Inkjet Printhead Start Voltage Control via Pre-Charge Ramp
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Solution Overview
Problem
Existing piezoelectric actuating element driver circuits in inkjet printers face challenges in minimizing cost and power dissipation while meeting drive requirements, particularly due to high voltage pass gates and level shifters.
Innovation Solution
A method and apparatus that utilize a common drive waveform with a pre-charge ramp followed by a steeper slope, allowing for adjustable start voltage of actuation pulses through switching circuits, which simplifies trigger circuitry and reduces thermal dissipation by enabling the use of lower voltages and less complex circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage pass gates and level shifters are used to gate cold switch power waveform on to each individual actuating element, then drive requirements are met, but cost and power dissipation increase
Solution Approach 1:
The patent extracts the voltage adjustment function from the traditional high voltage pass gate and level shifter circuitry. By using a pre-charge ramp that sets the start voltage before the main actuation pulse, the system eliminates the need for complex high voltage switching circuitry while still meeting drive requirements. The voltage adjustment is achieved through timing control of the ramp rather than through high voltage pass gates.
Solution Approach 2:
The pre-charge ramp performs preliminary voltage adjustment before the main actuation pulse is applied. By setting the start voltage during the ramp phase, the system prepares the actuating element with the correct voltage level in advance, eliminating the need for complex real-time voltage adjustment circuitry during the actual actuation.
2Reliability
If high voltage pass gates and level shifters are used to gate cold switch power waveform on to each individual actuating element, then drive requirements are met, but device complexity and cost increase
Solution Approach 1:
The patent removes the complex high voltage pass gate and level shifter circuitry from the system. By using a simple pre-charge ramp approach, the voltage adjustment function is achieved without requiring these complex components, thereby reducing device complexity and cost while still meeting drive requirements.
Solution Approach 2:
The system changes the parameter of voltage adjustment from being achieved through complex circuitry (pass gates, level shifters) to being achieved through timing control of a pre-charge ramp. This parameter change fundamentally simplifies the circuitry while maintaining the ability to meet drive requirements.
3Manufacturing precision
If switching during the steeper slope of the drive waveform is used for voltage adjustment, then precision of trimming is achieved, but trigger circuitry becomes more complex and thermally less efficient
Solution Approach 1:
The pre-charge ramp performs voltage adjustment in advance during a gentle slope phase, before the main actuation pulse. This preliminary action allows for precise trimming without requiring complex trigger circuitry during the steep slope phase, as the voltage adjustment is already complete when the main pulse arrives.
Solution Approach 2:
The drive waveform is segmented into two distinct phases: a pre-charge ramp phase for voltage adjustment and a main actuation pulse phase for droplet ejection. This segmentation allows each phase to be optimized independently, with the ramp phase handling precision voltage adjustment using simple circuitry.
4Device complexity
If a pre-charge ramp with gentle slope is used for voltage adjustment, then trigger circuitry becomes simpler, smaller, cheaper and thermally more efficient, but timing precision requirements increase
Solution Approach 1:
The drive waveform is segmented into a pre-charge ramp phase and a main actuation pulse phase. The ramp phase uses gentle slope for simple timing control, while the main pulse provides the precise triggering for droplet ejection. This segmentation allows simple trigger circuitry during the ramp phase while maintaining precision through the structured two-phase approach.
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 reduces power dissipation and costs by allowing for precise voltage adjustments with simpler, smaller, and more efficient circuitry, compatible with large numbers of actuating elements in printers.
Implementation Method 1
Existing piezoelectric ('piezo') cold switch driver ASICs have the limitation of the cost and power dissipation of the high voltage pass gates
Data Source
AI summary
A printhead provides actuation pulses for driving actuating elements from a common drive waveform via respective switching circuits, the waveform having a pre-charge ramp followed by a steeper slope. A start voltage of a leading edge of the actuation pulse is set by opening the switching circuit to decouple the common drive waveform from its actuating element part way along the pre-charge ramp. After the pre-charge ramp the actuating element is coupled again to the common drive waveform, so that the voltage across the actuating element follows the steeper slope to form the leading edge. Adjusting the timing of the decoupling adjusts the start voltage, enables trimming relative to other actuating elements. The gentle slope of the pre-charge ramp enables the precision of timing of switching to be more relaxed, so that trigger circuitry for controlling the switching circuit can be simpler, smaller, cheaper and thermally more efficient.