Final Design

The final design is composed of six components:

• Nanoliter injector

• Rotation arm

• Micromanipulation stage

• Controller

• Z-axis stage

• Scissor lift

The nanoliter injection pump is the R-480 purchased from RWD Life Science Company. This pump offers a very fine, controlled injection rate ranging from 0.02 - 200 nl/s. Filling, emptying, and injecting is controlled by a touch-screen LCD display away from the pump. It is compatible with a range of tip sizes from companies outside of their network. These options allow our sponsors to change variables in their experiments to obtain a wide range of results with consistent experimental data. 

The rotation arm is designed to allow manual fine-tuning of the capillary tip’s orientation in the petri dish. Large ergonomic cranks (green) allow comfortable and easy rotation, regardless of hand size. A 22.5:1 gear reduction allows larger margins of error without sacrificing extensive orientation accuracy. A collar clamp (white) allows fine radial length adjustments to the pump. Lastly, tightening knobs (black) ensure that the pump does not slip and the arm is locked tight. 

The micromanipulation stage is designed to allow fine and coarse linear XY control of the capillary tip. The stage is controlled via a controller box, which actuates two stepper motors that connect onto ball screws. The motors are equipped with a 27:1 gearbox for higher motor resolution and mechanical advantage. This design used ball screws to reduce friction and stiction during operation. In addition, the design used a rail-bearing system to minimize surface contact and friction.

The electronic component is a sub-component of the micromanipulator that is designed to control the two stepper motors that drive the micromanipulator stage. The main control unit is an Arduino Mega2560 R3 that controls two TMC 2209 drivers for stepper motors. The speed at which the motors rotate can be toggled between two different speeds. The motors can center midway of their movement range through a homing protocol. The TMC library used to driver the stepper motor drivers is available as an Arduino library. 

The scissor lift allows coarse z-axis control to allow the device to gain the same level as the Nikon Eclipse Ti Inverted Microscope stage. The z-axis stage works concurrently with the rotation arm to safely lower the tip into the petri dish without fracturing it. The z-axis stage is able to translate linearly, at 10 um accuracy.

To quantify the effectiveness of the final design, the following hardware results were gathered.

• Coarse and fine travel speed

• Travel range

• Homing duration

• Step size

To obtain the optimal coarse and fine travel speed, the speeds were qualitatively judged while the tip moved under the Nikon Eclipse Ti Inverted Microscope. The optimal speeds the sponsors agreed on is in the video below.

For travel range, the result is the product of the coarse speed and the time required to travel from one end to the other. From this, the travel range for each axis is approximately 4.5 mm.

For homing duration, a stopwatch recorded the time between the start and end of the homing. Using this method, the average homing duration is 38 seconds.

For step size, the result is the quotient of the distance per ball screw revolution divided by the steps of the motor. Using this method, the distance per step of each stepper motor is 0.185 um/step. Because the target step size is 1 um/step, the hardware achieves a factor of safety of 5.41.