Digital hydraulic control system for automatic thickness control of medium plate rolling mill
In the plate rolling mill is the key equipment. With the product performance requirements continue to increase, the electric pressure early, has been increasingly unable to meet the production requirements, so the hydraulic AGC (automatic gauge control) have been widely used, now usually adopts electro-hydraulic servo system, this system uses analog control and servo valve control, analog control system complex transmission links, A/D and D/A conversion of analog signal, poor anti-interference ability, difficult debugging, servo system of oil cleanliness requirements, anti pollution ability is weak, coupled with the temperature falling float, so they increased the debugging and maintenance difficulty, because of this complex system, so the price general manufacturers are difficult to bear. With the development of science and technology, a performance price ratio of plate mill of superior oil AGC digital hydraulic control the advent of new technologies. The principle and characteristics of this system are summarized: |
This system by the general electric APC (automatic position control) and hydraulic AGC (automatic gauge control), it is characterized by the transformation for the old mill, only a very small set of stroke dry oil master cylinder and oil pressure cylinder can be digital, its working principle is: first by the technical personnel to the steel preparation and rolling pass reduction arrangement, and the list is sent to the computer, when a steel rolling, rolling out directly by the operator, rolling, the computer gives each rolling thickness, when the computer is given value and detect the displacement sensor of pressure screw on the set value of the approach, computer control of Screwdown Motor speed and accurate parking, ensuring the electric APC has a high precision of the stop position (i.e. the gap position), when APC is in place, start rolling, the dry cylinder pressure sensor detection A pressure signal, when the signal is stable, can immediately deliver the signal into a hydraulic AGC setting, do not switch into the hydraulic AGC, when the rolling force increases, due to the elastic deformation of the rack, roll gap will appear small changes, while dry cylinder is compressed, the micro displacement of the small displacement. Amplified (usually 10 times) after moving thin oil cylinder rod, and then through mechanical connection open digital valve valve port, automatically increase the pressure, the digital cylinder cavity after compression, due to high pressure gain digital valve, thus moving small amount (about 0.05mm), so as to maintain the master cylinder position almost unchanged (about 0.005mm), the formation of a set of hydraulic AGC automatic position closed-loop constant roll gap control system, at the same time, the head pressure measured rolling force variation immediately entered into the computer, the computer through mathematical computation, output immediately Pulse string, the actions of the digital control pressurization cylinder and the rolling force variation caused by the frame on elastic deformation compensation, which is a set of online electric feedback system, its purpose is compensation rolling force variations caused by the roll gap variation, so as to ensure the products always control the tolerance range and to improve sheet in poor accuracy.
The pilot stage of digital hydraulic cylinder through dry cylinder force and improve the accuracy, can achieve micron level and tons of AGC control.
Case: digital hydraulic AGC program is as follows:
In order to reduce the reconstruction workload, reduce risk, and try to keep the integrity of the original system, and the scheme will dilute the oil pressure cylinder for digital processing, as shown in figure increased feedback rod in dilute oil cylinder after the cylinder rod, the rod nut is connected through the feedback coupling and digital valve, direct position feedback, to achieve machine - liquid AGC closed loop, and the stepping motor drives the valve core to rotate, the coupling nut, spool axial movement, change before and after the pressure cylinder cavity pressure, the booster cylinder moves the mobile through the feedback mechanism to close the valve port, the distance of each movement and digital pulse train number one one corresponding to each (such as 0.03mm/ although this method is better than pulse), the direct use of digital cylinder for existing oil pressure cylinder is convenient, but in the current oil pressure cylinder of incomplete information, connecting dimensions is not clear Dry, oil seal length is unknown, is the most simple and reliable method for reconstruction.
This system has several major characteristics:
Digital hydraulic APC can accurately and quickly adjust to the set value and is open loop digital control with fast response and high precision.
Digital hydraulic AGC turbocharged parts, the main cylinder of its pulse adjustment accuracy of up to 0.003mm, the high accuracy and great power to unite.
Debugging convenient. In this system, roll gap meter only APC adjustment when in use, not a core control function, thus reducing the requirements on the roll gap meter, the roll gap meter arrhythmia, the artificial pressure under control, the system can also work, will not cause the waste of products.
High reliability, because the main control part is a digital pulse on, digital hydraulic cylinder has high anti-interference and high ability of anti pollution, original servo system of double closed loop (pressure and position closed-loop) into pressure single loop.
