Method of measuring the length of steel pipe

　　1. Grating length measurement

　　The basic principle is: two grating rulers with fixed length are set outside the two ends of the steel pipe respectively, and the grating ruler is driven near the two ends of the steel pipe by the rodless cylinder, and the length of the steel pipe is measured by the interference phenomenon of light.

　　It is characterized by high accuracy. However, grating ruler is expensive and difficult to maintain, which is sensitive to dust and site vibration.

　　2. Camera length measurement.

　　Camera length measurement is to measure the length of steel pipe by image processing. Its principle is to install a series of photoelectric switches with equal distance on one section of steel pipe conveying roller table, and add light source and 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 a certain photoelectric switch on the screen through the image captured by the camera.

　　The feature is that it can realize on-line measurement. When the steel pipe passes through the length measurement area, the length data can be obtained without separation. The disadvantages are: if the special light source is not used, the steel pipe will be interfered by the external light, and the reflection of the light is very strong due to the high brightness of the pipe end after chamfering, which is easy to cause reading error.

　　3. Encoder length measurement

　　The principle is to install an encoder at the oil cylinder, use the oil cylinder to push the steel pipe to move on the roller table, and install a series of photoelectric switches with equal distance on the other side. When the steel pipe is pushed by the oil cylinder and the pipe end touches the photoelectric switch, the stroke of the oil cylinder can be converted from the recorded encoder reading, so that the length of the steel pipe can be calculated.

　　The feature is that the steel pipe needs to be raised when measuring the length. In addition, there are some errors in photoelectric switch detection, which may need to be fully measured.

　　4. Length measurement of improved encoder

　　This method is a kind of indirect measurement method, by measuring the distance between the two end faces of the steel pipe and their respective datum points, the length of the steel pipe is indirectly measured. One length measuring trolley is set at both ends of the steel pipe, with the initial position of zero and the spacing of L. Then move the length of the editor to the walking distance (L2, L3) of each steel pipe end. L-l2-l3 is the length of the steel pipe.

　　This kind of measurement method overcomes the difficulties such as the huge volume of steel pipe, the complex production site environment, and the measurement mechanism can not pass through the lower support platform of steel pipe. This method is easy to operate, the measurement accuracy is within ± 10 mm, and the repetition accuracy is ≤ 5 mm.