Front loading machine and forklifts are self-propelled earth-moving machinery that are hinged on the front of the chassis and consist of a boom, a linkage mechanism, and a loading bucket. They are used for shoveling, transporting, unloading and leveling operations while moving. If the corresponding working device is replaced, it can also be used for bulldozing, lifting, loading and unloading wood, etc. It is a kind of construction machinery with a very wide range of uses.

The loader is self-heavy, the wheelbase is short, and it is always in a state of mobile operation. It is difficult to use a fixed position weighing instrument to weigh the goods it carries, otherwise it will affect the work efficiency. Therefore, look for a way to complete the alignment during the work process. The method of weighing goods can better solve this problem. Generally, the higher the accuracy requirements for the measurement of goods, the better, and the weighing error generally requires about 0.1% to 0.5%. When the loader is loading bulk cargo, the method of measuring specific gravity and drawing a line is used to calculate the weight of the loaded cargo in the initial stage. This method has the characteristics of large error, large randomness, and inconvenient management. More loading will cause direct economic losses and overload transportation; less loading and underloading will reduce transportation efficiency and harm the interests of customers. At the same time, because the loader does not have a weighing device, the loading and unloading of materials must also rely on the transfer of the car or the use of a floor scale, and the loading and unloading efficiency is low and the cost is high. With the development of logistics loading and unloading industries such as railways, automobiles, ports, and docks, the requirements for efficiency, safety and accuracy of loading and unloading are getting higher and higher. An advanced loader weighing system is needed to realize automatic and accurate measurement of goods during the loading process, which is significant for strengthening the management of loading operations, preventing overloads and underloads, improving the efficiency and benefits of loading and unloading operations, and ensuring the safety of vehicle transportation. Effective.

Weighing system introduction

The working principle of the loader weighing system: Loader weighing system is generally divided into two parts, the signal acquisition part and the signal processing and display part. The signal acquisition part is generally realized by a sensor or a transmitter. The accuracy of signal acquisition is very important to the accuracy of the loader's weighing.

Static weighing system

It is often used to modify existing loaders or forklifts. Since there is no proper weighing equipment on site, and users need to measure for trade settlement, in view of the needs of users for the cost of modification, static measurement methods are usually selected. Static weighing equipment composition: pressure sensor (1 or 2, depending on the accuracy requirements) + ordinary weighing display instrument (optional printer if necessary) + installation accessories (pressure pipe or process interface, etc.).

General characteristics of static weighing:

1) When weighing, the position of the weighing bucket is required to be consistent to ensure the accuracy of the weighing, which affects the weighing efficiency;

2) The equipment has fewer functions, and many tasks need manual assistance, such as recording and calculation;

3) It is suitable for short-term workplaces and does not require a large amount of data processing;

4) Low cost, more suitable for some self-employed units or small units;

5) There are few parameters involved, and it is more convenient to install and debug.

Dynamic weighing system

For the loading measurement of large-scale units such as stations and ports, a dynamic weighing system should be selected to meet the needs of fast, continuous measurement and large-scale data management. The dynamic weighing equipment mainly includes: pressure sensor (2 pcs) + dynamic control instrument (with printing function) + installation accessories.

The main features of dynamic weighing equipment:

1) Cumulative loading, weight setting, display and overweight alarm function;

2) Single bucket weight weighing and accumulation, display function;

3) Truck model selection or input function, truck number input function;

4) Operator, loader number and loading station code input function;

5) Recording function of working time (year, month, day, hour, minute);

6) The basic data storage, printing and query functions of the job;

7) Using dynamic sampling and fuzzy algorithm to achieve dynamic calibration and dynamic weighing, without stopping the bucket, automatic weighing during the lifting process;

8) Use the loader power supply for power supply.

9) Using dual hydraulic sensors and high-precision A/D converters, the accuracy is higher.

10) Automatic or manual zero setting can be set.

Scope of application

It is suitable for loaders (including forklifts) automatic weighing measurement, overload protection, workload management, etc. It can weigh coal or coke, non-ferrous ore, earthwork, granite or marble, sand, gravel brick, industrial and civil garbage, excavation materials and construction additives, etc. Application places: wheel loaders in mines, stations, ports, docks, factories, freight yards, etc.

Sensor selection

According to the operating characteristics of the loader, the signal acquisition part generally has three types of load cells, pressure (oil pressure) sensors, and pressure (oil pressure) transmitters. One point that needs to be emphasized is that the sensors are anti-overload, anti-vibration, insulation, and Performance such as interference should be better.

A. Weighing sensor Generally, the sensor is used instead of the pin shaft to achieve the purpose of weighing at the same time. This solution has high requirements on the structural design and installation dimensional accuracy of the sensor, so in actual operations, there are often disadvantages such as low accuracy, inconvenient installation and replacement, and even safety accidents, so it has not been promoted and used.

B. The pressure (oil pressure) sensor completes the weighing operation by converting the liquid pressure into the weight of the loading bucket. It is convenient and quick to modify, the measurement accuracy of the equipment is greatly improved compared with the use of load cells, and the safety performance is guaranteed.

C. Pressure (oil pressure) transmitter, the sensor output is mV signal, and the small signal is easily interfered during transmission and processing, the converted weight is easy to cause errors, and the requirements for the display part are relatively high. It is more difficult to use in systems with higher accuracy requirements. The transmitter solves these problems very well. It has strong anti-interference ability and large output signal (usually 4-20mA or 0-10VDC, 0-5VDC), so that the requirements for signal processing and display are greatly reduced, and weighing The accuracy of the system has also been enhanced accordingly.

The following introduces two pressure sensors and transmitters suitable for loaders or forklift weighing devices:

Sputtering thin film pressure sensor This product adopts sputtering film technology and is designed in combination with the characteristics of the loader's weighing system. It is mainly converted into a weight signal by measuring the loader's oil pressure. The main features of this product:

a. Small size, light weight, can be directly installed in the process;

b. High precision and good long-term stability;

c. Good anti-vibration, shock and overload capability;

d. Corrosion resistance, high temperature resistance, small temperature drift

Sputtering film pressure transmitter PPM-241A also collects weight signals by measuring oil pressure, and uses digital circuits to process sensor signals according to customer specific requirements.

Features of the product:

a. The signal is large and easy to convert.

b. High precision and good stability.

c. Good anti-vibration, shock and overload capability.

d. Strong anti-interference ability.

e. Corrosion resistance, high temperature resistance, small temperature drift

Resistance strain sensor (Commonly known as SMD sensor PPM-242L)

When the loader weighs the cargo, the oil pump connected to the bucket is constantly moving. After the oil (medium to be measured) in the oil pump is subjected to high pressure for many times, the temperature will rise. The PPM-242L sensor is adequate in the selection of strain gauges. Considering the temperature factor, high temperature strain gauges are used, and corresponding measures are taken during the production process to make the temperature drift of the sensor as small as possible, <±0.03%FS, and it is generally installed through a pressure pipe during installation. In this way, the temperature and impact of the sensor are alleviated, thereby increasing the stability of the device.

1) Main features of PPM-242L:

a. High precision and good long-term stability.

b. Good sealing and corrosion resistance.

c. Low cost and high cost performance.

Installation Precautions

1) Thread installation should ensure sealing, and auxiliary equipment such as sealant or raw material tape should be used during installation;

2) Wiring is performed strictly in accordance with the product manual to prevent product damage due to misoperation;

3) During calibration, multi-parameter tests should be conducted for different orientations and angles to ensure that the equipment has the same weighing accuracy under various conditions;

4) If the space is limited and cannot be installed normally, the installation method should be considered to be drawn out by the pressure pipe, and the installation should be fixed after the debugging is completed.