Loaders and forklifts are self-propelled earth-moving machines that are equipped with a boom, a linkage mechanism and a loading bucket in front of the chassis. If the corresponding working device is replaced, it can also carry out bulldozing, lifting, loading and unloading of wood, etc. It is a construction machine with a wide range of uses.
The loader has a heavy weight, a short wheelbase, and is always in a mobile operation state. It is difficult to use a fixed position weighing instrument to weigh the goods it carries, otherwise it will affect the work efficiency. The method of weighing the goods can better solve this problem. Generally speaking, the higher the accuracy of cargo measurement, the better, and the weighing error generally requires about 0.1% to 0.5%. When the loader is loading bulk cargo, the weight of the loaded cargo is calculated by the method of measuring the weight and drawing line at the initial stage. This method has the characteristics of large error, large randomness and inconvenient management. Overloading will cause direct economic losses and overloaded transportation; less loading and under loading will reduce transportation efficiency and damage the interests of customers. At the same time, because the loader has no weighing device, the loading and unloading of materials must rely on the transport of the vehicle or the use of the floor scale, and the loading and unloading efficiency is also high. With the development of logistics loading and unloading industries such as railways, automobiles, ports, and docks, the requirements for loading and loading efficiency, safety and accuracy are getting higher and higher. An advanced loader weighing system is needed to realize the automatic and accurate measurement of goods during the loading process. It is of great significance to strengthen the management of loading operations, prevent overloading and under loading, improve the efficiency and benefits of loading and unloading operations, and ensuring the safety of vehicle transportation has a significant effect
Weighing System Introduction
The working principle of the loader weighing system:
The 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 sensors or transmitters, and the accuracy of signal acquisition is very important to the weighing accuracy of the loader.
Static weighing system
It is often used for the modification of existing loaders or forklifts. Since there is no appropriate weighing equipment on site, and the user needs to measure for trade settlement, in view of the user's demand for modification costs, the static measurement method is usually selected. The composition of static weighing and weighing equipment: 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 features of static weighing:
1) When weighing each time, the position of the weighing bucket is required to be consistent to ensure the accuracy of the weighing, thus affecting the weighing efficiency;
2) The equipment has fewer functions, and many tasks require manual assistance, such as recording, calculation, etc.;
3) It is suitable for short-term workplaces and does not require a large amount of data processing;
4) Low cost, suitable for some self-employed units or small units;
5) There are few parameters involved, and the installation and debugging are more convenient.
Dynamic Weighing System
For the loading measurement of large units such as stations and ports, a dynamic weighing system should be selected to meet the needs of rapid, continuous measurement and large-scale data management. Dynamic weighing equipment mainly includes: pressure sensor (2) + dynamic control instrument (with printing function) + installation accessories.
The main functional characteristics of dynamic weighing equipment:
1) Cumulative loading, weight setting, display and overweight alarm functions;
2) Single bucket weight weighing, accumulation and display functions;
3) The truck model selection or input function, the truck number entry function;
4) Operator, loader number and loading station code input function;
5) Operation time (year, month, day, hour, minute) recording function;
6) Basic job data storage, printing and query functions;
7) Adopt dynamic sampling and fuzzy algorithm to realize dynamic calibration and dynamic weighing, no need to stop the bucket, and 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 converter, the accuracy is higher.
10) Automatic zero setting or manual zero setting can be set.
Scope of application
It is suitable for automatic weighing measurement, overload protection, workload management, etc. of loaders (including forklifts). It can weigh coal or coke, non-ferrous ore, earthwork, granite or marble, sand, gravel bricks, industrial and civil waste, excavation materials and construction additives. Application places: wheel loaders such as mines, stations, ports, docks, factories, freight yards, etc.
Sensor selection
According to the operating characteristics of the loader, the signal acquisition part generally includes three types of load cells, pressure (oil pressure) sensors, and pressure (oil pressure) transmitters. The performance such as interference is better.
The weighing sensor is generally used instead of the pin shaft to achieve the purpose of weighing. This scheme has high requirements on the structural design and installation dimensional accuracy of the sensor, so in actual operation, there are often adverse phenomena such as low accuracy, inconvenient installation and replacement, and even safety accidents, so it has not been popularized and used.
Pressure (oil pressure) sensor, which converts the liquid pressure into the weight of the loading bucket to complete the weighing operation. It is convenient and quick to modify, the measurement accuracy of the equipment is greatly improved compared to the use of the load cell, and the safety performance is guaranteed.
Force (oil pressure) transmitter, the output of the sensor is mV signal, and the small signal is easily disturbed 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 that require relatively high weighing accuracy. The transmitter solves these problems very well. It has strong anti-interference ability and large output signal (generally 4~20mA or 0-10VDC, 0-5VDC), which greatly reduces the requirements for the signal processing part and the display part. The accuracy of the system is also enhanced accordingly.
The following introduces two kinds of pressure sensors and transmitters suitable for loaders or forklift weighing devices:
Sputtered Thin Film Pressure Sensor
This product adopts sputtering film technology and is designed in combination with the characteristics of the loader weighing system. It mainly converts the loader oil pressure into a weight signal by measuring the loader oil pressure.
1) The main features of this product:
a. Small size, light weight, can be installed directly;
b. High precision and good long-term stability;
c. Good anti-vibration, impact and overload capability;
d. Corrosion resistance, high temperature resistance, small temperature drift
Sputtering Thin Film Pressure Transmitter
PPM-241A also collects weight signals by measuring oil pressure, and uses digital circuits to process sensor signals according to the specific requirements of customers.
1. Features of this product:
a. The signal is large and easy to convert.
b. High precision and good stability.
c. Good anti-vibration, impact and overload capability.
d. Strong anti-interference ability.
e. Corrosion resistance, high temperature resistance, small temperature drift
Sputtered Thin Film Pressure Sensor
This product adopts sputtering film technology and is designed in combination with the characteristics of the loader weighing system. It mainly converts the loader oil pressure into a weight signal by measuring the loader oil pressure.
1) The main features of this product:
a. Small size, light weight, can be installed directly;
b. High precision and good long-term stability;
c. Good anti-vibration, impact and overload capability;
d. Corrosion resistance, high temperature resistance, small temperature drift
Sputtering Thin Film Pressure Transmitter
PPM-241A also collects weight signals by measuring oil pressure, and uses digital circuits to process sensor signals according to the specific requirements of customers.
1. Features of this product:
a. The signal is large and easy to convert.
b. High precision and good stability.
c. Good anti-vibration, impact 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, and the temperature of the oil (medium to be measured) in the oil pump will rise after many times of high pressure.
PPM-242L sensor fully considers the temperature factor in the selection of strain gauges, adopts high-temperature strain gauges, and takes corresponding measures during the production process to make the sensor drift as small as possible, <±0.03%FS, when installing Generally, it is installed through a pressure tube. In this way, the temperature and shock that the sensor is subjected to is alleviated, thereby increasing the stability of the device in use.
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 tools such as sealant or raw material tape should be used during installation;
2) The wiring is strictly performed in accordance with the product manual to prevent product damage due to misoperation
3) When calibrating, multi-parameter tests should be carried out for different orientations and angles to ensure that the weighing accuracy of the equipment is consistent in various states;
4) If the space is limited and cannot be installed normally, the method of leading out the pressure pipe should be considered, and then fix it after the debugging is completed.
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