How to Automatically and Accurately Dispense a Fixed Amount of Liquid
One of the biggest challenges of our project was automatically dispensing an accurate amount
of liquid into a container. The right amount of liquid constantly needed to be dispensed in a
container in order for the right amount of liquid to be put onto the roller and then onto the plate.
First of all, a mechanical design had to be created that allows controlled liquid flow. For our
project we designed a large reservoir (vat) with a tube at the bottom. The liquid flows out of the
tube into a container using gravity. This makes the system simple and energy efficient, since no
pump is required.
To control the flow, a pneumatic gripper is used to pinch the tube closed. When the gripper is
closed, the tube is completely blocked and no liquid can pass. When the gripper opens, the tube
returns to its original shape and liquid flows through it. The most important requirement of this
design is that the tube can be fully closed without leakage. At the same time, it must open
consistently so that the flow rate remains predictable.
Next up, the system needs to be calibrated. Because the liquid flows using gravity, the amount
dispensed depends on:
• The diameter of the tube
• The height of the liquid in the reservoir
• The time the tube is open
To determine the correct open time, multiple tests were performed. During these tests:
- The pneumatic gripper was opened for a fixed amount of time.
- The dispensed liquid was measured.
- The results were compared with the target amount.
If the measurements did not match consistently, adjustments were made to the design. For
example:
• A narrower tube was installed to reduce the flow rate.
• The reservoir height was stabilized to keep pressure constant.
• The timing values were fine-tuned in the software.
By repeating these tests, a reliable relationship between opening time and dispensed volume
was established.
The final step is controlling the pneumatic gripper using a Python program. The Python program
sends signals to a digital output that controls a solenoid valve. This valve activates or
deactivates the pneumatic gripper.