Unmanned driving refers to an intelligent system built with a computer as the center, endowing equipment with the ability to perceive, plan, and automatically control the environment to realize human-like driving. To realize the unmanned driving function of the road roller, the unmanned driving control system must at least take over Walking, steering, and braking functions. Based on this, a simple stand-alone vibratory roller unmanned system architecture is constructed. This architecture can give the roller the ability to perceive the surrounding environment and its own state through the onboard GPS receiver, angular displacement sensor, and ultrasonic radar, combined with information on the construction area and the information of the rolling construction process. Automatically plan the approach trajectory, rolling trajectory, and deviation correction measures, and automatically control the walking, steering, vibration, and obstacle avoidance functions of the road roller, so that the road roller can complete unmanned driving in limited areas and under limited conditions.
1. Regional positioning
When the road roller locates the compaction area, high-precision positioning coordinates (longitude and latitude) of each inflection point in the compaction area are required. The coordinates can be collected by a high-precision handheld GPS locator or by the roller’s own positioning function. Relatively speaking, if the roller’s own positioning function is used for collection, it is necessary to drive the roller to all inflection points before compaction to record the positioning coordinates. Although it can save 1 high-precision handheld GPS locator, but it is more cumbersome to operate.
The positioning hardware adopts the airborne GPS receiver, and it must be combined with the GPS reference station to use the differential GPS technology for positioning. Obviously, regional compaction requires that the rolling overlapping of two adjacent rolling tracks is not less than 12cm. When only using the airborne GPS, the positioning accuracy is at the meter level, which will inevitably lead to non-overlapping of adjacent rolling tracks and cause pressure leakage. GPS technology can make the positioning accuracy accurate to about 2cm, which can fully meet the requirement of overlap.
2. Mobile positioning
Mobile positioning relies entirely on the onboard GPS receiver and no longer uses the IMU. This is because the vibratory rolling speed of the road roller generally does not exceed 5 km.h^-1, which is much lower than the driving speed of the car at 100 km.h ^-1 and the requirements for mobile positioning are much lower than that of the car. Assuming that the GPS positioning frequency is 10 Hz and the rolling speed of the road roller is 5 km.h^-1, the road roller only travels 13.8 cm between the two positionings, that is, every time the road roller travels 13.8 cm, the unmanned driving system can Once the position is controlled (steering wheel angle) calculation, the driving effect under this control frequency can basically meet the requirements of the roller, and there is no need to cooperate with the IMU to increase the positioning frequency. On the other hand, the short-distance transfer speed of the roller is usually set at 10 km.h^-1, and the roller can only be controlled once every 27.6cm when the onboard GPS is used, and the movement accuracy may be slightly insufficient. Considering that the transfer can pass Manual driving or by limiting the unmanned short-distance transfer speed to below 5 km.h^-1. Under limited conditions, a simple stand-alone unmanned system can completely rely on the onboard GPS receiver for mobile positioning.
3. Posture perception
The road roller needs to use the GPS receiver to cooperate with the angular displacement sensor to sense the attitude. Usually, the road roller adopts articulated steering instead of the front wheel steering like a car. The attitude of the road roller includes the attitude of the front frame and the attitude of the rear frame. It is necessary to use the position data obtained by two GPS receivers fixed on the front frame to determine the front frame. position and heading, it is necessary to use the angular displacement sensor arranged on the steering cross shaft or the displacement sensor on the steering cylinder to measure the angle between the front and rear frames, so as to obtain the position of the rear frame, and then obtain the attitude of the whole vehicle.
4. Obstacle perception
Obstacle perception relies entirely on ultrasonic radar. The rolling speed of the road roller is 5km.h^-1, which is far less than the driving speed of a car at 100km.h^-1. According to the standard requirements, the braking distance of the road roller should not exceed 2.17m when the driving speed is 5km.h^-1. The detection distance of the ultrasonic radar can reach 2~4m, and the ultrasonic radar with a detection distance of about 4m can basically meet the obstacle avoidance requirements during the rolling work of the road roller. Relatively speaking, multi-line laser radar is very accurate for space measurement, but the hardware cost is high, and it is not economical to use it on road rollers. Vision-oriented cameras and ultrasonic radar solutions require professional video and image analysis software, which are more suitable for Large-scale products, multi-variety, and small-batch road roller products that cannot reduce costs through apportionment.
5. Planning software
Adopt an “IF-THEN” decision-making system, relying on specific rule programming. Plan the approach track from the current position of the roller to the starting point of rolling in the construction area through entering the site, plan the rolling track from the starting point of rolling in the construction area to the end of rolling through rolling, and integrate the rolling construction process into the rolling In the trajectory, determine the rolling method (static rolling, large vibration or small vibration) of each point on the rolling trajectory line, plan the deviation correction measures when the actual trajectory and the preset trajectory are different through deviation correction, and confirm whether to track the course or preview track heading, etc.
Compared with automobiles, the complexity of the working conditions of road rollers is low. In essence, the rolling construction technology is the rules of rolling. Based on the rules, track rolling is realized in strict accordance with the entry plan, rolling plan, and deviation correction plan, and according to Obstacle avoidance planning execution avoidance can basically meet the requirements of rolling and obstacle avoidance, and the control is simpler. At the same time, the neural network algorithm based on deep learning is extremely dependent on data. The unmanned road roller driving that is still in its infancy has not yet accumulated enough data, and the neural network algorithm is not suitable for road rollers at this stage.
6. Planning the hardware
The industrial computer is adopted, and the bus structure is connected with the controller on the road roller to issue various control commands and take over the functions of walking, steering, vibration, and braking.
In terms of underlying control, indirect control based on planning and tracking is adopted, and the execution hardware receives various control signals issued by the controller, such as moving forward, braking, steering, and vibrating, to realize unmanned driving.
By analyzing the user characteristics and functional control requirements of traditional road rollers, an unmanned road roller stand-alone system architecture is obtained and combined with the characteristics and functions of the road roller itself, the characteristics of the single-machine unmanned system architecture of the road roller are analyzed, and the road roller realizes unmanned driving. Basic requirements for functions: differential GPS technology, angular displacement sensor, ultrasonic radar and “IF-THEN” decision-making system, etc.
7. Execution hardware
The electronically controlled hardware is preferred, in which the walking speed and steering angle need to be adjusted steplessly, and the electronically controlled proportional pump and electronically controlled proportional steering valve are used. There are three options for vibration: no vibration, large vibration, and small vibration. The electronically controlled two-point vibration pump with switching value is selected. There are two ways of braking: deceleration and emergency braking. The deceleration is realized by controlling the displacement of the electronically controlled proportional pump, and the emergency braking is realized by opening and closing the brake.
In terms of other auxiliary controls, the power supply of the whole machine, engine control, etc. all need manual assistance, which is the same as that of the existing road roller. Signal control and running status are not displayed when unmanned driving, and are the same as existing road rollers when manually driving.
When reaching the top of the mountain, there are always several roads to choose from, including driverless driving. Applicable to different working conditions, different unmanned driving solutions can be selected to form different unmanned driving system architectures. The cost of unmanned driving technology solutions is different, and the degree of intelligence is also different. Obviously, more intelligent unmanned road rollers can incorporate auxiliary control into monitoring, such as integrating the power supply of the whole machine and engine control into automatic control to reduce manual intervention and incorporating the operating status of the road roller into monitoring to avoid equipment running with diseases. The vibration, walking, steering, and braking functions of the roller can be further improved. For example, the IMU can be used to improve the mobile positioning accuracy to adapt to the transfer conditions with a driving speed of 5km. Information, making the braking process more stable, thereby reducing the impact of braking on the equipment and making the operation of the equipment safer. More manual operations can be included in the control, such as combining with the cloud map to make the road roller automatically enter the refueling point for refueling or enter the maintenance point for maintenance, and combining the remote control system for the remote control to completely cancel the cab, etc.