enterprises.
refer to
[1] Pan Huiqing. Fault Treatment of PLC Control System of Mine Hoist [J]. Energy and Environment, 20 12(0 1).
Wu. Circuit design of four-phase stepping motor based on PLC [J]. Digital technology and application, 20 12(0 1).