Improvement of the Needle-Type Dispenser for Precise Micro-Droplet Dispensation – Gap Measurement Between the Needle Tip and the Target Surface Based on Needle Vibration –

Micro-droplet dispensation is required in current systems or industrial equipments. However, drop-ondemand inkjet technologies are difficult to use in dispensing micro droplets from high-viscosity liquids. Therefore, the needle-type dispenser using a thin needle and a glass capillary has been developed for microdroplet dispensation. When the needle passes through the capillary with a sample liquid, a droplet of the liquid adheres to the needle tip. The micro droplet can be transcribed to the target surface by bringing the needle-tip droplet into contact with the target surface. The needle-type dispenser can dispense sub-pico-liter amounts of droplets from liquids of several hundred Pa?s. When a micro droplet is dispensed, a gap is formed between the needle tip and the target surface. Amounts of droplets are unstable, as the dispensing gaps fluctuate. Therefore, a contact-detection method of the needle-tip droplet and the target surface is proposed. The needle is vibrated by a piezoelectric actuator through a leaf spring in the proposed method. The needle-vibration characteristic is made variable by the differences in conditions between the needle-tip droplet and the target surface. Therefore, contact of the needle-tip droplet with the target surface can be detected by needle-vibration characteristics. Then, the dispensing gap can be kept constant by contact detection for dispensing accurate amounts of droplets.