The document describes a small animal loading device created by Akash Chauhan and Ruihe Zhang. The device applies a cyclic compressive force of 3N at 1Hz to a mouse's leg for mechanical loading studies. It uses a linear actuator controlled by an Arduino board with a PID control loop to precisely control force and frequency. Testing showed the device could apply loading for 30 minutes with an error of less than 1.12N using PID control, an improvement over initial tests without PID control. Future work may focus on further improving loading accuracy and adding user interfaces.

1. Small Animal Loading Device
----Final Report
By: Akash Chauhan and Ruihe Zhang

2. Introduction
❖ Project Descriptions and Objectives
❖ Background Research
❖ Alternative Design + Final Conceptual Design
❖ Design Components
➢ Mechanical Components
➢ Electrical Components
❖ Programming Logic
❖ Final Testing + Result Analysis + Challenges Encountered
❖ Future Goals and Take Away

3. Project Descriptions and Objectives
❖ Create a prototype for a mouse loading device to conduct in vivo studies
probing the behavior of bone cells under the influence of mechanical loading
❖ Objective:
➢ Device should be able to vertically supply 3N force at frequency of 1 Hz
➢ Device should apply cyclic loading for at least 15 minutes
➢ Device must be portable
➢ Device’s overall cost should be within $1000

4. Background Research
❖ Mouse placed on acetal plastic platform with
leg sticking out from the edge of the platform
placed between the compressional cups
❖ Sphere curvature on the compression cups
➢ Better fit for the mouse’s leg
❖ Linear motion mechanism is needed to
provide compression.
❖ Flexible top platform allows users to adjust
height easily.
B.A.Christiansen, P.V.Bayly, and M.J.Silva, Journal of
Biomedical Engineering, Constrained Tibial Vibration in
Mice: A Method for Studying the Effects of Vibrational
Loading of Bone

5. Background Research
Top Platform
Force Sensor
Upper Compressional Cup
Mouse Leg
Lower Compressional Cup
Motor (Linear Actuator)
Bottom Platform
Basic Orientation:
V.A.Bhatia and K.L.Troy, SEM, A Portable Small-Scale Mechanical Loading and
Testing Device: Validation and Application to a Mouse Tibia Loading Model

6. Alternative Design
❖ Electromechanical Actuator
❖ Scotch Yoke Mechanism

7. Final Conceptual Design
❖ Justification for selecting actuator
design:
➢ Less machining and mechanical
considerations
➢ Better compatibility with electrical
systems and Arduino
➢ Easier to program with built in
potentiometer
➢ Less wearing components (The pin inside
of the scotch yoke acts as a stress
concentrator)

8. Mechanical Components
❖ Top/Bottom Platform and Threaded Rods
➢ Basic Operating Mechanism
■ Use wrench to rotate nuts counterclockwise
to loosen (the top ones) them
■ Use wrench to rotate nuts clockwise to
tighten them and lock the top platform in
place
■ Note: Rotating the lower nuts
counterclockwise would tighten its grip
Top Plate and Threaded Rods
Lower Nuts

9. Mechanical Components
❖ Bracket Assembly
➢ Basic Operating Mechanism
■ Squeeze tweezer between the
space of the mounting bracket to
loosen the bracket
■ Insert the bolt through the holes
and fasten the nuts onto the bolt
to mesh the mounting and top
bracket together
➢ The top bracket assures stability of the
actuator as it moves and prevents
vibration
Bracket Assembly
Mounting Bracket
Tweezer
Top Bracket

10. Mechanical Components
❖ Upper Compressional Cups 3D
Printed
➢ Basic Operating Mechanism
■ Squeeze force sensor through the
small rectangular gap (right above
the sponge)
■ Push a small wire through the
holes on the upper cups to
suspend the mouse’s leg Upper Compression Cup

11. Mechanical Components
❖ Lower Compressional Cups 3D Printed
➢ Basic Operating Mechanism:
■ The sponge on the lower cup will
increase collision time between force
sensor and the leg to reduce the effect
of sudden impact and overshoot
Lower Compression Cup
Sponge

12. Electrical Components: Overall Circuit Description
Loading Control
Position(Frequency) Control
Experiment Data Recording
& Printing

13. Electrical Components: Linear Actuator
❖ Function: Provide compressional force at a
controllable frequency.
❖ Progressive Automations, PA-14P, customized
BLDC linear actuator.
➢ Connected with BLDC motor controller.
➢ 3 inch stroke length
➢ Max loading 150lbs
➢ Max speed 2 inch/second
➢ Installed with an internal potentiometer to detect rod’s
position.
➢ Charger: Operating with 12V and 5A

14. Electrical Components:Arduino
❖ Function: Giving command to linear actuator
and using PID to control both compression
loading and frequency.
❖ Arduino UNO:
➢ Output voltage: 5V
➢ Analog input (6 pins)
➢ Digital & Digital PWM output (14 pins)

15. Electrical Components: Op-Amp Circuit
❖ Function: Amplifying the signal sent from
sensor and sending it to Arduino.
❖ Components in this circuit:
➢ Force Sensor (FlexiForce A201)
➢ Op-Amp Chip (MCP6004)
➢ Three 1kΩ resistors.
➢ One 100kΩ potentiometer.
➢ 3V battery package.

16. Electrical Components: EEPROM Chip
❖ Function: This EEPROM chip circuit is used to
record the experiment data instantaneously
and store them for later use.
❖ Components in this circuit:
➢ 24LC256 EEPROM chip
➢ Arduino

17. Programming Logic
Without PID: With PID:
Constant motor
speed
Changing motor
speed

18. Final Testing and Results Analysis (Without PID)
❖ Loading: Average Absolute Error
without PID for 30s:
➢ 0.62±0.092 V
➢ 3 ± 1.09N
Force (N) vs. TIme (s) without PID Control

19. Final Testing and Results Analysis (Without PID)
❖ Frequency: Number of cycles
within 30 seconds without
PID:
➢ 31 cycles
➢ Inconsistent frequency each time
interval
Oscilloscope Depicting Frequency Change

20. Final Testing and Results Analysis (With PID)
❖ Loading: Average Absolute
Error with PID for 30s:
➢ 0.62 ±0.1V
➢ 3±1.12N
Force (N) vs. TIme (s) using PID Control

21. Final Testing and Results Analysis (With PID)
❖ Frequency: Number of cycles within
30 seconds with PID
➢ 29 cycles
➢ Consistent frequency in each time interval
Oscilloscope Depicting Frequency Change

22. Challenges Encountered and Measures Taken
❖ Excessive force applied by actuator >3N
➢ Added sponges on the top and bottom compressional cups to reduce overshoot
❖ Large gain on Op-amp circuit (High Sensitivity)
➢ Reduced resistance of potentiometer to optimize sensitivity of force sensor
❖ Misalignment between upper and lower compressional cups
➢ Redesigned and 3D printed bottom compressional cups to achieve parallel alignment

23. Future Goals and Take Away
Goals:
❖ Measure the loading error: how much load
exceeds 3N or how much load is required
to meet 3N? How frequently does the error
occur?
❖ Write a protocol of how to use the device.
❖ Wrap up our design, especially the storage
of electrical components.
Take Away:
❖ Increase loading: Easy
➢ Increase linear actuator’s speed
❖ Increase frequency:
➢ Relatively hard
➢ Increase linear actuator’s speed
➢ Decrease the cyclic travelling distance
❖ Improve user interference:
➢ Improve the linear actuator’s fixture.
➢ Improve the upper compressional cups
and the mechanism for leg suspension.
➢ Improve the top platform moving
mechanism.
➢ Improve coding: more comprehensive PID
control loop

24. Final Product