Separable Piezo Actuator for Liquid Droplet Dispensing
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Solution Overview
Problem
Existing non-contact drop-on-demand dispensers for small volumes face challenges in achieving accurate and reliable dispensing of nano and pico litre size droplets due to the high cost and complexity of bonding a piezo element to the dispensing tip, which also limits versatility and increases the risk of contamination.
Innovation Solution
A dispensing apparatus with a separable actuator assembly that uses piezo elements and a friction-fit dispensing tip, allowing for side loading and easy replacement, along with a mechanism for amplifying actuator movement and controlling pressure waves, enables precise and cost-effective dispensing of small droplets without the need for adhesive bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezo element is bonded to the dispensing tip, then droplet ejection is achieved, but manufacturing cost increases and reliability decreases due to bonding voids
Solution Approach 1:
The piezo element is extracted from the bonded configuration and replaced with a contactless acoustic coupling system. An acoustic coupler transmits ultrasonic vibrations from the piezo element through a coupling medium to the dispensing tip without direct bonding, eliminating the reliability issues of bonding voids while reducing manufacturing complexity
Solution Approach 2:
An acoustic coupler and coupling medium are introduced as intermediaries between the piezo element and the dispensing tip. This intermediary system transmits acoustic energy effectively without requiring direct mechanical bonding, resolving the contradiction between reliable droplet ejection and ease of manufacture
2Reliability
If the piezo actuator element is bonded to the tip, then droplet dispensing is achieved, but versatility decreases and contamination risk increases
Solution Approach 1:
The tip is extracted from the bonded assembly and made separable through the acoustic coupling interface. The dispensing tip can be easily removed and replaced while maintaining acoustic coupling through the coupling medium, enabling versatility and contamination prevention without compromising dispensing accuracy
Solution Approach 2:
The system is segmented into separable components: the piezo element, the acoustic coupler, the coupling medium, and the dispensing tip. This segmentation allows the tip to be independently replaced for different applications while maintaining the core actuation system, enhancing versatility and reducing contamination risk
3Strength
If bonding cement is used to attach the piezo element, then mechanical connection is achieved, but performance and repeatability are impaired by bonding voids
Solution Approach 1:
The mechanical bonding system is replaced with an acoustic coupling system. The coupling medium transmits ultrasonic vibrations effectively without requiring mechanical adhesion, eliminating bonding voids and their negative impact on performance repeatability while maintaining sufficient mechanical connection through acoustic impedance matching
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 solution provides improved accuracy, reduced risk of contamination, and lower costs by allowing interchangeable tips, enabling reliable dispensing of small volumes with enhanced versatility and efficiency in biomedical and industrial applications.
Implementation Method 1
bond a piezo element to a tip near the orifice of a dispenser. Because of this bond, the sub-micron vibrations (pressure waves) of the piezo element are transferred to the liquid, causing drops to be ejected from the orifice
Implementation Method 2
the actuator assembly comprises an interface for contacting the dispensing tip and for transferring acoustic energy from the actuator element to the tip
Implementation Method 3
the actuator assembly comprises an inertial mass for the actuator element to act against in order to couple pressure waves into the dispensing tip
Data Source
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AI summary
An apparatus for dispensing droplets comprises a dispensing tip (2, 190, 210) with an orifice (4) having a cross sectional area in the range of 0.00002 mm2 to 0.03 mm2. An actuator assembly (13-15, 50, 80) comprising an actuator element engages with and disengage from the tip and, when engaged, couples acoustic energy to liquid in the tip to expel the liquid through the orifice as a droplet. The actuator assembly includes one or more piezo elements, which may be in the form of piezo stacks. In some embodiments, the actuator assembly comprises a plurality of jaws (51, 52, 61) adapted to move to engage with the dispensing tip for dispensing. This allows side loading of the tip (180) followed by movement of the actuator assembly (153) to engage the tip (180).