Unified Crane Control Architecture for Sway-Free Positioning
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Solution Overview
Problem
Existing crane control systems face challenges in simultaneously achieving real-time positioning, motion-induced oscillation suppression, and disturbance rejection, often requiring costly and difficult payload sensing, and are limited by the inability of time-optimal control schemes to be implemented in real-time.
Innovation Solution
A unified control architecture combining an input shaping control module, a position feedback control module, and a disturbance rejection feedback control module, which uses multiple control modules to achieve simultaneous real-time positioning, motion-induced oscillation suppression, and disturbance rejection, and includes a methodology for designing input shapers suitable for nonlinear systems with slew rate limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If feedback control is used to precisely position the overhead support unit, then positioning precision is improved, but the control becomes reactive rather than anticipatory and requires costly payload sensing
Solution Approach 1:
The patent applies preliminary action by using input shaping filters that pre-modify control commands before they are executed. The shaped commands are computed in advance based on the desired trajectory and system dynamics, allowing the controller to anticipate and prevent oscillations before they occur, rather than reacting to them after payload sensing detects cable sway.
2Productivity
If time-optimal control schemes are used to obtain swing-free motion, then productivity is improved, but they cannot be implemented in real-time due to precomputation requirements
Solution Approach 1:
The patent segments the control problem by dividing the control command into multiple shaped impulses that are applied sequentially. This segmentation allows the complex time-optimal control to be broken down into computationally simple steps that can be executed in real-time, with each impulse easily calculable from the previous state without requiring full trajectory precomputation.
3Reliability
If feedback control minimizes cable sway in addition to positioning, then both positioning and oscillation control are improved, but accurate payload sensing is required which is costly and difficult
Solution Approach 1:
The patent introduces an intermediary model of the crane system that relates trolley position and velocity to cable angle and payload oscillation. This intermediary dynamic model allows the controller to estimate payload behavior from easily measured trolley parameters, eliminating the need for direct payload sensing while maintaining effective oscillation control through the shaped command filters.
Data Source
AI summary
Disclosed are algorithms for controlling multiple states of a dynamic system, such as controlling positioning and cable sway in cranes. Exemplary apparatus and methods may be implemented using first and second serially coupled feedback loops coupled to a plant and payload that are to be controlled. The first feedback loop comprises a first control module. It generates a filtered actuator command from an error signal derived from a signal representing a desired system state and a feedback signal indicative of the actual system state. The generated signal is operative to position the payload. The second feedback loop comprises a second control module that generates a second actuator command that is operative to cause the plant to have an output of zero, to eliminate disturbance-induced oscillations. Input shaping may be employed in the first loop for eliminating motion-induced oscillations. The first control module is used for precise payload positioning, and the second control module is used to reject disturbance-induced oscillations. A model reference loop may be employed that outputs a modeled response that is an estimate of the response of the plant in the absence of external disturbances, and which may be used to generate a second actuator command for causing the plant to follow the modeled response.