The development of the first strip thickness gauge worldwide, that could measure the thickness of the strip during the rolling process in cold mills with an accuracy of µm, was the start of our company in 1963.
Vollmer America
VIP 08 Flatness Measurement System
While the strip thickness tolerances were a significant criterion for the quality assessment of strip material in the eighties and nineties, significant improvements in controls and automation have made good thickness control a given among suppliers.
Today, due to ever increasing requirements, a significant quality criterion to distinguish excellent from adequate suppliers is strip flatness. It is no longer sufficient that the strip flatness be measured and controlled in one of the cold rolling mills in the process chain. The strip flatness must also be kept in view in the following stages of strip processing, which is logical since any thermal strip treatment and any winding and unwinding may change the strip flatness again.
This is where VIP 08 optical shape meter has its application. The target process is not the cold mill but the pickling line, the winding line, the cut-to length line, the levelling line or the coating line. The VIP 08 may also be installed successfully at the hot rolling mill.
If the line, in which the measurement takes place, also has control elements for the flatness control (saddle adjustment, cooling, roll bending or others), VIP 08 may be combined with the proven Vollmer flatness control or also with other flatness control systems.
VIP 08 has also been applied for the flatness measurement of plate material.
Design:
The main components are the light source, the CCD camera and the evaluation unit.
The light source is installed on one side (on the drive side, for example), suspended above the material and the camera on the other side of the material. The system can be designed so that the space directly over the strip is entirely free.
See Figure 1.
Figure 1 – Arrangement of lamp and video camera on-line
The light source creates an approximately 80 mm wide light pattern on the strip material over the entire material width. This light pattern is viewed by the camera.
Particularly attractive is that a free space of only 200 mm is necessary in strip direction. VIP 08 can detect material widths of up to 3000 mm.
Supplementary features for hot mill applications are cooling units and more substantial protection designed into the frame.
Evaluation:
The matrix image, taken by the camera, is read into the industrial PC via a video interface. This system is for processes the video data mathematically to create 200 lines of shape measurements in I-units.
In the next step, these standardized flatness values are processed for visualization and storage. These steps are presently done on 2 processor systems that are connected via TCP/IP.
The standard signal transmission to the line, to a flatness control, to level 2 communication, etc. can be via a TCP/IP network, Profibus DP or discrete digital and analog input and output signals as needed by the application.
Figure 2 – System Overview Screen
Visualization:
The visualization on an industrial monitor (with keyboard and mouse or trackball) in the customer´s control panel typically shows the current flatness in I-Units (1 I-Unit = 10 μm/m). The flatness measurement over the length of the material is shown in the lower part of the main visualization screen in a so-called “carpet” graph.
Stored recordings of measured strips can be played as a video. Both the strip and the line data and the control commands of the control modes are shown. Extensive diagnostic functions are available. Network printer or office workstations are optionally available, can be connected as needed.
Figure 3 – Visualization Example
Measurement Method:
The video signal of the CCD camera shows the light reflection on the material surface.
Camera image 1 shows a relatively flat strip section. Image 2 shows a clear distortion of the light reflection. An image is evaluated every 20 ms and read out in lines.
While comparable optical systems detect height differences of the measurement object per the triangulation process, VIP 08 scans the inclination angles of the material surface elements cyclically.
This measurement method requires moving material. With unflat material, there are different material flow rates over the strip width, due to the relative strip length differences in the material. As long as the material is not cut (in a cut-to-length line, for example), they are shown as very small inclination angle differences in the material surface. These angle differences are used by VIP 08 for the flatness measurement. The measured angles of the strip sections, adjoining over the strip width and not overlapping, form the basis for the determination of the flatness.
A parallel height difference due to vibrations will cause no impairment of the measured parameters (angles). The method is based on the measurement of the angle between the intersection lines, the tangent toward the strip surface on the measurement point in relation to the reference elements. A sufficiently long strip section, including a minimum of 2.5 wave lengths, must be recorded for the determination of the forming indices, ensuring that the resulting measurements will achieve the required accuracy.
Up to 250 measurement points are available for the maximum strip width, resulting in a resolution of about 4 mm with a 1m wide strip (measurement zone width). This high resolution is of particular advantage for the view within the strip edges.
Figure 5 – 3D Display of Strip Sample
The measured inclination angles of the surface elements in relation to the area in strip direction are smaller under strip tension than in tensionless condition. Due to the high sensitivity, even smallest amount of unflatness can be measured and defined realistically by including strip and machine parameters (e.g. the actual total strip tension, E-module, strip thickness, …).
Due to the high sensitivity, VIP 08 can measure extremely small levels of unflatness. Strip, considered as an absolutely flat surface by the human eye, shows a regular longitudinal structure within a range of 0.1 – 0.2 I-units when looking closer at the following example using VIP 08. The resolution of the symmetrical axial flatness error is in line with the distribution of the cooling spray nozzles in the case below:
Figure 6 – Example of VIP 08 Flatness Measurement
Comparative Measurements:
Experienced users know various alternative technologies to measure the strip flatness within the process, such as shapemeter rolls (various principles), laser triangulation processes and light section technologies.
In order to verify the new VIP 08 process of the optical surface inclination angle evaluation, VIP 08 has been installed in various lines parallel to tested and approved shapemeter systems. Test installations in stretch-bend-level lines, pickling line and hot rolling mill have been run. Measurements in comparison to the BFI roll, the laser triangulation system and a segmented measurement roll that has been developed exclusively for application in stretch-bend-level lines have all proven to be consistent.
Example #1 – Comparison with Shape Roll
Figure 7 – Comparison with shape roll on-line (snapshot)
Y Axis = I-Units
Red Graph = VIP 08
X Axis = Strip Width
Blue Graph = Shape Roll
Results shown over the length of the coil:
Figure 8 – Comparison with shape roll over the entire strip length
The recordings show the on-line parallel measurement of a shape roll and the VIP 08 installed beside. Since the shape roll had 40 measurement zones, the VIP 08 measurement values have also been compressed to 40 measurement zones for better comparison.
Example #2 – Comparison with Laser Based Shape Measurement
Figure 9 – Comparison with laser measurement over the entire strip length
As in test case 1, figure 8, this graphic illustrates the flatness measurement over the entire strip. The colors represent the magnitude of the flatness error. The horizontal axis is across the width of the strip and the vertical axis corresponds to the coil length. The color ranges of the I-unit error are identical for both charts.
Since the laser measurement system was limited to 11 traces, the VIP 08 measurement values have also been compressed to 11 measurement traces.
Example #3 – Comparison with Vollmer Shape Roll
This final example is from a continuous SBL process line. In this case, the line is used to flatten strip that has already been rolled to final gauge. The process puts the material under high tension and with a roller leveler section, removes the stress differential that creates the unflatness. The gauge is mounted in the coiling section of the line in which the tension has been reduced. The measurement in this case has been compared to a Vollmer segmented roller with strain gauges to measure the relative tension from which the flatness error is calculated. In this case, it was possible to create both readings on the same graphical display. The upper view shows the current values of the shape (two measurement curves: blue = VIP08, yellow = segmented roller) and the lower view shows the flatness results over the length of the coil. With a strip width of almost 400 mm, the segmented roller is limited to 7 measurement zones. The VIP 08 measurement values have accordingly been compressed to 7 measurement traces.
Figure 10 – Comparison with Vollmer Shape Roll
Shape Control Systems:
An automatic control of the strip flatness is not possible in many lines because of missing control elements. The flatness measurement will then be used to draw conclusions for the optimum setting of upstream processes or to increase the productivity of a line or to avoid damage. It may also be used to provide a report of the flatness of the material for the purchasers of the material.
If the line in which the flatness is measured has control elements to affect the flatness, then automatic strip flatness controls will then be applied, optimizing the strip flatness with a feedback control loop.
By means of a regression analysis, the measured flatness is divided per the existing functions of the machine control elements. Among others, the following control elements have need used with the Vollmer Shape Control System.
# Tilt Control (Error of the 1. order)
# Bending Control (Error of the 2. order)
# Saddle Adjustment (Error of the n-th order)
# Cooling Control (Error of the n-th order)
# Axial Adjustment (Error of the n-th order)
Technical Data:
Applications:
Stretch-bend-level lines, hot and cold mills, pickling lines, trimming lines and many more, form measurement of plates, sheets resp.
Material:
Steel, copper, brass, bronze, aluminum, special alloys, coatings of 0 to 70 N/mm• specific strip tension
For „exotic“ surfaces (we take the liberty of calling surfaces exotic that have not been tested by VIP 08 or Vollmer yet) samples of up to 2000 mm length and 1500 mm width can be sent to Vollmer. This is the maximum dimension that can be measured on our inspection bench with VIP 08. The inspection bench is in our main plant in Hagen, Germany. Samples can be measured there upon receipt of an order to countercheck shapemeter systems using VIP 08 or to verify the suitability for the measurement of „exotic“ surfaces using the VIP 08.
Meas. range: 0.1 – 600 I-units
Resolution: 0.01 I-units
Noise level: 0.00005 I-units
Meas. frequency: 50 Hz
Data output: > 0,4 s
Meas. zone width: max. strip width about / 250
Width measurement: +/- 1.5 x meas. zone width
Strip speed: 0.15 – 25 m/s
Strip temperature: up to 1200° C
Required space
(free view on strip: about 200 mm
Overall width
of components: max. 300 mm
Examples of Application:
Figure 12 –Pickling Line
Figure 13 –Hot Rolling Mill
Summary and Conclusion:
VIP 08 is a new measurement technology that installs easily and offers a very competitive price. The service of the unit is simple so that we hope it will find a wide market.
VIP 08 offers competitive systems to existing versions when the line runs with strip tensions up to about 70 N/mm• (10 KPSI).
For us at Vollmer it is a great pleasure to get to know so many new contacts and customers since we introduced VIP 08 on the market in November 2009. After so many years in the business, this system will develop further fields of application for us in addition to our previously established markets in the metals producing field.
February 2010, Andreas Selent
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March 19th, 2010 at 3:30 am
We are going to prepare Proposal of Flatness measurement system for Plate Mill of POSCO.
Would you kindly deliver us the catalog of VIP 08, Quotation and Supply List (if possible) ?