According to the different process requirements of different customers, there are various methods for the length measurement system of straight seam steel pipe, mainly are the following types:

1. Raster ruler for length measurement

Measuring the length with a raster ruler is to install two raster rulers of fixed length on the outside of both ends of the straight seam steel pipe. The raster ruler is driven by the pole columns close to both ends of the steel pipe, and the length of the straight seam steel pipe is measured by the interference phenomenon of light.

The length measurement accuracy with a raster ruler is very high. However, the raster ruler is expensive and difficult to maintain, so it is very sensitive to the influence of dust and on-site vibration.

2. Camera for length measurement

Measuring the length with a camera is to realize the measurement of the steel pipe length through image processing. The principle is to install a series of photoelectric switches at equal distances on one section of the conveying roller of the straight seam steel pipe and add a light source and a camera on the other section. When the steel pipe passes through this area, the length of the steel pipe can be determined according to the position of the image captured on the screen by the camera according to the photoelectric switch.

Measuring the length with a camera can realize on-line measurement and obtain length data when the steel pipe passes through the measurement area without interval. But if there is no special light source irradiation, the steel pipe will be interfered by the external light. After using a special light source, due to the high brightness after the chamfer of the steel pipe, the light reflection is very strong, and it is easy to generate reading errors.

3. Encoder for length measurement

Measuring the length with an encoder is to install an encoder on the cylinder and use the cylinder to drive the steel pipe to move on the drum, and install a series of photoelectric switches at equal distances on the other side. When the steel pipe is touched by the photoelectric switch at the end of the cylinder, the stroke of the cylinder can be converted from the recorded encoder reading, so as to calculate the length of the steel pipe.

Measuring the length with an encoder requires lifting the steel pipe when measuring the length. In addition, there are also some errors in the photoelectric switch detection, and sufficient measurement may be required.

4. Improved encoder for length measurement

Improved encoder for length measurement is an indirect measurement method. By measuring the distance between both ends of the steel pipe and their respective reference points, the length of the steel pipe can be indirectly measured. Set a length measurement vehicle at both ends of the steel pipe, with the initial position being zero and the spacing being L. Then move the length of the editor to the walking distance (L2, L3) at one end of each steel pipe, L - L2 - L3, that is, the length of the steel pipe.

The improved encoder for length measurement overcomes the difficulties such as the large volume of the steel pipe, the complex production site environment, and the inability of the measurement institution to cross the lower support of the steel pipe. It is easy to operate, and the measurement accuracy is less than ±10 mm, and the repeatability accuracy is ≤5mm.