基于PLC的組合機(jī)床控制系統(tǒng)設(shè)計(jì)【含5張CAD圖紙+文檔資料】
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PLC Question
PLC which should pay attention in the application is specially the control device which serves for the industrial production, usually does not need to take any measure, may use directly in the industry environment. But, when the production environment is too bad, the electromagnetic interference is special intense, or installs uses improper, cannot guarantee PLC the normal operation, therefore should pay attention to the following question in the use.
First, working conditions
(1) Temperature
The PLC requests ambient temperature when 0~55℃, installs cannot
place under the calorific capacity big part, all around ventilates the radiation the space to be big enough, between the elemental area and the expansion unit must have above 30mm to be separated; On the switch cabinet, lower part should have the well ventilated louver, prevents the sunlight direct radiation; If the environment surpasses 55℃, must install the electric fan forced ventilation.
(2)Humidity
PLC in order to ensure insulation performance, air relative humidity should be less than 85% (no Gel).
(3) Vibration
PLC should be far away from the intense vibration source, prevents the vibration frequency is 10~55Hz frequent or the vibration. When use environment inevitable vibration, must take the absorption of shock measure, like uses the absorption of shock rubber and so on.
(4)Air
In order to avoid corrosion and flammable gases, such as hydrogen chloride, hydrogen sulfide and so on. The more the air of dust or corrosive gas environment can be installed in a closed PLC better control of the control room or cabinet, and install air cleaning devices.
(5) Power Supply
PLC power supply is 50Hz, 220 (1 ± 10%) V AC, for the power line interference, PLC itself has sufficient capacity to resist. Reliability requirements for high power occasion or a particularly serious environmental interference, you can install a shield with variable ratio of 1:1 isolating transformers, in order to reduce the interference between the equipment and the earth .Also can input in the power series of LC filter circuit.
Second, installment and wiring
(1) The power line, the pilot wire as well as the PLC power line and the I/O line should distinguish the wiring, between the insulating transformer and PLC and I/O should use the double rubberized wire connection.
(2) PLC should be far away from the strong jamming source like electric welding machine, the high efficiency silicon rectifier unit and the large-scale power equipment, cannot install with the high-pressured electric appliance in the identical switch cabinet.
(3) The input and output of PLC are best separate the line, the switch quantity and the simulation quantity must separate the placing. The simulation quantity signal's transmission should use the shielded wire, the shielding layer should an end or the both sides earth, and the earth resistance should be smaller than the shielding layer resistance 1/10.
(4) The PLC elemental area and the expansion unit as well as functional module's ties cable should lie alone, prevents the outside signal the disturbance.
(5) The exchange output line and the direct-current output line do not use the identical root electric cable, the output line to be far away from the high tension line and the power line as far as possible, avoids parallel.
Third, I/O end wiring
1. Input wiring (1) inputs the wiring not to surpass 30 meters generally. But if the environment disturbance is small, when the loss of voltage is not big, the input wiring may suitable long.
(2)Inputs/the output line not to be able to use the identical root electric cable, the input/output line to be separated.
(3)Uses the normally opened contact form to connect the input end as far as possible, causes the establishment the trapezoidal chart to be consistent with the relay schematic diagram, is advantageous for reading.
2. Outgoing junction
(1) The out-put wiring divides into the independent output and the public output. In not group, may use the different type and the voltage class output voltage. But can only use the identical type, the identical voltage class power source in the identical group's output.
(2) Because the PLC output element is sealed on the print circuit wafer, and connects to the terminal strip, if will connect output element's load short circuit, will burn down the print circuit wafer, therefore, application fuse protection output element.
(3)Uses when the relay outputs, withstands inductive load's size, will affect relay's service life, therefore, time use inductive load the selective relay working life must be long.
(4) The PLC output load possibly has the disturbance, must therefore take the measure to control, if direct-current output's after flow guarantees protects, the exchange output anti- accommodates the absorbing circuit, the transistor and the bidirectional thruster output by-passed resistor protection.
Fourth, outside security electric circuit to guarantee that the overall system can under the secure state the reliable work, avoids, because the external power supply breaks down, PLC to present the heavy economic loss which and the person casualty exceptionally, the disoperation as well as outputs by mistake creates, PLC the outside should install the essential protection circuit.
(1) Stops the electric circuit anxiously. Regarding can cause the user to cause the damage the dangerous load, besides performs in the control procedure to consider, but also exterior should design the emergency stop electric circuit, causes when PLC breaks down, can cause the injury load power source reliably to shut off.
(2)Fragment. The forward and reverse revolution and so on reversible operation's control system must establish the exterior electric appliance interlock protection; the reciprocation moves and rises and falls motion the control system, must establish the exterior spacing protection circuit.
(3)The programmable controller has self-checking functions and so on surveillance timer, when inspects exceptionally, outputs completely the closure. But when programmable controller CPU breakdown cannot control the output, therefore, regarding can cause the user to cause the damage the dangerous load, to guarantee that the equipment moves under the secure state, must design the external circuit to protect.
(4) Power source load protection. If the PLC power source breaks down, the interruption interval is short in 10 seconds, PLC works not affected, if the power source interrupt surpasses 10 second or the power source drops surpasses the permissible value, then the PLC stop work, all output also separates; when the power source restores, if RUN input connection, then operates carries on automatically. Therefore, to establish the essential current limiting protection circuit to some easy over-loading's input device.
(5) Significant breakdown warning and protection. Regarding easy to have heavy accident's place, to guarantee the control system when the heavy accident occurs still the reliable warning and the protection, should have with the significant breakdown the contacting signal to output through the external circuit, caused the control system to move under the safe condition.
Fifth, PLC earth the good earth is guaranteed that the PLC reliable work the important condition, may avoid the heterogametic the voltage surge harm. PLC meets the grounding and machine's ground terminal docking, meets the grounding the cross-sectional area should not to be smaller than 2mm2, the earth resistance is smaller than 100Ω; If must use the expansion unit, its ground point should accept after checking with the elemental area earth in the same place. In order to suppress adds in the power source and the input end, out-port's disturbance, should joins the special-purpose grounding to PLC, the ground point should with the power equipment (for example electrical machinery) the ground point separate; If cannot meet this kind of requirements, must achieve with the other equipment public earth, forbids to establish contacts the earth with other equipment. The ground point should approach PLC as far as possible.
PLC 在應(yīng)用中應(yīng)注意的問題
PLC是專門為工業(yè)生產(chǎn)服務(wù)的控制裝置，通常不需要采取什么措施，就可以直接在工業(yè)環(huán)境中使用。但是，當(dāng)生產(chǎn)環(huán)境過于惡劣，電磁干擾特別強(qiáng)烈，或安裝使用不當(dāng)，都不能保證PLC的正常運(yùn)行，因此在使用中應(yīng)注意以下問題。
一、工作環(huán)境
1． 溫度
PLC要求環(huán)境溫度在0~55℃，安裝時(shí)不能放在發(fā)熱量大的元件下面，四周通風(fēng)散熱的空間應(yīng)足 夠大，基本單元和擴(kuò)展單元之間要有30mm以上間隔；開關(guān)柜上、下部應(yīng)有通風(fēng)的百葉窗，防止太陽光直接照射；如果周圍環(huán)境超過55℃，要安裝電風(fēng)扇強(qiáng)迫通風(fēng)。
2． 濕度
為了保證PLC的絕緣性能，空氣的相對(duì)濕度應(yīng)小于85%（無凝露）。
3． 震動(dòng)
應(yīng)使PLC遠(yuǎn)離強(qiáng)烈的震動(dòng)源，防止振動(dòng)頻率為10~55Hz的頻繁或連續(xù)振動(dòng)。當(dāng)使用環(huán)境不可避 免震動(dòng)時(shí)，必須采取減震措施，如采用減震膠等。
4． 空氣
避免有腐蝕和易燃的氣體，例如氯化氫、硫化氫等。對(duì)于空氣中有較多粉塵或腐蝕性氣體的環(huán)境，可將PLC安裝在封閉性較好的控制室或控制柜中，并安裝空氣凈化裝置。 5． 電源
PLC供電電源為50Hz、220（1±10%）V的交流電，對(duì)于電源線來的干擾，PLC本身具有足夠的抵制能力。對(duì)于可靠性要求很高的場合或電源干擾特別嚴(yán)重的環(huán)境，可以安裝一臺(tái)帶屏蔽層的變比為1：1的隔離變壓器，以減少設(shè)備與地之間的干擾。還可以在電源輸入端串接LC濾波電路。
二、安裝與布線
1． 動(dòng)力線、控制線以及PLC的電源線和I/O線應(yīng)分別配線，隔離變壓器與PLC和I/O之間應(yīng)采用雙膠線連接。
2． PLC應(yīng)遠(yuǎn)離強(qiáng)干擾源如電焊機(jī)、大功率硅整流裝置和大型動(dòng)力設(shè)備，不能與高壓電器安裝在同一個(gè)開關(guān)柜內(nèi)。
3． PLC的輸入與輸出最好分開走線，開關(guān)量與模擬量也要分開敷設(shè)。模擬量信號(hào)的傳送應(yīng)采用屏蔽線，屏蔽層應(yīng)一端或兩端接地，接地電阻應(yīng)小于屏蔽層電阻的1/10。
4． PLC基本單元與擴(kuò)展單元以及功能模塊的連接線纜應(yīng)單獨(dú)敷設(shè)，以防止外界信號(hào)的干擾。
5． 交流輸出線和直流輸出線不要用同一根電纜，輸出線應(yīng)盡量遠(yuǎn)離高壓線和動(dòng)力線，避免并行。
三、I/O端的接線
1． 輸入接線
?。?）輸入接線一般不要超過30米。但如果環(huán)境干擾較小，電壓降不大時(shí)，輸入接線可適當(dāng)長些。（2）輸入/輸出線不能用同一根電纜，輸入/輸出線要分開。（3）盡可能采用常開觸點(diǎn)形式連接到輸入端，使編制的梯形圖與繼電器原理圖一致，便于閱讀。
2． 輸出連接
?。?）輸出端接線分為獨(dú)立輸出和公共輸出。在不同組中，可采用不同類型和電壓等級(jí)的輸出電壓。但在同一組中的輸出只能用同一類型、同一電壓等級(jí)的電源。（2）由于PLC的輸出元件被封裝在印制電路板上，并且連接至端子板，若將連接輸出元件的負(fù)載短路，將燒毀印制電路板，因此，應(yīng)用熔絲保護(hù)輸出元件。（3）采用繼電器輸出時(shí)，所承受的電感性負(fù)載的大小，會(huì)影響到繼電器的使用壽命，因此，使用電感性負(fù)載時(shí)選擇繼電器工作壽命要長。（4）PLC的輸出負(fù)載可能產(chǎn)生干擾，因此要采取措施加以控制，如直流輸出的續(xù)流管保護(hù)，交流輸出的阻容吸收電路，晶體管及雙向晶閘管輸出的旁路電阻保護(hù)。
四、外部安全電路
為了確保整個(gè)系統(tǒng)能在安全狀態(tài)下可靠工作，避免由于外部電源發(fā)生故障、PLC出現(xiàn)異常、誤操作以及誤輸出造成的重大經(jīng)濟(jì)損失和人身傷亡事故，PLC外部應(yīng)安裝必要的保護(hù)電路。
?。?）急停電路。對(duì)于能使用戶造成傷害的危險(xiǎn)負(fù)載，除了在控制程序中加以考慮之外，還應(yīng)設(shè)計(jì)外部緊急停車電路，使得PLC發(fā)生故障時(shí)，能將引起傷害的負(fù)載電源可靠切斷。（2）保護(hù)電路。正反向運(yùn)轉(zhuǎn)等可逆操作的控制系統(tǒng)，要設(shè)置外部電器互鎖保護(hù)；往復(fù)運(yùn)行及升降移動(dòng)的控制系統(tǒng)，要設(shè)置外部限位保護(hù)電路。（3）可編程控制器有監(jiān)視定時(shí)器等自檢功能，檢查出異常時(shí)，輸出全部關(guān)閉。但當(dāng)可編程控制器CPU故障時(shí)就不能控制輸出，因此，對(duì)于能使用戶造成傷害的危險(xiǎn)負(fù)載，為確保設(shè)備在安全狀態(tài)下運(yùn)行，需設(shè)計(jì)外電路加以防護(hù)。（4）電源過負(fù)荷的防護(hù)。如果PLC電源發(fā)生故障，中斷時(shí)間少于10秒，PLC工作不受影響，若電源中斷超過10秒或電源下降超過允許值，則PLC停止工作，所有的輸出點(diǎn)均同時(shí)斷開；當(dāng)電源恢復(fù)時(shí)，若RUN輸入接通，則操作自動(dòng)進(jìn)行。因此，對(duì)一些易過負(fù)載的輸入設(shè)備應(yīng)設(shè)置必要的限流保護(hù)電路。（5）重大故障的報(bào)警及防護(hù)。對(duì)于易發(fā)生重大事故的場所，為了確?？刂葡到y(tǒng)在重大事故發(fā)生時(shí)仍可靠的報(bào)警及防護(hù)，應(yīng)將與重大故障有聯(lián)系的信號(hào)通過外電路輸出，以使控制系統(tǒng)在安全狀況下運(yùn)行。
五、PLC的接地
良好的接地是保證PLC可靠工作的重要條件，可以避免偶然發(fā)生的電壓沖擊危害。PLC的接地線與機(jī)器的接地端相接，接地線的截面積應(yīng)不小于2mm2 ，接地電阻小于100Ω；如果要用擴(kuò)展單元，其接地點(diǎn)應(yīng)與基本單元的接地點(diǎn)接在一起。為了抑制加在電源及輸入端、輸出端的干擾，應(yīng)給PLC接上專用地線，接地點(diǎn)應(yīng)與動(dòng)力設(shè)備（如電機(jī)）的接地點(diǎn)分開；若達(dá)不到這種要求，也必須做到與其它設(shè)備公共接地，禁止與其它設(shè)備串連接地。接地點(diǎn)應(yīng)盡可能靠近PLC。
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