Test Method Research
Notable: We need to test likely ranges of motion for both back and limbs. Would be nice to find a method that would give us results for BOTH, rather than needing two separate methods.
Concept 1: Control- Sara's Method
This method was described by Sara in Validity and Reliability of a system to measure passive tissue characteristics of the lumbar region during trunk lateral bending in people with and people without low back pain. Method consisted of a moveable cradle with two force transducers (Omegadyne, Inc- 2 stainless steel "S" beam load cells with 50 lb capacities). The tester would use the force transducers and steel cables to guide human specimens' backs into a lateral bending motion. The transducers were then utilized to yield a signal via an ADC converter.
This method was used to measure the validity of a visual motion capture system, hence, actual human specimens were used for each test cycle. It is certainly not applicable in our situation.
Concept 2: P10007: Mechanical Spine Test Platform
P10007 is actually developing a mechanical spine test platform for Sara- allowing Sara to calibrate her VICON camera system. Why not kill 2 birds with 1 stone and see if this mechanical spine would qualify for OUR purposes? Granted, we would need to request some time to use it at Nazareth's clinic- and testing would most likely need to be done at Nazareth?
Concept 3: ****
Described in for validating the performance of wearable motion-sensing devices under controlled conditions. PDF can only be accessed from on campus, tried going through Wally several times with no success. This section will be updated shortly.
Abstract looks to describe exactly what we need:
Abstract. This paper presents validation methods for assessing the accuracy and precision of motion-sensing device (i.e. accelerometer) measurements. The main goals of this paper were to assess the accuracy and precision of these measurements against a gold standard, to determine if differences in manufacturing and assembly significantly affected device performance and to determine if measurement differences due to manufacturing and assembly could be corrected by applying certain post-processing techniques to the measurement data during analysis. In this paper, the validation of a posture and activity detector (PAD), a device containing a tri-axial accelerometer, is described. Validation of the PAD devices required the design of two test fixtures: a test fixture to position the device in a known orientation, and a test fixture to rotate the device at known velocities and accelerations. Device measurements were compared to these known orientations and accelerations. Several post-processing techniques were utilized in an attempt to reduce variability in the measurement error among the devices. In conclusion, some of the measurement errors due to the inevitable differences in manufacturing and assembly were significantly improved (p < 0.01) by these post-processing techniques.
Concept 4: Static/Protractor/VICON
Test methods included:
- Static test- holding unit in a fixed orientation while quantifying the amount of drift that occured on three axes after a period of 10 min
- Quasistatic: Attach one sensor to a rotating block affixed to a protractor with a fine arrow indicator. Picture below, details in PDF.
- Dynamic: Completed in a VICON camera room like Sara's- could we do this also? Maybe as a final test for our sensors?
Concept 5: On-The-Body Experimentation
Rather than design a test fixture, the authors of Use Of Multiple Wearable Inertial Sensors in Upper Limb Motion Tracking elected to design motion patterns on white paper. Four healthy male adults (that's us!) were then instructed to slowly move to follow the patterns. A CODA optical tracker (looks to be like Vicon) was also used to test the motion. Overall I doubt this (human tracking) is something we would do- we need good, hard accuracy numbers.
Concept 6: Mechanical/Electrical Accelerometer Test Method
From US Patent 5895858- describes an automatic and integrated mechanical/electrical accelerometer test system. More complex than we need (includes automatic handler subsystem for feeding accelerometers to the test fixture), but still has some good ideas- shaker subsystem for mechanically testing accelerometers, etc. Biggest downfall is it doesn't include angular testing- which we definitely need. Doubt this will be of any use.
Concept 7: Electrical Accelerometer Test Method
From A Novel Method for Test and Calibration of Capacitive Accelerometers with a Fully Electrical Setup. Once again this method appears to be focused on mass assembly testing rather than testing for accuracy. Interesting concept, though, is that this paper postulates that you can measure the accuracy of an accelerometer's sensitivity through electrical simulation.
Concept 8: Validation Using Current Naz. Video Motion Tracking System
Currently Sara uses a Vicon video motion tracking system in her clinic. It uses reflective sensors and multiple cameras to capture certain points on the patients body. Because this system is already in use and is very accurate, it would be easy to test the sensors chosen against the Vicon system. The sensors could be placed on a test subject, and then the reflective dots for the Vicon system could be placed in the same location. Then compare the data collected by the Vicon system to see the difference in what was collected between the two systems. This will also be a good test method because it can cover both limbs and lower back at the same time, killing two birds with one test method. Also because the Vicon system can measure up to 200hz of information, it will help validate a trend line of data collected by our system that is going to collect data at a much lower rate.