專用銑床液壓系統(tǒng)設(shè)計
專用銑床液壓系統(tǒng)設(shè)計,專用銑床液壓系統(tǒng)設(shè)計,專用,銑床,液壓,系統(tǒng),設(shè)計
n Appication of hydraulic AGC and
width control to a hot strip mill
D.Alan Davies,Project Sale Manager,Engineering and Construction Div. Davy Mckee (Sheffie id)Lid, Sheffieid, U. K.
THE Pohang Iron & Steel Co.(POSCO) No.2 hot strip mill at Pohang, South Korea,is a modern, three-quarter continuous mill built by Mitsubishi in 1980.The mill is 2050mm wide,has four roughing stands and seven finishing srands.The seven finishing srands have a combined power of 56,000kw with a maximum strip speed of 21 metres/s.Coil weight is up to 35.3 tonnes. Annual mil capacity is 3.56 million tonnes.
To improve width and gage tolerances,POSCO decided to install hydraulic automatic width contol (HAWC) on the last edger (E4) and hydraulic automatic gage control (HAGC) on finishing stands F4 to F7.
Davy McKee's contract was for the total ackage associat-ed with modernization of the mechanical and hydraulic systems,the computer-bassd AWC/AGC controls, new widthmeter, mechanical installation, commissioning and training. The new equipment was put into service during a 14-day shutdown in 1987.
n Outline of new facilities
A priority requirement was that the new equipment should be integrated with the existing facility in such a way as to permit reversion to conventional operation in a few seconds. Accordingly, hydraulic AGC and AWC cylinders were designed to withstand normal rolling conditions when in a collapsed state.
All of the control systems had to be in parallel with the existing systems (which were retained ) and existing operator's desk contromechanical system, depending on which system was selected.
The AWC system comprises short-stroke, single-acting cylinders (four in total )engineered between the ends of the horizontal screwa and the vertical roll chocks . These cylinders are servo-controlled, with a stroke speed of 100 mm/s (4 ips) to provide in -bar width control. (With the bar being typically 50 mm thick at this stage, only a limited amount of correction was expected.)
A new widthmeter after roughing stand R3 is used to give feed forward control signals to the edger E4 AWC with the existing widthmeter after rougher R4 providing bar to bar updating .
The AGC system on the last four finishing stands has short-stroke, single-acting cylinders located between the top chocks and the acrewdown thrust bearing/load cell units.These cylinders have excetionally high dynamic performance (28 Hz ,10 mm/s velocity ).
Becayse of the physlcal distance between the edger E4 and the finishing stands F4 to F7 ,separate pump sets serve each atra ,The hydraulic pressure is 275 bars, mineral oil,with a filtration level of 3 microns .
The new computer configuration compries a network of seven PDP 11/73 microprocessors linked by an Ethernet highway . An unusual feature of the system was the need to tap into the existing 64-way parallel communications link between the existing supervisory control computer (SCC) and the melplac plc's which perform the screwdown AGC, The tap had to be transparent to existing communication and of a high integrity . (Hence a warm spare stand by computer was included in the system .)
The required data for the AGC/AWC was extracted , serialized and communicated to the new system along the Ethernet , highway , This had the advantage of opening up the computer system to easier communications in the future , as new systems could be attached easily to the Ethernet .(A few months later , a further contract for ENCO heat retention panels and interstand water curtains was retention panels and interstand water curtains was received which required a further 11/73 miceoprocessor .)
n Mechanical/hydraulic design features
AGC cylinders ---Various components of the AGC cylinders and their assembly are illustrated in Fig . 4,5 and 6.
The cylinder design incorporates a single , low -friction seal that constests of a Teflon band mounted on the piston below a bronze , side trust ring . The base of the piston is chamfered to give a rocking surface when the cylinder is used in a collapsed state .It gives the necessary degree of freedom to absorb the normal deflections in the mill .
A hydraulic manifold is mounted to the front of each cylinder that includes the servo-valves.One of the position transducers is slightly discernible behind the small accumulator .Another position transducer is fitted diametrically opposite . The two signals from the transducers are averaged to provide a mean stroke signal .
The transducer package is shown in .The Sonymagnescale transducers with 1 micron resolution are hermetically sealed insode the brass bodies .
Three-stage servo-valves are employed (Moog 79 series ) .The third stage has its own built-in closed-loop position control . Each valve is nominally rated at 230 litres /min . Two valves are fitted to each cylinder and operate electrically in cascade , ie , as the drive signal to the first valve reaches saturation , it spills over to the second valve . They have a frequency response of 200 Hz . Cylinder parameters and performance data are summarized in Table I .
Dynamic performance was checked on a similar cylinder (890 mm dia compared to 960 mm on the POSCO mill ) with identical transducers , servo-valves , etc , installed on a mill housing equipped as a test rig . Steel blocks accurately represent the masses of the chocks and rolls , giving a truerepresentation of the mass-spring conditions in a real mill . The frequency resonse as a function of the rolling load is illustrated in , Loop gain is automatically adjusted by the software to optimize the dynamics .
One of the inberent features of a single-acting cylinder design is that the flow rate through the servo-valves and , thus , the cylinder speeds , is a function of the actual pressure in the cylinder . To prevent unnecessarily high speeds at the higher and lower sections of the range , simple software rules limit the electrical drive signals to the servo-valves ,effectively creating a stable and symmetrical velocity performance in both the extending and retacting directions , over the working range of the cylinder .
AWC cylinders --The AWC cylinders have a thrust bearing with spherical seating , embedded into the piston . Each cylinder is served by its own 3-stage servo-valve located nearby . The servo-valves and position transducers are interchangeable with the AGC counterparts . Performance details are also summarized in Table 1 .
Collapse force is provided by pull-back cylinders acting on the roll chocks . These cylinders are controlled to maintain a constant , low , pull-back force during the body of the bar , but increasing to a higher value to assist in achieving the tail end antinecking feature .
n Hydraulic systems --Hydraulic pumpsets are located in the oil cellars . The system serving the HAGC on stands F4 to F7 comprises a stainless steel reservoir tank with gravity feed to four axoal piston pumps ( three duty , one standby ) that deliver at 275 bars ( 4000 psi ) .
Filtration throughout is 1 micron nominal ( 3 micron absolute ) with a separate oil cooler/filter unit supplied by a separate recirculation pump , drawing oil from the tank , through the filter /cooler and back to the tank .
Accumulator manifolds with 38-litre , high -pressure nitrogen-filled accumulators ( that supply the transient demands mill stand . These accumulators are mounted as close to their respective cylinders as practically possible , to maximize dynamic performance .
n Contol system hardware features
One of POSCO's major concerns was the integration of the new computer systems without jeopardizing the existing system . (The existing system was to remain service and be available as a standby facility at all times .)
The 64-bit parallel interface between the existing supervisory setup computer (SCC) and the PLC ( MELPLAC) responsible for screw AGC could not be expanded or duplicated .
The solution was to interpose a PDP 11/73 with its standard digital I/O equipment betweent the SCC and the MELPAC to act as a communications link (Fig .9 ) . Its function was simple . It read-in the data from the a SCC as 64-bit data , stored it in memory and passed it immediately out again as identical digital output to the MELPLAC . The same exchange occurs in reverse order when data is passed back to the SCC . At each transaction , the 64 bits are decoded and converted into serial form for distribution to the remainder of the new systom . Such data would include all PDI and sretup information .
Because of the extreme concern for reliability in this exchange , a standby PDP 11/73 was included .When not in use , the standby machine is available as a software development facility for the entire new system .
These two machines were installed and commissioned approximately four months before the main shutdown when their function , operation and reliability were established prior to the main commissioning .In the main 14-day shutdown , the remaining conputer systems were brought on -line , although the AWC was given a lower priority than the AGC . The overall system configuration is shown .
Functionally , the HAGC for four stands were split between two 11/73 microprocessors to give a reasonable compromise between cost and utilization . Approximately 40% of the processor capability remains unused .
The roll eccentricity compensation (REC ) microprocessor can be switched to serve any one of stands F4 and F7 , whichever is seen to have the most significant eccentricity input . Afurther microprocessor could sasily be added in the future ( the REC function is described later in more detail ) .
The functions of the coordinating and logging microprocessor are evident ; it organizes the data flow between the various processors on the Ethernet and analyzes , stores and points out engineering and production data .
n Control system operational features
AWC system --The AWC system has two functions ;
l Reduce end crop losses by minimizing under-width ends .
l Improve width tolerances in the body of the bar .
Since the edger concerned is E4 and the bar is comparatively thin ( approximately 50 mm ) , little can be done to improve necking already created by the previous roughing /edging stands .Nevertheless , a small improvement can be expected by avoiding further worsening through stand E4/R4 . This is accomplished by preopening the edger roll gap a calculated amount and then swiftly closing onto the target width as the head end enters the edger . A similar procedure occurs at the tail end , when the gap is quickly opened a calculated amount .
The loci of these fast cylinder movements (eg , linear , expontial , parabolic , etc ) can be chosen by the setup computer , as well as the required gap adjustment velocity and stroke length .
Accurate tracking of the approach of the head and tail end is essential . This is achieved by special hot metal detectors coupled with bar speed measurement .
In-bar width control has two modes : BISRA gagemeter , and feedforward . Although the potential for the former mode of control ( which relies on the accurate sensing of instantaneous roll force to reduce mill stretch ) was always considered limited , due to the high frictional forces relative to the low rolling loads , it was , nevertheless , investigated . It was found to be unsatisfactory for the reason stated .
The feedforward mode , utilizing incoming width error variations detected by a widthmeter after stand E3/R3 , was successful . It resulted in exit width variations , measured after stand E4/R4 , within +2.0 mm for 95% of the bar length , as measured by the new widthmeter in this location . This instrument is used to give bar to bar width updating to maintain system calibration . However , it is not used for in -bar monitor feedback , because the transport distances involved are a significant proportion of the bar length .
n Hydraulic AGC--The operational features included in the hydraulic AGC system can be divided into those that can be considered as conventional and those that have a novel element .
Conventional AGC features include : absolute and lock-on BISRA gagementer modes for each hydraulic stand ; variable mill modulus ; oil film compensation ; draft comensation and absolute or lock-on feedback monitor .
Absolute and lock-on BISRA gagemeter modes for each hydraulic stand are selectable either automatcally by the SCC or manually .
The BISRA gagemeter action artificially stiffens the mill modulus . This occurs because the feedback from the measured roll foece causes the AGC cylinders to extend to compensate for mill stretch . The amount of compensation can be varied from zero ( ie , no gagemeter action ) , which leaves the mill with its natural mechanical stiffness , to 100% which , in effect , increases the mill modulus to infinity . Each hydraulic stand can be given a stiffness value ( 0 to 100% ) either from the SCC or manually .
Dynamic oil film compensation is obtained by cylinder movement to correct for dynamic changes in the backup roll bearing oil-film thickness , which varies as a function of speed and roll load .
Every gage correcting movement of the AGC cylinders results in a strip mass-flow change that alters the looper angle which , in turn , requests the stand speed to change . This sequence is anticipated and effectively shot circuited by direct speed trim signals sent directly from the AGC .
With regard to absolute or lock-on feedback monitor ,stand F7 etit x-ray gage can be selected to back in either mode . In the former mode , the system continues to make corrections until the target gage is achieved . In the latter mode , the head-end gage is accepted and maintained consistently for the remainder of the coil .
Novel AGC features include : auto-steering ; distibuted monitor feedback ; and roll eccentricity compensation .
Auto-steering , in which the tendency for the strip to steer to one side as a consequence of uneven heating across its width , is opposed by the control system . The roll force difference side to side is measured and fed to a functional representation of the tilt modulus of the mill stand ( the measured mill modulus characteristic when the roll gap is tilted differentially ) . The output of this functional block represents the amount of roll stack tilt that must have taken place to cause the force difference . The correction , similar to BISRA gagemeter , then restores parallelism to the roll gap and , hance , improves strip tracking .
Feedback from the exit x -ray gage to stands F4 , F5 , F6 andF7 is , in itself , conventional . However , the novel feature of this approach is that the distribution of correction is calculated to cause incremental force changes at stands F4 to F7 in direct proportion to the original roll force pattern calculated by the SCC . This minimizes the disturbance to profile and shape ( Fig .10 ) .Calculation of factors x , y and z take into account the following pattern ; required force distribution pattern ; percentage gagemeter set at each stand ; and calculated material stiffness at each stand .
The eccentricity of the backup rolls and bearings can cause a significant imprint in the material being rolled , particularly with gagemeter AGC , where the mill stands behave as if they were infinitely stiff .
Roll eccentricity is a complex function , generally different for top and bottom rolls , and from side to side . The resulting waveform is multivariable , changes with time and exhibits high frequency components ( up to 5th harmonic ) caused by bearing key effects .
The requirements for an effective automatic roll eccentricity compensation ( REC ) system are :
l Dynamic to follow the changing pattern .
l Cappble of isolating and identifying top and bottom backup roll effects , and the drive side and roll change side effects (ie , 4-axis operation ) .
l AGC cylinder response is sufficiently fast to respond to the REC system demands and counteract the disturbances .
A block diagram of the system is shown in Fig . 11 .
n Performance
Early equipment reliability problems , generally associated with the high shock forces created as this high-speed mill threads and tails-out , have been resolved for the most part with minimum loss of productivity due to the ability to revert almost instantaneously to the old system
The AWC system achieved its target of 95% bar length within +2 mm .
AGC performance for the coil body is well within + 0.050 mm (+ 0.002 in . ) . Occasional misses at the head end are attributable to mill setup . A new scheduling and setup computer system is to be installed .
Data collected over a 2-week period in March 1998 , covering approximately 3900 coils , showed that close to 96% of light gage coil lengths were within +0.035 mm (+0.00138 in . ) and that , for heavier gages (up to 6 mm ) , close to 95% of coil lengths were within +0.045 mm ( +0.00177 in . ) . ( These lengths refer to the coil lengths after exclusion of the first and last 5 metres of each coil . )
n Summary
The AWC and AGC systems , incorporating many new hardware and software features , with extremly exacting performance requirements , have met their objectives of improving strip quality .The potentially difficult area of interfacing with existing computer systems , while retaining their integrity , was accomplished through extensive planning and design .
n 對電控帶式銑床運用液壓
自動精度控制和寬度控制
戴維斯.艾倫博士，英國謝菲爾德股份有限公司工程與建筑部門項目經(jīng)理及營業(yè)主任。戴維.麥凱，英國謝菲爾德股份有限公司 。
在韓國南部浦項鋼鐵公司第二分公司的電控帶式銑床是在1980年建造的現(xiàn)代的，四分之三的連續(xù)的銑床。該銑床工作臺寬2050mm，能進行4次粗加工和7次精加工，其帶的最大速度 21m/s ,此時的總功率為 56,000kw.限卷重量是達 35.3噸以上。 該銑床的年產(chǎn)量為356萬噸。
為了改善加工寬度和精度公差， 浦項鋼鐵公司決定在尾末的修邊機安裝液壓自動控制(HAWC)，并在精加工F4-F7處安裝液壓自動精度控制 (HAGC) 。
戴維.麥凱的任務(wù)是將現(xiàn)代化的機械系統(tǒng)和液壓系統(tǒng)連接在總體機器上，利用計算機建立 AWC/AGC的控制，實現(xiàn)新的寬度，機械的安裝,進行試車訓(xùn)練。 新的機器在1987年在14 天的截止期間投入使用。
n 新設(shè)備的概述
一個先決條件是新的設(shè)備必須結(jié)合現(xiàn)有設(shè)備尋求一個方法，在很少次品的基礎(chǔ)上運用傳統(tǒng)操作實現(xiàn)反轉(zhuǎn)。 因此，液壓AGC和AWC氣缸設(shè)計成產(chǎn)生失穩(wěn)狀態(tài)時能夠抵擋正常的滾動。
所有的控制系統(tǒng)依靠被挑選的系統(tǒng)與現(xiàn)有系統(tǒng)保持平行，現(xiàn)有的操作員在實驗臺控制時,必須熟練地操作任何液壓系統(tǒng)和機電系統(tǒng)。
AWC 系統(tǒng)包含短行程,單作用氣缸設(shè)計在水平螺桿的后面與垂直滾動止動器之間，該氣缸是伺服控制的,以行程速度為100毫米/s提供在緩沖地址寄存器中的寬度控制，并且實現(xiàn)了頂部量器和尾部刀槽的效果控制。
在粗加工實驗臺R3后的一些寬度量具過去習(xí)慣于給正向反饋電傳送控制信號對修邊機E4進行自動寬度控制，現(xiàn)在現(xiàn)行的寬度量具在粗加工設(shè)備R4后，只需要面對面地調(diào)整。
自動精度控制系統(tǒng)在最后4次精加工中被設(shè)為短行程，單作用氣缸被定位在頂部止動器與螺桿下方的牽引軸承/載荷單元之間。這些氣缸具有異常的動態(tài)性能（28Hz,速度10mm/s).
由于實際距離在修邊機E4與精加工F4至F7之間，分離泵的總成裝配能供應(yīng)到每一個地方。液壓設(shè)備需要壓力為275 bar,具有3微米過濾水平的礦物油。
新的計算機配置包含在以太網(wǎng)總線上連接7個程序數(shù)據(jù)處理機和11/73微理器處，系統(tǒng)的不同的零件需要被連接在現(xiàn)有的計算機監(jiān)督管理機構(gòu)（SCC）和可編程邏輯控制器（PLC)之間的現(xiàn)有的64位通訊端口上。再這之上有被透視的現(xiàn)有通訊和高速結(jié)構(gòu)（因此，現(xiàn)有的計算機系統(tǒng)包含有升溫設(shè)備站）。
給自動寬度控制/自動精度控制（AGC/AWC）的必須的數(shù)據(jù)被提取，并沿著以太網(wǎng)總線被連續(xù)的傳達給新系統(tǒng)。將來，如同新系統(tǒng)能簡單地被綁到以太網(wǎng)上那樣，這樣具有給計算機系統(tǒng)開墾更簡單的通信的優(yōu)點（兩三個月以后，更進一步的契約給ENCO加熱保留了展示板，并且，更多11/73微處理器必須的中間機座的云狀水紋被受到）。
n 機械/液壓的設(shè)計特點
自動精度控制（AGC）氣缸--自動精度控制（AGC）氣缸以及它們的部件的各種零件的視圖。
氣缸設(shè)計為單一的整體，低摩擦的封口的聚四氟乙烯萬能插孔帶被懸掛在青銅下的活塞上。當(dāng)氣缸處于失穩(wěn)狀態(tài)時基準(zhǔn)活塞被傾斜用于調(diào)節(jié)擺動曲面。在進行銑削時，反饋正常的偏差以達到所需要的自由度。
液壓管被安裝在每個氣缸的前面，包括伺服閥。其中一個位置檢測器在小型蓄力器之后稍稍可被辨別。其中一個位置檢測器在其正對面作配合使用。兩個信號從檢測器被平均地提供平均行程信號。
檢測器組件見。具有1微米分辨率的索尼magnescale 檢測器被密封在黃銅體內(nèi)。
第三類伺服閥被運用（穆格79系列）。第三類伺服閥有它自己的內(nèi)置組合式閉合環(huán)進行位置控制。每個閥的理論額定流量為2230升/分。兩個閥被配合每個氣缸安裝，并且被電線串聯(lián)運行。在工業(yè)工程學(xué)上，相當(dāng)于傳動信號從最初的閥到達極限，并且遠遠超過第二類閥。他們具有200Hz的頻響應(yīng)率響應(yīng)，提供給所有28Hz的氣缸。氣缸參數(shù)和性能數(shù)據(jù)見表I。
其動態(tài)的性能的檢測是：將其安裝在相當(dāng)于試驗設(shè)備的軋機機架裝備上，在一個類似氣缸上進行檢驗（浦項鋼鐵公司銑床上,直徑890mm與960mm比較），伴隨完全一樣的檢測器，伺服閥等等。鋼塊準(zhǔn)確的表現(xiàn)了止動塊和滾子的質(zhì)量，給出質(zhì)量彈簧在實際銑削條件下的實際表達。頻率響應(yīng)相當(dāng)于載荷滾壓的作用，。環(huán)路增益通過動力學(xué)最優(yōu)化軟件自動校準(zhǔn)。
一個單作用氣缸設(shè)計的固有特點是流動速率通過伺服閥被測定，因此氣缸的速率說明了氣缸的實際壓力。在氣缸的整個工作范圍內(nèi)，在較高和較低區(qū)域的范圍內(nèi)，為了防止不必要的高速率，用簡單的軟件規(guī)則把電傳動限制在伺服閥范圍內(nèi)，并在延伸和收縮兩個方向有效地產(chǎn)生穩(wěn)定的，對稱的速度性能。
自動寬度控制（AWC）氣缸------AWC氣缸具有一個有球形座的止推軸承和壓入活塞。每個氣缸均可以通過它附近的自身帶的第三類伺服閥確定并使用。伺服閥和位置傳感器可與自動精度控制（AGC）相對的部位相互交換。性能細節(jié)見表1。
條 件
氣 缸
自動精度控制（AGC）
自動寬度控制（AWC）
內(nèi)徑（mm）
980
350
行程(mm)
30
5
收藏