Table of Contents
Mechanical FixtureThe mechanical fixture was tested to see how accurate and repeatable the movement of each axis was. Using the methods shown on the build, test, and document page, the results shown below were obtained.
The above test results show how each axis of movement responded to requested movements on the user interface. All three of the linear axes performed within the specification of 0.1mm and were very repeatable. The rotational axes of movement did not perform as well, with each having some significant errors. The errors that were found pointed to a few things that may be causing them. First, it was observed that there was some slight play in the servo motor mount on the pitch axis. The other issue that became clear was that the motors themselves did not seem to responding correctly. To further investigate this, testing was done on a spare servo that is identical to the ones used for the pitch and turntable axes. It was found that the servos could not be accurately controlled to 1 deg of motion using the existing motor control equipment. Further development and possibly a different motor selection are some possible solutions to fix this issue.
Tooth PhantomAfter the revision of project scope, the team was able to detect the material boundaries present in the phantom. Two spikes can be seen on the oscilloscope output shown in Figure 1. Conceivably, the first spike represents the gum material and the second spike represents the material behind the gum (either dentin or bone, depending on probe placement).
The tooth phantom was created using materials that could be easily manipulated, creating a simple manufacturing process for the phantoms. Making multiple phantoms encompasses a quick, effortless process. The dimensions of each tooth phantom were well within specifications, as seen in the test results captured in Figure 2 below. Furthermore, the interface between the tooth phantom and the turn table allows for personnel to change the phantoms in a reasonable amount of time (< 10 min) as demonstrated in the test results in Figure 2.
System Fixture ProgramThe motors were tested separately in order to determine their range of motion and the accuracy of control achievable via the Arduino and Labview configuration. The stepper motors were able to achieve the specification of meeting the 0.1mm accuracy. However, the servo motors were not. As shown, the smallest step size control through Labview achieves an approximate 1.74° change. Better accuracy can be achieved through reworking the feedback system of the servo motors.
The test fixture was successfully able to repeatably and consistently obtain data. It was able to move to the same location on three separate test runs and collect sample data that were consistent.
The test fixture was successfully able to programmatically capture and store data for post-run processing. It was also able to determine based on the below graph what material it was composed of as it collected the data and appended it in the final log file.
Future WorkPerform more research regarding the ultrasonic transducer. It is believed that the 10 MHz probe selected for this application does not exhibit a high enough frequency to detect the minute differences between human tissue. Therefore, a higher frequency probe (~30 MHz) should be tested for use. Furthermore, various styles of transducers are available. It is recommended that an immersion probe be tested for use.
Tooth PhantomFuture work required on the phantom includes:
- 1. Performing research on human/pig tissues to better understand their ultrasonic properties. Once the baseline is determined, materials with a stronger resemblance to the tissues can be selected.
- 2. Creating a representative sulcus that can be constructed and measured to an accuracy of 0.1 mm.
Mechanical Test FixtureFuture work required on the mechanical system includes:
- 1. More rigid motor mounting fixture for pitch axis servo.
- 2. Possible redesign of pitch axis subsystem to allow for less holding torque on the servo. A change in materials to lighten things up or an entirely different method of holding the transducer would improve things.
- 3. Design mechanism to lock turntable in place while a test is being completed. If the test is not being conducted orthogonal to the tooth face it can put a torque on the turntable servo which is not good.
- 4. Build some sort of housing for each of the linear POTs or other future positions sensors to clean things up.
ElectricalFuture work required on the electrical system includes:
- 1. Better positioning system for the long axes. The current method using the voltage dividers has resolution limitations due to the nature of the Analog-to Digital Voltage divider present on the Arduino. The motors are incredibly accurate compared to the feedback system.
- 2. Either rework the pitch and yaw axes to put less angular force on the servo motors or replace the servo motors with larger/more powerful servos.
- 3. Replace the quick disconnects with better connectors/cabling harness to better facilitate longevity of system and allow for better accessibility for troubleshooting.
- 4. Improve the signal processing on the collected signals to better determine minute differences.
- 5. Rework feedback loop of servo motors for better, more accurate control. Could use internal pot of the servo fed back to an ADC and then program through Labview. This would also remove the restriction for keeping the Servo 180 degrees since you would be creating the feedback loop already.
Technical Paper, Poster & Closeout Presentation
The poster can be viewed here: Poster.
The closeout presentation can be viewed here: Week 10 Presentation
The pamphlet we handed out at Imagine RIT: Imagine Pamphlet