Motivation

We sought out to control the mechanical degrees of freedom for the microscope. On a practical level, the microscope should have (1) adjustable focus, (2) have the ability to sweep over a larger sample. 

Adjustable focus

The microscope uses a fixed objective lens, with a fixed working range and fixed focal length. A biological microscope uses a translational stage mechanism to move the objective lens along the z-axis, which is usually controlled manually using a knob. 

To automate this, we could have a mechanism either for rotating the knob by attaching motors and gears to the microscope body, or for moving the lens along the Z-axis after we detach the lens from the microscope.

For rotating the knob, we will have to carefully access the holding torque and stepper size of the motors, and we to design the aluminium file frame by ourselves. For detaching the lens, we will have to dismantle the microscope, and find a way to install the lens onto a 3D printer’s printer head.

After accessing the difficulty level and complexity of the two requirements, we decided to go for the latter one, i.e. dismantling the microscope and re-installing it on a 3D printer.

Therefore, the focus of the lens is adjusted by its position on Z-axis, which is controlled by a motor.

Sweeping

At higher magnifications (above 40X) not all of the samples will fit into the scope of the eyepiece. Therefore, this necessitates the controlled movement on X and Y-axis of either lens or the base. This design will preserve the ability of sweep through the whole specimen as well, in case we will need such function in future.

To automate the sweeping function, or the X and Y-axis movement of the lens or the stage, we have two designs to go with as well. One, we can use two stepper motors to drive the adjusting knobs on the microscope stage, which will move the specimen around. Two, we can 3D-print a new stage and install it onto the 3D printer, so that it can move along the base of the printer.

For method 1, the major difficulty lies in the fact that the X adjusting knob will be moved when the Y-position is adjusted. The motor will have to move along or use other additional mechanisms. Thus, we have decided to go with method 2, which has the major difficulty lies in stability control and lighting design.

Therefore, the Y-axis movement will be controlled by the base of the 3D printer, which is driven by a motor. The X-axis movement is carried out by the lens, which is controlled by a motor as well.

Stepper Motor

Working Principle

As the movement of the microscope need to be precise in order to obtain clear images, we wanted to use stepper motors instead of normal DC motors. Instead of going on to full rotation, stepper motors divide one rotation into multiple steps, and they can rotate by a single step if being instructed so. 

Research

In the search of suitable stepper motor, we need to consider the following criteria: 1) Power input of the motors need to match the power output of the microcontroller; 2) The step size of the motor should be sufficiently small, so that the controlled movement of microscope is precise and accurate; 3) The holding torque of the motor should be strong enough to drive the adjustment knob or to move the lens around.

After rigorous research, we have found the following types of stepper motor that possible suit our design.

Name	Step Angle (degree)	Holding Torque (N cm)	Voltage (V) / Current (A)	Lead Time (days)
SOYA NEMA 17	1.8	54	10.2 / 1.7	15
17HS3401	1.8	55	3.22 / 1.67	8 – 15
17HS1070-C5X	1.8	26	2 / 1.3	8 – 14
17HS19-2004S1	1.8	59	2.8 / 2.0	8 – 14
17HS19-1684S-PG5 (Geared stepper motor)	0.35	200	– / 1.7	6 – 14

Choice of Motor

In the end, as we have decided to go with the 3D printer method, i.e. we will dismantle and reinstall the microscope onto the 3D printer frame, our final choice of the stepper motor is the Creality 42mm by 34mm stepper motor.

Speculations:

• Stepper angle: 1.8 degree (200 steps per round of rotation)
• Operating voltage /current: 4.83V / 1.5A
• Rated torque: 0.4 Nm. 

Technical Challenges and Solutions

• The controlling system and the motors were new to us, and we simply did not know how to start.
• We have to re-design the 3D printer frame so that the movement of the lens and the stage coincide with the standard practices on the ordinary biology microscope.
• The configurations files of the motherboard of the motors are very long, and we have to learn from the start. We had to ask Tony for some tutorial and guidance for programming.
• The wiring of the 3D printer frame and the motors was not difficult, because we can refer to other printer that have already been assembled in the lab.
• We have to design, prototyping and redesign many times to have all the adapters to install the microscope on this system.