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Abstract: A high-precision shape detecting system of cold rolling strip is developed to meet industrial application, which mainly consists of the shape detecting roller, the collecting ring, the digital signal processing (DSP) shape signal processing board and the shape control model. Based on the shape detecting principle, the shape detecting roller is designed with a new integral structure for improving the precision of shape detecting and avoiding scratching strip surface. Based on the DSP technology, the DSP shape signal processing circuit board is designed and embedded in the shape detecting system for the reliability and stability of shape signal processing. The shape detecting system was successfully used in Angang 1 250 mm HC 6-high reversible cold rolling mill. The precision of shape detecting is 0.2 I and the shape deviation is controlled within 6 I after the close loop shape control is input. Key words: shape detecting; digital signal processing (DSP) shape signal processing; close loop shape control; cold rolling strip 58157
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1 Introduction The close loop shape control is the most important key technology in cold rolling productions, because the shape (flatness) of cold rolling strip has a significant impact on the quality of follow-up deep-processed products. However, the shape detecting is the core and premise of the close loop shape control [1−4]. In recent years, a variety of structural forms of shape meters and its related mathematical models have been proposed [5−16]. Usually, the shape detecting systems or the shape meters mainly consist of the shape detecting roller, the collecting ring, the AD acquisition card and the shape control model. Affected by temperature, magnetic field, vibration, humidity, corrosion and other severe working conditions, the traditional shape meters are easy to scratch strip surface, or exist signal drift errors and other unexpected problems when used in practical applications. So, the application ranges of the shape meters are very narrow in practical industrial productions, especially for high quality strip. Based on the shape detecting principle and the shape control theory of cold rolling strip [1−4] and the digital signal processing (DSP) technology [17−19], a high-precision shape detecting system is developed to meet actual industrial application. The integral detecting roller was designed in an innovative way. Its key structural parameters are optimized by finite element method (FEM) for improving the shape signal sensitivity and the shape detecting precision, and avoiding scratching strip surface. Meanwhile, the embedded DSP shape signal processing board is developed for realizing fast signal processing and stable remote transmission of original shape signal.
2 Mechanism analysis of shape defects In the rolling process, the strips are easy to appear apparent longitudinal extension and lateral flow. Shape defects of cold rolling strip are due to different longitudinal extensions of each lateral strip element [3]. Suppose that a section of strip with a length of L is pided into a number of strip elements, as shown in Fig. 1. When the strip exists some shape defects after rolled, it indicates that elongations of strip elements are inconsistent. Suppose that the elongation difference ∆L is between two adjacent strip elements. Among them, the elongation of stretched strip element is negative, which results in tensile stress. And the elongation of compressed Fig. 1 Extending process drawing of strip elements strip element is positive, which results in compressive stress. Usually, the shape defects can be pided into the apparent (dominant) shape defects and the potential (hidden) shape defects. Under certain conditions, if the internal stress of strip element is less than the critical point of instability, the strip has no apparent warping even without tension. And if the internal stress is large enough and reaches the critical point, the apparent strip warping will occur, which is called the apparent shape defect. Usually, the shape defects are hidden under the action of large tension in the rolling process, which is difficult to be identified by conventional means. So, industrial shape detecting system is very important for accuratly detecting shape defects of strip, recognizing the shape pattern and significantly improving the strip shape quality [11]. 3 Principle of shape detecting As shown in Fig. 2, in the production process of cold rolling strip, the detecting roller generates the original shape signal and transfers signals to embedded DSP shape signal processing board by the collecting ring. Fig. 2 Diagram of shape detecting system The detecting roller is usually installed in the export position of cold mill, as shown in Fig. 3. Suppose that the strip wrapping angle around the detecting roller is 2θ, bi is the width of the i-th channel, and hi is the corresponding thickness of strip element. When the strip tightly wounds on the surface of the are real-time detected by piezo-magnetic sensors embeded in the detecting roller, as shown in Fig. 4. Fig. 3 Force analysis drawing of detecting roller Fig. 4 Radial force distribution of detecting roller Various radial forces can be converted to tension or residual stress, namely online shape status of cold strips can be obtained [3]. According to the mechanics relations and the geometric conditions, when the radial force Ni of the i-th channel is known, the calculated value i of tension stress is sin2 iiiihbN