Piezoelectric Jetting Dispenser Amplifier and Thermal Compensation
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Solution Overview
Problem
Existing non-contact jetting dispensers using piezoelectric actuators face limitations due to small displacement, heat generation, and reduced life expectancy, making it challenging to reliably and accurately dispense viscous fluids at high frequencies.
Innovation Solution
A jetting dispenser system with a piezoelectric actuator coupled to a mechanical amplifier, featuring a lever mechanism and a flexural portion, which amplifies the displacement and includes a cooling system to manage heat, and uses materials with different thermal expansion coefficients to enhance longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a piezoelectric stack is used as an actuator, then the response speed and accuracy are improved, but the displacement is too small for proper jetting of fluids
Solution Approach 1:
A mechanical amplifier consisting of a lever arm and flexural pivot acts as an intermediary between the piezoelectric stack and the fluid jetting mechanism. The lever arm amplifies the small displacement of the piezoelectric stack (36 microns) to a larger displacement at the jetting point, enabling proper fluid ejection while preserving the fast response characteristics of the piezoelectric actuator.
2Length of moving object
If the piezo stack is placed under tension to increase displacement, then the displacement is improved, but the life expectancy is severely shortened
Solution Approach 1:
Compression springs are positioned to apply a counteracting compressive force on the piezoelectric stack, ensuring it remains under compression or zero load rather than tension during operation. This protective measure prevents the stack from experiencing tensile stresses that would dramatically reduce its operational life, while still allowing the mechanical amplifier to achieve the necessary displacement through lever action.
3Productivity
If the piezoelectric unit operates at high frequency, then the productivity is improved, but heat generation increases affecting the intended stroke
Solution Approach 1:
The patent converts the harmful thermal expansion effect into a beneficial compensation mechanism. Materials with different thermal expansion coefficients are strategically selected for components experiencing temperature changes, such that their differential expansion counteracts the heat-induced displacement errors, maintaining jetting accuracy even at high operating frequencies where significant heat generation occurs.
4Length of moving object
If a mechanical amplifier is added to increase displacement, then the jetting capability is improved, but the device complexity increases
Solution Approach 1:
The actuator system is segmented into distinct functional modules: the piezoelectric stack module, the mechanical amplifier module (lever arm and flexural pivot), and the fluid jetting module. This segmentation allows each component to be optimized independently and facilitates easier assembly, maintenance, and replacement, reducing the practical complexity despite the added functional capability.
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
The system achieves increased displacement and reliability for dispensing viscous fluids, maintaining accuracy and extending the life expectancy of the actuator while managing heat generation effectively.
Implementation Method 1
A property of the piezo stack is that when a voltage is applied the ceramic material will perform a displacement in one direction
Implementation Method 2
the flexural portion flexes when voltage is applied to the piezoelectric unit so as to move the lever to oppose a resilient bias applied by the flexural portion
Implementation Method 3
a pair of springs arranged on opposite sides of the piezoelectric unit and adapted to maintain the piezoelectric unit under compression at all times
Data Source
Figure 1
Figure 2
Figure 2A~2B
AI summary
A jetting dispenser includes an actuator with a piezoelectric unit that lengthens by a first distance in response to an applied voltage, and an amplifier operatively coupled to the piezoelectric unit. The amplifier includes first and second ends and the second end moves through a second distance, larger than the first distance under the applied voltage. First and second springs are positioned on opposite sides of the piezoelectric unit. The springs are coupled to the piezoelectric unit in a manner that maintains the piezoelectric unit under constant compression. A fluid body includes a movable shaft operatively coupled with the second end of the amplifier and includes a fluid bore and an outlet orifice. The movable shaft is moved by the second end of the amplifier under the applied voltage and jets an amount of fluid from the fluid bore through the outlet orifice.