Application of single chip microcomputer in crane working condition safety monitoring system

Truck cranes are easy to move and convenient, so they are widely used. Although the operation is simple, the working conditions are very complicated. Operators often find it difficult to find potential dangers, and the safety production situation is very severe, especially for truck-mounted mobile cranes, which often have rollover accidents and even casualties.
This paper develops a truck crane safety monitoring system, which monitors and alarms the control characteristic curves of the crane under various working conditions in real time, and has safe operation prompts, including lateral safety prompts, and automatically cuts off overload items in an emergency, thus integrating working condition monitoring, control, alarm, and recording systems. Compared with the imported equipment "torque limiter", this system is fully functional and economical. After nearly 10 years of practical application and improvement, this system can eliminate safety hazards and ensure safe production. It can also be used on other types of cranes by simply modifying and modifying the calculation parameters, and can complete the installation and commissioning of the equipment simply and quickly.
1 Design specifications and functional requirements
The main functions of the crane operating condition and safety monitoring system include:
(1) abnormal operating condition classification warning, automatically measuring the operating condition and calculating the safe working margin, and issuing different sound and light alarm signals when safety is potentially threatened to remind the operator to pay attention to operating safety;
(2) emergency protection control, when the safe working state is seriously threatened, automatically start the emergency control, stop running in the dangerous direction, and can only run in the safe direction;
(3) sensor signal correction and range calibration, according to the interval where the sensor signal is located, take secondary interpolation compensation correction to improve the measurement accuracy, and automatically calibrate the zero point, automatically judge the sensor abnormality, and ensure the safety of the system;
(4) store the operating characteristic parameters of the crane, according to the characteristic curve of the crane under different working conditions, the operating parameters are provided to the monitoring system in real time;
(5) automatically record abnormal conditions.
2 Detection unit and working principle
The schematic diagram of the automobile crane monitoring system is shown in Figure 1. The monitoring device includes pressure sensor, angle sensor, length sensor, wire overwinding sensor, wire overrelease sensor, etc. The monitoring system is required to collect different physical signals respectively and transmit them to the main control computer for analysis and processing. Overwinding and overrelease are automatically triggered and controlled by switch quantity, which will be omitted here.

The pressure sensor indirectly calculates the weight of the hoisted object by detecting the pressure signal p of the upper and lower chambers of the supporting cylinder; the arm length sensor converts the arm length change into the angle change of the sensor's internal measuring element through the pull wire fixed at the end of the arm, so as to measure the actual length l of the arm; the elevation sensor is installed on the arm, and the angle measuring element is driven to rotate by the weight to detect the arm elevation angle β.
According to the above measurements, the actual weight of the hoisted object is calculated as follows:
W=λ×f(p)/l(1)
In formula (1): f(p) is the quadratic nonlinear function of the pressure measurement signal; λ is the quadratic nonlinear function of the angle signal β; l is the boom length measurement signal.
Under a certain design lifting capacity, the arm length and arm angle are mutually constrained. When the boom elevation angle is constant, as the boom length increases, the lifting radius and lifting height also increase, and the lifting weight should be reduced accordingly to prevent rollover accidents. This is shown in formula (1) as W is inversely proportional to l. On the contrary, when the arm length l is constant, as the boom elevation angle β increases, the lifting weight increases. Refer to the operating characteristic curve of a crane in Figure 2. Curve 1 represents the relationship between the lifting weight W and the working arm length l (expressed as "working amplitude" in the figure), which can be expressed approximately by a quadratic curve in sections. This system integrates the various parameters of the operating characteristic quadratic curve in detail and stores them in non-volatile memory for software to call.

The safe working state of the crane is related to W, β and l. It should be noted that the operating characteristics under different working conditions are different. For example, there are different curves in Figure 2, and different cranes are also quite different. Therefore, the calculation complexity is high and needs to be calculated in sections according to the working condition measurement information. In the actual system, according to the measured results of W, β and l, the operating characteristics of the crane are interpolated and approximated by a quadratic function, and the interpolation coefficients under various working conditions are obtained through the operating characteristic table.

In order to ensure work safety, the monitoring system is usually required to calculate the maximum lifting weight Wmax allowed under specific conditions at any time, and prompt W not to exceed Wmax. After a large number of tests, the calculation of Wmax is obtained as follows:

3 Monitoring unit and working principle
The hardware composition of the crane safety monitoring system is shown in Figure 3. The A/D interface samples the signals of various sensors, including angle, boom length, pressure sensor, etc., to obtain the working parameters of the crane. Then, through equations (1) and (2), the actual lifting weight W under the corresponding working conditions and its ratio to Wmax (also known as the load rate) are calculated. The schematic diagram and text prompt information, including the parameters of concern to the operator such as arm length, arm elevation angle, load, etc., are displayed on the LCD module, and a prompt sound is issued for the operator's reference. When the load rate is greater than 90%, a pre-alarm is issued, and when it is greater than 100%, an alarm is issued, and the forced stop control is automatically enabled. At this time, the crane cannot continue to move in the dangerous direction, such as extending the arm, lifting, etc., thereby realizing the measurement and control protection function of the crane, so that the crane's work meets the safety production requirements.

The constants and intermediate results required in the calculation are stored in an external non-volatile storage unit. With the LCD display and keyboard human-machine interface provided by the system, this system can also complete auxiliary functions such as specific parameter setting, calibration and debugging records.
4 Software Design
The software system completes the following functions:
(1) Sensor signal analysis and calculation, mainly completing the calculation of formula (1) and formula (2). The calculation amount is large, and the AT89S52 single-chip microcomputer [1, 2] is used. The operating characteristics of the crane under different working conditions are different. Therefore, it is required to automatically judge the working conditions (front, rear, side, outrigger, jib, etc.) and select the corresponding calculation coefficients and interpolation formulas during the calculation process, and send the calculation results and prompt information to the display module. Figure 4 is a display effect diagram, which includes information such as whether the jib is extended, whether there is overwinding or overrelease, whether the outrigger is working, whether the main arm is located at the side and rear, the system load rate, and whether it is currently safe.
(2) Alarm and emergency protection: In the case of overwinding, overrelease, overweight, sensor abnormality, etc., the system can give real-time sound and light alarms and emergency treatment, and output control signals through the 8255 interface to start the protection relay action.
(3) Liquid crystal display: using an externally purchased 160×128 dot matrix display module with high clarity. Each screen can display 8×10 16×16 dot matrix Chinese characters. This system uses a mixed display of graphics and text, as shown in Figure 4. The Chinese character dot matrix used by the system is pre-stored in the memory [3].

(4) The membrane keyboard uses a 4×4 keyboard matrix, which is easy to integrate on the instrument panel. In addition to inputting 0~9 numbers, it can also input control characters such as +1, -1, CHK, etc., so as to input some parameters used in the system debugging process. The single-chip computer scans the keyboard action through the 8255 interface circuit and makes corresponding processing.
The situation of crane safety production is very severe. The use of intelligent monitoring instruments, which displays working condition prompt information on the LCD display and issues sound and light prompts and alarm information, can fully help operators to carry out safe production and prevent safety accidents caused by improper operation. This system is suitable for the safety monitoring of wheeled cranes, crawler cranes, and tower cranes, and has a high value of promotion and application.
References
[1] Zhang Yigang. New MCS-51 Single Chip Microcomputer Application Design [M], Harbin: Harbin Institute of Technology Press, 2001: 56-98.
[2] Zhou Chunming. Design and production of AT89S51 multi-function remote control [J], Electronic Production, 2007(6): 16-18.
[3] Xie Weicheng, Yang Jiaguo. Principles and applications of single chip microcomputers and C51 programming [M]. Beijing: Tsinghua University Press, 2005: 70-92.