Application of Doppler Laser Velocimeter Measuring Instrument in Steel Rolling Mills

The Doppler laser velocimeter measuring instrument is an instrument that uses non-contact sensors to measure the speed and length of steel billets. Two intersecting laser beams are emitted to the surface of the slab, causing light interference and forming the Doppler effect. The movement speed of the interference fringes is proportional to the speed of the object passing through the intersection of the two laser beams. By receiving the spectrum and recording the moving speed of the interference fringes, the moving speed of the billet can be accurately determined. The accuracy of laser measurement reaches N+0.02%, and the measurement accuracy reaches ±0.02mm/min when the casting speed is 0.1m/min.

Doppler laser velocimeter is widely used in steel rolling mills. Generally speaking, a laser velocimeter can be installed above, below or both sides of the steel billet. If the instrument is installed above the billet, the heat radiation from the wide surface of the billet will be too strong and the cooling pressure will be high. Once the speedometer is installed and fixed above, it will affect the production of the billet. There is also a problem of heat radiation when the instrument is installed under the steel billet. The falling waste will contaminate the lens, and cleaning the lens will also delay production. The speedometer is installed on the side of the billet, and the lens is installed on a moving and controllable acceleration platform. It can move as the width of the billet changes, thereby avoiding high-temperature radiation, reducing the installation cost of the instrument and reducing the impact on production.

The Doppler laser measurement system has no contact with the billet, so the maintenance rate of the measuring instrument is low and has no impact on the work of the billet. It can measure the length and speed of the slab. The laser measurement system has high measurement sensitivity and solves the problem of inaccurate billet length.


Laser Doppler Velocimeter in Steel mil



Application of Doppler Laser Velocimeter in thickness control of cold rolled strip

In the steel rolling production process, in order to ensure the stable operation of the continuous rolling process and obtain high-quality plates, the metal second volume flow rate between each stand must be equal. According to the equal flow rate per second criterion, the strip speed information needs to be used in the flow rate AGC (automatic thickness control system). However, it is not easy to really control the speed of the rack exit. During the rolling process, due to the existence of forward slip, there is a certain difference between the linear speed of the motor and the linear speed of the strip outlet. Since the forward slip cannot be measured, the linear speed of the strip at the outlet of the frame cannot be accurately measured, so the conventional thickness cannot truly accurately measure flow per second and control it precisely.

In order to obtain constant control of the flow rate per second, it is necessary to obtain accurate strip speed. As a newer speed measurement system, laser speed measurement can accurately measure speed and has been widely used in rolling mills in recent years. The new laser speedometer has a large measurement range and high precision. The speed measurement range is 1.0~12000m/min, the measurement accuracy is ≤±0.05%, the digital sampling period is less than 2mS, and the repeated measurement rate is ≤±0.02%, which can meet the needs of Thickness control needs. Therefore, in cold rolling production, the laser speedometer is an indispensable key piece of equipment for establishing the flow AGC control system.


In addition to being used for pre-calculation of flow per second, the laser speedometer can also be used for dynamic measurement and control of the forward slip coefficient.

For racks that are not equipped with a thickness gauge, according to the control principle of second flow balance, under the premise that the inlet thickness and speed are known, to ensure the thickness of the outlet, it is only necessary to control the outlet speed of the rack. The speed of the stand exit can be calculated from the roller’s linear speed and forward slip. The linear speed of the roll can be obtained through the pulse counter behind the motor, but the forward slip cannot be measured, so accurate second flow calculation cannot be performed. After the rack is equipped with a laser speedometer, the process computer can correct the calculation results of the forward slip based on the actual measured strip linear speed. However, the set value of the process computer is based on the control cycle of seconds, which makes it difficult to meet the dynamic response requirements. Therefore, the outlet linear speed dynamic control function is introduced into the basic automation control to achieve millisecond-level real-time control.

The application of a laser velocimeter in the thickness control system can effectively eliminate the control lag problem caused by the physical position of the thickness gauge, making the model results more accurate, the control response faster, and achieving true second-second flow balance control; After the laser velocimeter participating conventional thickness control, the thickness accuracy can be improved by 0.1% to 0.3% on the same basis; By controlling the speed of each stand, the slipping phenomenon between the rolling mill rolls or between the rolls and the strip can be effectively prevented and discovered; Using the method of speed measurement participating in automatic thickness control can greatly improve the product quality and yield of strips. Therefore, it is widely welcomed in the cold rolled sheet processing industry.

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