Road Finisher Cascade Control for Subsoil Unevenness
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Solution Overview
Problem
Conventional road finisher leveling systems fail to accurately compensate for unevenness in the subsoil, as they cannot precisely detect the rear edge of the screed or the influence of uneven ground on the front traction point, leading to imprecise leveling and incomplete compensation of subsoil unevenness.
Innovation Solution
A road finisher with a cascade control leveling system that includes an outer control loop for screed height adjustment, an inner control loop for leveling cylinder position control, and a middle control loop that uses a digital terrain model to determine the target leveling cylinder position, allowing for precise compensation of subsoil unevenness by dividing the control system into nested loops to address disturbances at the traction point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-stage leveling system with distance sensor is used, then the device complexity is low, but the leveling precision is insufficient because the sensor cannot accurately detect the screed trailing edge position or the influence of uneven ground on the front drawbar point
Solution Approach 1:
The leveling system is divided into two independent control stages: a guide controller that manages screed height based on distance sensor measurements, and a traction point controller that manages drawbar position based on tilt sensor measurements. Each stage operates with its own control loop, allowing precise detection and compensation of different positional parameters without requiring a single complex system.
Solution Approach 2:
The traction point control loop is nested within the guide wire control structure. The guide controller operates as the outer control loop managing overall screed height, while the traction point controller operates as an inner control loop managing drawbar position. The inner loop's setpoint is determined by the outer loop, creating a hierarchical nested control architecture that improves precision without proportionally increasing complexity.
2Speed
If tilt sensors are used to detect screed inclination, then the responsiveness to subgrade unevenness is improved, but the reliability decreases because tilt sensors are particularly sensitive to substrate unevenness causing false readings
Solution Approach 1:
The system introduces an intermediary calculation process that combines tilt sensor data with distance sensor data and geometric relationships. Rather than directly using tilt sensor readings which are sensitive to substrate unevenness, the system calculates drawbar position through an intermediary mathematical model that filters out false signals while preserving genuine inclination information.
Solution Approach 2:
The system implements feedback control where the measured drawbar position is continuously compared with the target position, and correction signals are generated to compensate for deviations. This feedback mechanism allows the system to distinguish between genuine subgrade unevenness requiring compensation and false sensor readings, improving reliability while maintaining rapid response.
3Ease of manufacture
If the distance sensor is installed on the drawbar between the front drawbar point and the screed body, then the ease of installation is improved, but the measurement precision deteriorates because the sensor position does not accurately represent the screed trailing edge position or front drawbar point influence
Solution Approach 1:
The system replaces direct mechanical measurement at the optimal location with a combination of easier-to-install sensors and mathematical calculation. Instead of installing the distance sensor precisely at the trailing edge, the system uses the conveniently installed sensor combined with tilt sensor data and geometric calculations to determine the actual trailing edge position, substituting mechanical precision with computational accuracy.
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a road paver (1) with a screed (4) for producing a paving layer (2) on a substrate (3) on which the road paver (1) moves in the direction of travel (R) during a paving operation, wherein the road paver (1) comprises a leveling system (10A, 10B) for adjusting the height of the screed (4) to compensate for unevenness (8) in the substrate (3), wherein the leveling system (10A, 10B) has a cascade control (100A, 100B), wherein the cascade control (100A) comprises either a middle control loop (12) between the outer and inner control loops (11, 13), which has a third controller (Czp) configured tobased on a recorded actual value of the pulling point position (zzp) of the pulling point (6) of the screed (4) relative to the predetermined reference (L) and based on the setpoint value of the pulling point position (rzp) determined by the first controller (Cbo), the setpoint value of the leveling cylinder position (rnz) for the second controller (Czp) is determined, or that the cascade control (100B) between the outer and inner control loops (11, 13) has a pulling point control (C'zp) which is configured to determine, based on the setpoint value of the pulling point position (rzp) of the pulling point (6) of the screed (4) determined by the first controller (Cbo) and based on a digital terrain model (DTM) of the subgrade (3) on which the asphalt paver (1) moves to produce the paving layer (2) provided to the pulling point control (C'zp), the setpoint value of the leveling cylinder position (rnz) for the second controller (Cnz) to determine. The invention further relates to a corresponding leveling method.