Owls Challenge Team - The OsteoSonic Device

Our device is called the OsteoSonic, in reference to the study of bone through the use of sound.  It is a sonic bone diagnostic tester that applies a dynamic mechanical stimulus to bone to determine its dynamic response.
 
 

Early Concepts

In order to supply a dynamic stimulus to bones (we selected the spine) and measure its response, we decided to build a device that would provide linear vibration, and measure the applied load and the acceleration of the testing site in response to the vibration.  This led to the following basic conceptual schematic:

Here, the spinous process of a vertebral body interfaces with the tip of the device, which is placed immediately adjacent to an accelerometer.  The accelerometer measures the vibration back and forth of the bone directly by measuring its acceleration.  Behind the accelerometer is the driving element, which in this schematic is piezoelectric.  That is followed by a load cell to measure the force applied.  For simplicity, the accelerometer, driver, and load cell are all placed along the same vibratory axis.  The whole apparatus must be encased and shielded mechanostatically, in order to reduce vibration in other directions than desired.
 
 

Prototype Assembly

    In order to provide a 20Hz to 10KHz range of frequencies at nominal power use, two different vibration generators were eventually used: a voice coil electromagnetic shaker for lower frequencies, and a piezoelectric driver for high frequencies.  These elements (illustrated above) are sold as a single unit by the Wilcoxon corporation, which donated a F4/F7 Combined Shaker to our team.  This unit also has a built-in accelerometer and load cell. Note that in the above picture, the F7 element and the accelerometer output port cannot be seen due to the camera angle.

    In order to make this device more portable, we machined a housing for it and married it to the back half of a power drill casing, as illustrated in the rendering below.  The unit was bracketed between two aluminum plates, which were held together by bolts.  The base plate attaches directly to the drill casing.  The drill portion also afforded us on-board controls such as a trigger switch to operate the device, and the direction selector of the power drill was turned into a switch to alternate between the F4 and F7 units during use.

    Furthermore, a teflon tip was added to the drive piston to maintain comfort for the testing subject as well as ensure good contact between the piston and the bone.  A secondary handle was strapped onto the F4 device for better handling of the device.  Lastly, a safety switch was added.  In the unlikely case that the testing subject experiences discomfort, he/she can simply press the button on the safety switch and the device will shut off immediately.
 
 

The Final Prototype

The Support Hardware

    The finalized device shown above is only half of the system.  While the mechanical device shown above applies the frequency sweep and collects the data, a system of electronics modules must provide the dyanimic signal to the shaker system, and the data must be analyzed.  Below is a picture of the support hardware on a rolling cart, from the front and back:

The dynamic stimulus is provided through a function generator program created by National Instruments LabView software on the PC.  This function goes to the rack mounted black units beneath the computer, which are the power amplifier and matching network for the F7 piezo system.  Once the signal is amplified, it goes to the mechanical tester, shown in the bottom drawer of the cart.  The outputs from the sensors on the mechanical tester go into a charge amplifier, which is the small black box on the right side behind the computer.  The data channels then come out of the charge amp and into the data acquisition box (the small silver box behind the power amp).  This interfaces with LabView back on the PC, allowing for the original function, acceleration, and load channels to be monitored and analyzed simultaneously in real time.

LabView performs Fourier Transforms on the incoming data in real time, allowing for generation of a frequency spectrum of the bone.  The resonant frequency should be shown as the highest peak in the spectrum.

For our future work with this device, click here.