【Abstract】 This article introduces the device developed to measure the overload and unbalanced load of the container and some opinions on the on-line measurement of the overload and unbalanced load of the railway transportation.
【Keywords】 Railway transportation overload and unbalanced load; static container overload and unbalanced load measuring device
Safety is the most important issue in railway transportation. As we all know, the overload of vehicles is an important hidden danger to the safety of freight, especially the transportation of containers. If there is no testing equipment, it is impossible to judge whether the overload and partial load are caused. It is difficult to judge the cause of the accident caused by this. Generally speaking, accidents caused by railway operation mainly come from three aspects: The first is the overload and unbalanced load caused by cargo loading and reinforcement, including deviation from the horizontal centerline of the vehicle, exceeding the allowable center of gravity height, and insufficient reinforcement. Although there are regulations of the Ministry of Railways for the loading and reinforcement of railway cargo, it is difficult to judge whether it meets the requirements in actual operation; the second is the defects of the vehicle itself, such as the out-of-roundness and defects of the wheels, and the last is the track line. Unevenness, excessive vibration, tilting and snaking caused by corners, etc. The railway department has always hoped that there is an effective and simple method to measure the overload and unbalanced load of vehicles, so that the hidden dangers caused by this can be detected beforehand and eliminated.
The measurement of overload and unbalanced load in railway transportation, especially the dynamic measurement of the so-called unbalanced load when the vehicle is running online, is a complicated and difficult problem. In the past and now, this has been discussed, researched and practiced, and relevant departments have also imported corresponding equipment, but they are not ideal.
- Partial load test of container
As far as I know, for the transportation of bulk materials, such as coal, ore, grain, etc., the partial load caused by the materials is not very large. For the transportation of containers, especially the containers that are transshipped overseas, it is not possible to open the container for inspection and adjust the deviation of the center of gravity during the transportation in my country. The hidden danger caused by this is the focus of the measurement of overload and unbalanced load. In order to measure the overload and unbalanced load of the container, both static and dynamic methods should be included.
I used to develop a static measurement container eccentric load detection system for Beijing Dongfang Weite Weighing Equipment System Co., Ltd. at the Research Institute of Tsinghua University in Shenzhen. The measuring device is a weighing method based on the well-known “four-point moment balance principle”, which mainly measures the position of the center of gravity of an object. In order to ensure measurement accuracy, a high-precision digital system is used for weight measurement (signal measurement). In the process of center of gravity measurement, there is another problem that needs to be solved is how to correctly measure and evaluate the accuracy of the system. Many years ago, my teacher from Harbin Institute of Technology and I developed a measuring device to measure the center of gravity of tank vehicles. I was deeply sorry that we could not find a scientific and accurate method to evaluate the accuracy. For this reason, in this development, I came up with what I call the “relative center of gravity displacement measurement method.” The advantage of this method is that the measured data can be compared with theoretical calculations to determine the accuracy of the system. This method is not only theoretically based, but also convenient, fast and accurate. According to the measurement of the container overload and eccentric load detection system developed by us, the measurement accuracy of the lateral center of gravity eccentricity can reach ±2mm. For two containers with different weights (40 feet, 38.5t and 23.6t respectively), the actual measurement was carried out under windy conditions. During the measurement, the header was turned 180° several times, that is, U-turn, lifted and lowered for measurement, statistical measurement The errors are all ±15mm. After analysis, the main source of error is the tolerance of the container positioning ballast and the influence of wind.
The main disadvantage of this device for statically measuring the eccentric load of the container lies in its convenient, fast and accurate measurement method. However, in actual use, the container needs to be hoisted and placed on the weighing platform, and then hoisted on the vehicle or stacked after measurement, which increases the cargo loading process. Therefore, some people install the load cell or tilt measuring device on the spreader of the container to measure the excessive loading of the container, but I think it is feasible to install the sensor on the spreader and use the conventional center of gravity method. However, it is more difficult to obtain high measurement accuracy than with a weighing table on the ground. It is obviously wrong in principle to measure the overload and unbalanced load of the container only by the inclination of the suspended object. The measurement device for container overload and unbalanced load, related to railway transportation safety, if the actual measurement is performed without a scientific, reliable, and tested measurement device, the result may be more serious than the absence of such a device.
- Partial load test of the vehicle
It is more difficult to implement a device for dynamically measuring vehicle overload and unbalanced load. Based on my past experience in the development of railway scales and the inspection of railway scales, I would like to talk about my views on this issue.
- The measuring device should be as close as possible to the running state of the rolling stock. Therefore, it is not suitable to use the commonly used track scales for measuring the weight of vehicles with foundations or foundation pits. The device that should use continuous rails to install strain gauges on the rails or install weighing transmitters directly under the rails is a measuring device that is closer to the running state of the vehicle and can better reflect the eccentric load of the vehicle.
- Develop standards and measurement methods for vehicle overload and unbalanced load. Whether the railway cargo loading rules formulated by the Ministry of Railways can be used as online dynamic standards for vehicle overloads and unbalanced loads, further certification is required, and scientific and specific standards and measurement methods are required to ensure the safety of vehicles. Standards and measurement methods should be approved by the railway department.
- The measurement of overload and unbalanced load, I think, is not based on measuring the weight of the vehicle, but should measure the force of the vehicle on the track at this time. When a conventional track scale measures the weight of a vehicle, the main purpose of sensor signal processing is to filter out the additional force caused by vehicle vibration to obtain the actual weight of the vehicle. In the case of overload and unbalanced load measurement, the main purpose is to measure the force exerted on the track when the vehicle is running, and the additional force of vehicle vibration cannot be filtered out. In particular, it should be pointed out that the lowest vibration frequency when the vehicle is running can be as low as π Hz. Compared with the additional force of high frequency vibration, the vibration amplitude of the low frequency is much larger for the additional force of the same magnitude, and the amplitude of the additional vibration force is much larger. It is inversely proportional to the square of the frequency. For the same force, the lower the frequency, the greater the amplitude. In order to measure the additional vibration force of extremely low frequency, the measurement distance is required to be very long. In foreign countries, to measure the running state of vehicles with a speed of 100km/h, the length of the measurement section of the continuous track is about 11m.
- Our existing device for measuring vehicle overload and unbalanced load is the result of measurement when the vehicle is traveling at a low speed, and the maximum speed is about 30km/h at most. Whether the result obtained in this way can be applied to the normal driving of the vehicle, whether the result of low speed can be guaranteed, and the safety of normal operation needs to be carefully considered.
- Regardless of whether it is a device for static or dynamic measurement of overload and unbalanced load, as far as the current situation is concerned, it cannot measure the height of the center of gravity of the vehicle. However, the height of the center of gravity is very important to the safety of the vehicle. A long time ago, a teacher from Harbin Institute of Technology and I developed a device for measuring the center of gravity of tank vehicles for the Tank Research Institute. Although it can measure the three-dimensional coordinates of the center of gravity, this device is not suitable for measuring containers because the device is complicated and expensive.
The above are some of my knowledge about vehicle over-bias measurement, and I write it out for reference in the hope that it will be of some help to those engaged in this work.