The application of intelligent control technology in construction machinery products

I. Overview of Intelligent Control Technology

Control technology developed after the establishment of the classical control theory mainly based on the frequency domain method in the 1920s. Control technology was first widely applied in industrial production. Driven by the development of space technology, modern control theory mainly based on the state space method emerged in the 1950s, which led to the extensive development of control technology and the creation of more application fields. Since the 1960s, with the development of computer technology, many new methods and technologies have entered the engineering and productization stages, significantly accelerating the pace of industrial technology updates. This has posed new challenges to automatic control technology and provided conditions for its development, promoting the application of intelligent theory in control technology and giving rise to intelligent control technology.

Intelligent control technology is mainly used to solve the control problems of complex systems that are difficult to solve by traditional methods, such as intelligent robot systems, computer integrated manufacturing systems (CIMS), complex industrial process control systems, aerospace control systems, social and economic management systems, transportation systems, communication network systems, environmental protection and energy systems, etc. These complex systems have the following characteristics: ① There is severe uncertainty in the controlled object, the control model is unknown or the structure and parameters of the model vary over a wide range; ② The controlled object has highly nonlinear characteristics; ③ The control task requirements are complex. For instance, in an intelligent robot system, it is required that the system has the ability to plan and make decisions on its own for a complex task, as well as the ability to automatically avoid obstacles and reach the destination.

Intelligent control technology usually functions through intelligent control systems. In simple terms, an intelligent control system refers to a system with intelligent behavior. It can solve complex, random, fuzzy and flexible control problems that are difficult to describe precisely by mathematical methods by using artificial intelligence methods, and has the capabilities of self-learning, self-adaptation and self-organization. Its main objective is to explore a "thinking" mode that is closer to how the human brain processes things. It also studies a kind of mathematical logic that enables machines to "think" based on a small amount of fuzzy information and certain reasoning criteria, just like humans, and can draw relatively accurate or sufficiently similar conclusions and control strategies.

Applying intelligent control technology to construction machinery products has solved the problem that traditional control methods cannot well adapt to variable and complex objects. Intelligent control technology can adjust control strategies to adapt to the complexity and uncertainty of objects. It does not merely rely on mathematical models, but also conducts online reasoning based on knowledge and experience to determine and optimize the best control strategy, so as to maintain the predetermined quality and expected goals of the system in response to certain uncertainties.

The application of intelligent control technology in construction machinery products is very extensive. This article only takes two typical products with different working characteristics, namely crawler hydraulic excavators and double steel wheel vibratory rollers, as examples for discussion.

Ii. Application of Intelligent Control Technology in Typical Products

Construction machinery is classified into two categories based on the requirements of the operation purpose: One category is machinery without operation quality requirements. Its characteristics are that the operation medium is uneven and non-standard, and the operation load varies greatly. The performance indicators required for this type of machinery are power performance (full utilization of power), economy (fuel consumption), and operation productivity. Another category is machinery with requirements for operation quality. Its characteristics are that the working medium is uniform and standardized, and the load generated during the interaction process between the working device and the medium is basically a stable value. For this type of machinery, operation quality requirements are the top priority, followed by power performance, economy and operation productivity. Excavators belong to the former category of machinery, while road rollers belong to the latter category.

1. Control objectives and strategies

Due to the different operation categories of machines, the control objectives and control strategies for machines of different categories are also different. The intelligent control objective of excavators is "energy conservation and environmental protection, and improvement of operation productivity". The goal of the roller is to "improve the quality and efficiency of road surface compaction".

At present, there are mainly two control strategies for excavators: one is "load adaptive control", and the other is "power adaptive control".

Load adaptation control: Under the condition that the output power of the engine is constant, the hydraulic system (load) regulates itself to adapt to (fully absorb and utilize) the power output of the engine, embodying the principle of "distribution according to work".

Power adaptation control: The engine provides power output based on the actual operating conditions, embodying the principle of "distribution as needed".

Excavators that adopt the "load adaptation control" technology generally have several power selection modes, such as maximum power mode, standard power mode and economic power mode. Under each mode, the engine output power is basically constant, and at the same time, the hydraulic pump is also equipped with several constant power curves to match it. Due to the adoption of engine speed sensing control technology (ESS control technology) in the system, when matching, the absorbed power of the pump in each power mode is set to be greater than or equal to the output power of the engine in that mode. This enables the hydraulic system to fully absorb and utilize the power of the engine, reducing energy loss. The power output of the load and the engine can also be coordinated by adjusting the absorbed power of the pump to prevent the engine from stalling.

In actual operation, the operator selects the power mode of the engine based on the working conditions. This control method also requires manual intervention. Once the power mode is improperly selected, it will also cause waste of power.

Excavators adopting the "power adaptive control" technology operate in an automatic control mode, with the engine providing corresponding power output based on the operation requirements and load size. That is to say, the power system can automatically adapt to the needs of the working system and output power to meet the operation requirements without manual intervention. There is no waste of power output, and the power performance and economy are the best. The design concept is to enable the machine to automatically identify different working conditions and then come up with the most favorable solution for construction. The engine and hydraulic system are constantly in a state of self-regulation to achieve the best balance between operational efficiency and fuel consumption.

The intelligent control technology for excavators also includes some measures to further save energy and simplify operation, as well as facilitate maintenance and upkeep, such as automatic idling, automatic acceleration, self-learning, fault diagnosis and remote control, etc.

The control strategy of the intelligent roller is as follows: Based on the set quality goals, the best solution is sought through the detection of the pavement compaction effect and the automatic adjustment of the adaptive control system to achieve the requirements of the operation quality goals.

The control system can, in accordance with the pre-set operation quality target requirements, automatically adjust the compaction operation performance parameters of the machine (the amplitude and frequency of the vibrating wheel and the machine's traveling speed) through continuous detection and analysis comparison, to achieve effective and uniform compaction results. Of course, the accurate detection of the compaction hardness of the layup is particularly important and serves as the starting point and ultimate goal of all intelligent control. The decision-making process for optimal compaction requires consideration of many external conditions, such as ambient temperature, asphalt mixture temperature, and layer thickness, as well as the nonlinearity of asphalt hardness varying with temperature. Therefore, the basis for decision-making must be based on a large accumulation of knowledge and data. The knowledge databases of foreign products usually accumulate decades of rich construction experience and techniques, and the intelligence level of their machines is relatively high.

2. Control method

Any intelligent control system consists of three processes: ① Information collection; ② Information processing and making decisions (thinking and decision-making); ③ Implement the decision.

Excavators identify the load size by detecting the operating parameters of the hydraulic system, such as the control pressure of the pump in the hydraulic system, the oil delivery pressure of the pump, and the working pressure of each mechanism (walking, rotating, boom lifting and boom retraction), etc. Some also detect the displacement of the pilot handle and the system flow rate, etc.

The excavator controller, based on the collected information, inferences the magnitude of the required power and the optimal speed of the engine through fuzzy control theory. The process of implementing the decision is driven by the controller to operate the engine throttle actuator, setting the engine to the ideal speed and output power.

The roller identifies the quality of ground compaction by continuously detecting the vibration acceleration of the vibrating wheel. The vibration generated by the rotating eccentric block inside the vibrating wheel is theoretically a sine curve. When the vibrating wheel vibrates on the ground, the curve is always disturbed. The disturbance is small on soft ground and large on hard ground. By performing a fast Fourier transform on the acceleration of the vibrating wheel of the roller, the data of ground compaction can be calculated.

For instance, the Varicontrol single steel wheel vibratory roller equipped with the new measurement system BTM-E by BOMAG has for the first time achieved the direct measurement of physical variables. The dynamic hardness modulus EVib (Mn/m ²) of the soil can be calculated by using the interaction relationship between the load of the compacted soil by the roller and the soil deformation result. The asphalt manager is developed for double steel wheel rollers. Based on a brand-new asphalt hardness testing method, this system applies a new asphalt hardness calculation model. Asphalt managers can automatically measure and control the compaction performance of road rollers, continuously provide the most optimized compaction parameters, and bring out the best compaction performance of road rollers. Continuously measure the asphalt temperature and incorporate it into the management system. The operator can monitor the changes in asphalt temperature and observe the increase in compaction degree through the display.

The information processing of the roller involves inputting the collected layer compaction information into the database (knowledge base) of the control system, and through analysis, comparison, judgment, and decision-making on adjusting the machine operation parameters (amplitude and frequency of the vibrating wheel and the machine traveling speed).

The key component for the roller to make decisions is the adjustable frequency and amplitude vibrating wheel. The performance of the vibrating wheel directly affects the compaction effect. The structure of the vibration wheel with an automatic frequency and amplitude modulation mechanism is relatively complex and difficult to implement.

3. Typical application examples

The application of intelligent control technology in construction machinery has significantly enhanced the operational quality and production efficiency of products, saved energy, protected the environment, simplified operations, and facilitated daily maintenance and repair. Intelligent control technology has been widely applied in products that have special requirements for operation quality and energy conservation and environmental protection. At present, some major excavator manufacturers abroad all have their own proprietary intelligent control systems, such as:

The engine control system and main pump control system installed on the excavators of Caterpillar Company in the United States can adapt the effective power of the engine to the power of the hydraulic system in the most effective way, enabling the excavators to work efficiently. According to the load condition of the excavator, actively adjust the output power of the main pump to improve fuel consumption. The engine throttle is set with multiple gears to smoothly control the output power of the main pump. When the engine does not require or only needs a very small flow of hydraulic oil, the Engine Speed automatic Control System (AEC) comes into play and automatically reduces the engine speed.

The CX series of "thinking" intelligent excavators from Case Company in the United States are equipped with full-power digital control (FADEC) engines and an original precise hydraulic control system (PCSTM). Through the load sensing system, the intelligent chip controls the working states related to the engine and the hydraulic system, independently judges the working conditions, and independently selects the best power to complete the work. The engine and hydraulic system are always in a state of continuous self-regulation to achieve the best balance between operation efficiency and fuel consumption, so that the machine can perform at its best in various construction applications.

The Kobelco excavator in Japan is equipped with an ITCS automatic control operating system. The computer can automatically monitor the movements of the operating handle, identify the type of operation at this time through fuzzy logic reasoning, and control the operating system. At the same time, it electronically monitors the engine, automatically adjusts the engine speed, and regulates the flow of the hydraulic system. When the load is low, the engine speed is automatically reduced to make the operation more accurate and easier. When the load is heavy, the maximum power of the engine is exerted to improve the operation efficiency. Meanwhile, the latest equipped "visitation information system" can transmit information such as the working position, working status and machine operation of the excavator over long distances. Users can obtain the latest machine operation information via the Internet or text messages on their mobile phones.

From the mid-1980s to the present, five generations of intelligent vibratory rollers have been developed abroad, among which the German company BOMAG holds the most leading position.

BOMAG's first-generation intelligent roller adopted the measurement technology Omegameter for controlling the compaction status. It consists of an acceleration sensor, a BOM electronic unit and an Omega value display table. Since the vibration acceleration of the vibratory roller's vibration wheel varies with the hardness of the soil, the harder the soil, the greater the acceleration of the vibration wheel. Higher soil hardness corresponds to a better compaction state. However, this technology can only be used to control the compaction state, but not the roller itself.

BOMAG's second-generation intelligent roller has launched Terrameter (soil condition meter) for testing, recording and control. Terrameter also utilizes the relationship between the acceleration of the vibration wheel and the hardness of the soil to test the acceleration and generate an Omega value, thereby determining the compaction state of the soil. When further compaction is impossible, Terrameter gives an indication. At the same time, Terrameter can also identify and record the soft points on the ground and the uneven compaction points, as well as provide curves and lists for compaction control. Terrameter consists of two acceleration sensors, one displacement sensor, an Omega watch and a printer. Terrameter was the first to install displacement sensors to control the traveling speed of the roller based on the different compaction conditions of the ground, which endowed the vibratory roller with "intelligence" for the first time.

BOMAG has introduced two new technologies in its third-generation roller, namely TerrameterBTM-E and Varicontrol. All Varicontrol single steel wheel vibratory rollers are equipped with the BTM-E system. The driver can preset five Evib values (45,80,100,120,150 Mn/m ³) as targets. Through the precise and automated adjustment device, effective and uniform compaction can be achieved. For the first time, BTM-E provided a physical quantity for the compaction state, namely the dynamic hardness modulus EVi b (Mn/m ²) of the soil. Unlike the Omega value, the Evib is basically independent of the parameters of the vibratory roller, so changes in the vibration parameters have no impact on the measurement results.

The Vaticontrol system can generate vibrations that can change directions, allowing the vibration direction to be adjusted steplessly in the vertical and horizontal directions according to the density of the material. Since the vibration direction determines the magnitude of the compaction energy transferred to the soil, this system can match the compaction energy with the soil state.

BOMAG's fourth-generation intelligent roller has introduced a new concept, namely the Compaction Management system Compaction Management BCM03. The BCM03 compaction management system is used as an accessory of the BTM-E control system to provide analysis and management of compaction operations.

The EVib (Mn/m2) value generated by BTM-E is displayed to the driver in the form of a chart by BCM03. All the information of BCM03 can be transmitted to a PC and analyzed and processed on windows using the BCMWIN compaction management program. BCM03 has the following four features:

① Electronic prompts for maintenance and upkeep have been realized. When the roller has been working for a certain period of time or a preset technical indicator exceeds the warning value, the display will give a prompt and show the maintenance and upkeep methods.

② Online fault diagnosis has been achieved. When a fault occurs at a certain point on the roller, the display will give a prompt and show the type of fault and the repair method.

③ Communication between the roller and the computer has been achieved, laying the foundation for network diagnosis.

④ Drivers can observe the compaction status of each section of the compacted area relatively intuitively on the display. But driving