TableOfContents

Target Outcome

• For use during patellofemoral joint testing, two properly equivalenced and calibrated pressure sensors.

Prerequisites

• An operating Tekscan sensor model number 5051
• An operating Tekscan handle or "dongle" (interface to the sensor).
• Tekscan software loaded on a laptop for use during the testing.
• Access to the gait lab to use the pressure bladder

Infrastructure

For more details see ["Infrastructure/ExperimentationMechanics"].

Prerequisite Protocols

• ["Specifications/Specimens"].
• ["Specifications/SpecimenPreparation"]
• ["Specifications/Registration"]
• ["Specifications/ExperimentationAnatomicalImaging"]

Protocols

Sensel Equivalencing

Primary Conditions

• Equivalent loading on all sensels

Secondary Conditions

N/A

Measurements

• Sensor output in raw format
• A Tekscan defined, sensor specific, equivalencing file

Operating Procedure

1. Acquire Tekscan sensor 5051 (Fig 1a) and Tekscan "dongle" (Fig 1b) for this test (decide on physical location and/or contact). The "dongle" is the harware interface between the sensor and a USB plugin for a computer. Make sure the computer has the latest Tekscan software installed (version ???).
2. After plugging in the hardware to both the sensor and a computer, ensure the sensor is communicating with the Tekscan software. Physically squeeze the sensor to verify in the real time window of the Tekscan software that the sensels respond to the load.
3. The foot pressure bladder hardware in the gait lab (ND1-07 behind the computers) will be used to evenly load the Tekscan sensor (Fig 1c). Check the operating oil in the compressor (Jun-Air) before plugging it in, turning it on and waiting for the tank to pressurize. Once ready, load the sensor on the pull out tray of the pressure bladder (Fig 1d). Place the sensor approximately in the middle of the tray. Slide the tray into the slot while ensuring the sensor does not bind.
4. Once the sensor is loaded, open the valve on top of the pressure bladder to load the sensor (Fig 1d). With the attached manometer (Fig 1d), verify the application of the maximum possible pressure (approximately 87 psi) and record the actual pressure and the sensor serial number.
5. Verify the sensor is loaded in the real time window of the Tekscan software and then perform the "calibration" procedure in the drop down menu. Fill in the appropriate fields and save the calibration file to the repository in the folder structure for the specimen being tested.
6. Close the valve on the pressure bladder and bleed the pressure from the system. Verify the load has been removed from the sensor in the real time window. Apply the sensor-specific calibration file to the sensor. Close the bleed valve.
7. To verify the calibration has been applied, reload the sensor with the pressure bladder. Verify the sensor reads an equivalent pressure across each sensel. If not, verify the calibration file is applied and/or repeat the steps above.
8. Once complete, save the sensor specific calibration file for use during calibration and testing.

ImageLink(https://simtk.org/svn/openknee/doc/img/PressureBladder_Foot.png, width=700, alt=Experimentation Workflow)

Figure 1. Pressure sensor in a joint (a), dongle attached to the sensor (b) and pressure bladder setup for equilibration of the Tekscan sensor (c and d).

Calibration

Primary Conditions

• Application of a known load of approximately 600 N to the sensor. Ideally, the sensor should be loaded using items of similar stiffness and geometry as a patellofemoral joint.

Secondary Conditions

N/A

Measurements

• Sensor output in raw format

Operating Procedure

1. For calibration, the MTS load frame model???? in the basement of the Lerner will be utilized (picture)
2. The Tekscan provided "power law" calibration approach has been shown to the within 2.7% RMS over the tested sensor range

   • Refer to http://www.ncbi.nlm.nih.gov/pubmed/19154074 for a description.

   • A custom approach to calibration is likely more accurate and could be explored if necessary.

-- ["hallorj"] DateTime(2013-11-04T21:58:44Z) An email will be sent to Tekscan to find out the cost for current software as well as sensor pricing. I will also ask about their fixtures for equivalencing (this has proven challenging in the past).

-- ["hallorj"] DateTime(2013-11-11T17:32:36Z) An email was sent to Tekscan. I will update the specifications once we have more information.

Notes