Jetting Device Control Using Sub-Threshold Pressure Wave Viscosity Monitoring
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Solution Overview
Problem
Existing inkjet printer technologies face challenges in maintaining uniform performance across ejection units due to non-uniform temperature distributions, which affect the viscosity of ink droplets and their ejection characteristics, despite monitoring of sub-threshold pressure waves.
Innovation Solution
A method involving a calibration step at a reference temperature to establish a reference profile of indicators, followed by monitoring and adjusting settings during operation to compensate for temperature-induced changes, ensuring uniform performance by adjusting actuation signal waveforms and potentially using local temperature control elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the jetting device operates continuously, then productivity is improved, but temperature distribution becomes non-uniform causing performance variation across ejection units
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the actuation signal waveform parameters (amplitude, duration, shape) for each ejection unit based on monitored viscosity indicators. This compensates for temperature-induced viscosity variations, maintaining uniform droplet properties across all units during continuous operation.
Solution Approach 2:
The patent implements local quality by applying individualized compensation to each ejection unit based on its specific temperature conditions and viscosity indicator. Each unit receives customized actuation signals tailored to its local state, ensuring uniform performance despite overall temperature gradients in the device.
2Manufacturing precision
If temperature control is applied to maintain viscosity, then droplet uniformity is improved, but device complexity increases due to additional control systems
Solution Approach 1:
The patent employs feedback by continuously monitoring the viscosity indicator from sub-threshold pressure waves and using this information to adjust actuation signals in real-time. This closed-loop control maintains droplet uniformity without requiring complex external temperature control systems.
Solution Approach 2:
The patent applies self-service by using the existing actuators to generate sub-threshold pressure waves for viscosity measurement. The same components that eject droplets also monitor viscosity conditions, eliminating the need for separate sensing systems and reducing overall device complexity.
3Reliability
If actuation signal amplitude is increased to compensate for high viscosity, then droplet ejection reliability is improved, but energy consumption increases
Solution Approach 1:
The patent applies dynamics by making the actuation signal parameters adaptive rather than static. The amplitude, duration, and waveform shape are dynamically adjusted based on real-time viscosity measurements, ensuring reliable droplet ejection while minimizing energy consumption by using only the necessary signal strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures consistent droplet volume and ejection speed across all ejection units by accurately detecting and compensating for temperature variations, thereby improving the uniformity of inkjet performance and maintaining optimal ink viscosity.
Implementation Method 1
actuators in the ejection units, which actuators may for example be constituted by PZT-based piezoelectric transducers
Implementation Method 2
The decay of the sub-threshold pressure waves can approximately be described by an exponential function with a decay time constant that depends on the amount of damping of the wave and therefore depends critically on the viscosity of the ink
Implementation Method 3
the actuators of the various ejection units will dissipate heat in proportion to the respective droplet generation frequency
Data Source
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AI summary
A method of controlling a property of liquid droplets ejected from a jetting device having an array of ejection units each of which comprises: a cavity connected to a nozzle and an actuator associated with the cavity for exciting a pressure wave in the liquid in the cavity, the method comprising: a step of monitoring a sub-threshold pressure wave oscillating in the cavity but having an amplitude not large enough for jetting-out a droplet, a step of deriving an indicator (τ) for the viscosity of the liquid from the behavior of the sub-threshold pressure wave; and a step of adjusting a setting of the jetting device on the basis of the indicator (τ), characterized by the further steps of: a calibration step in which the array of ejection units is kept at a reference temperature and a reference profile (66) is established by deriving said indicator (τ) for a plurality of ejection units; and a monitoring and control step which is performed in an operating state of the jetting device and comprises establishing an operation profile (70) of said indicator (τ) and adjusting said setting on the basis of a difference between the operation profile (70) and the reference profile (66).