Dual-Loop Inkjet Printhead Control for Large Curved Surfaces
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Solution Overview
Problem
Existing inkjet printing devices struggle to achieve the required precision for decorating large, complex surfaces like the outer surfaces of an aircraft, as they lack sufficient accuracy and adaptability to non-planar surfaces with curvature, and existing solutions do not provide the necessary precision and stability for oscillating surfaces.
Innovation Solution
An inkjet printing device with an articulated robot and a nested dual servocontrol loop system, where the second servocontrol loop has a correction frequency at least five times greater than the first, allowing precise control of the printhead's position and trajectory, using sensors and actuators to correct deviations in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a cartesian robot is used for inkjet printing, then high print accuracy is achieved, but the device is limited to flat surfaces of small dimensions
Solution Approach 1:
The patent replaces the cartesian robot mechanical system with an articulated robot system that has 6 rotational axes. This substitution allows the printing device to adapt to complex curved surfaces while maintaining positioning accuracy through software-based trajectory compensation rather than relying on the rigid linear structure of a cartesian robot.
Solution Approach 2:
The articulated robot provides dynamic adaptability through 6 rotational axes, enabling the printing head to follow complex trajectories on curved surfaces. The system dynamically adjusts its position and orientation to match the surface geometry, unlike the static cartesian structure.
2Area of stationary object
If an articulated robot is used to access large complex surfaces, then surface coverage is improved, but trajectory precision deteriorates to +/â0.5 mm
Solution Approach 1:
The patent implements a feedback mechanism where encoders on each rotational axis provide real-time position data to the control unit. The control unit uses this feedback to calculate and compensate for trajectory deviations, ensuring print precision despite the articulated robot's inherent positioning tolerances.
Solution Approach 2:
The system creates a digital model of the desired print trajectory and uses software algorithms to generate corrected movement paths that account for the articulated robot's mechanical characteristics. This virtual copying and correction of trajectories enables precise printing on complex surfaces.
3Manufacturing precision
If masking elements are used for multi-color markings, then clean outlines are achieved, but the process becomes lengthy and tedious
Solution Approach 1:
The patent extracts and eliminates the masking step entirely by using the inkjet printhead's ability to deposit ink selectively dot-by-dot. The non-contact nature of inkjet printing allows direct deposition of multiple colors without physical masks, removing this time-consuming operation from the process.
Solution Approach 2:
The patent replaces the mechanical masking system with a digital control system that directs the inkjet printhead to deposit ink only where needed. Software control replaces physical masks, enabling multi-color printing without the need for repeated masking and unmasking operations.
4Device complexity
If a single servocontrol loop is used, then device complexity is reduced, but precision on oscillating surfaces is insufficient
Solution Approach 1:
The patent segments the control system into two independent servocontrol loops: an outer loop that controls the articulated robot's gross positioning and an inner loop that controls the printhead's fine positioning relative to the surface. This segmentation allows each loop to operate at different frequencies and handle different aspects of positioning, achieving high precision on oscillating surfaces while maintaining manageable system complexity.
Solution Approach 2:
The control architecture implements a nested structure where the inner servocontrol loop is contained within the outer loop framework. The inner loop operates at a higher frequency to correct rapid surface oscillations, while the outer loop handles slower, larger-scale positioning movements. This nested arrangement enables precise control without requiring an excessively complex single-loop system.
Data Source
AI summary
A inkjet printing device including an articulated robot having a free end, a printing module including a first part linked to the free end of the articulated robot and a second part that is movable with respect to the first part and supporting at least one printhead, a first servocontrol loop configured to control the articulated robot, a second servocontrol loop configured to correct, if necessary, the position of the second part with respect to the first part, which has a correction frequency at least five times greater than that of the first servocontrol loop. This solution makes it possible to obtain an inkjet printing device suitable for complex surfaces of large dimensions, that is highly responsive and offers high print quality.