Trunk Stiffness Bending Device

Trunk control and postural habits greatly influence muscle movement in the rest of the body. The purpose of this project is to design an addition to the Twister mechanism device that measures axial muscle tone in an upright test subject.

Problem Definition
Our goal is to upgrade the Twister's mechanical and electrical components and determine how to make the device functional in an Motion Capture Laboratory. A subsystem consisting of a mechanism to detect lateral responses caused by external forces will be added to the existing structure to allow for a more complex data analysis of human axial tone.

Background
Dr. Victor Gurfinkel and Paul Cordo developed the Twister device while at the Department of Neurology at Oregon Health and Science University. It was then donated to Rajal Cohen at the University of Idaho. The Twister measures torsional resistance and muscular responses in standing subjects during the twisting of the body axis. The device can be flexibly configured to study various aspects of tonic control across the neck, trunk, and/or hips. []

Studies have shown that a person's state of mind can influence how they act, move, and react to known and unknown lateral forces. Hunched and arched posture can influence other muscles in the body and can increase the chance of injury. A person with relaxed mood will typically have a relaxed posture, just as a person with a high stress levels will usually have a rigid posture.

Researchers would like to compare data relating mental to physical responsiveness to determine the cause and effect of negative postural habits. These habits can affect the outcome of a bad fall for an elderly person. The leading accidental causes of death for people aged 60 and above are falls; senior citizens that do survive a fall have a 90% chance of a fracture of the hip. The Twister can evaluate their current posture to determine their likelihood of sustaining injury.

Reassembly
The Twister device arrived completely disassembled and without a definitive guide of how to reassemble it. In the long run, this was very beneficial. The team had to quickly learn how the main mechanism worked, how data was being collected from the torque sensors, and how the data was sent to the data acquisition software. Simultaneously, assembling the Twister gave insight into the details of the project requirements. For example, there were a few components not included in the Twister parts package, so a redesign for these components was required.

The headpiece originally attached to the frame via a thick piece of foam to restrict the subject from full rotational motion. A replacement design consists of a universal joint connected to a telescoping tube. This will retain the original design intent while making the component more efficient and easier to replace. The original Twister collected data from torque sensors and translated it into usable data for the Data Acquisition System (DAQ). A computer with Spike Data Analysis software as well as a program to control the DC motors on the Twister turntable was included in the package. After assembling the hardware, we ran and tested both pieces of software with the Twister. When launching both programs for a complete test, a "Missing 1401 Driver" error occurred. This error led to the discovery that the DAQ was not included in the package, and needed to be replaced.

Design - Alternatives and Selection
The main challenge in upgrading the Twister was overcoming the age of the system. The original components, created in 1999-2000, were simply not compatible with the client's technology, so much of the electrical system and software was included in the design phase of the project.

Software for the User Interface
There are several programs available that are capable of creating an executable program. Two considered were Matlab and Microsoft Visual Studio. The original Twister used Visual Studio to create a Windows Form application. There was also a copy of Matlab already on the computer that would eventually run the Twister. However, the Matlab licence was not capable of data analysis. Using a current version of Visual Studio was deemed the best option. This way, the current and original codes can be compared, and any future edits required should be easier to make.

Data Acquisition System and Electrical Hardware
The Twister needed a replacement for its main electrical controller. A decision was made fairly early on to use an Arduino Mega 2560. It has numerous connections, an impressive processor, and has an incredible amount of support through its website and other Arduino users.

The torque sensors that arrived with the Twister are still in operation. They send data via a LEMO connection, so a circuit was designed to convert the LEMO output to the BNC connection that Motion Monitor uses.

Motor Drive
The original motor still functions; however, a newer model was donated to the team, along with its controller. This new version had a different gear ratio, so the rotation mechanism was redesigned to accommodate. It includes a pulley wheel to be used as a tensioner and a potentiometer to constantly monitor the actual position of the table and report it to the Arduino.

Lateral Force Attachment
A string potentiometer was used for tracking subjects movements when lateral forces are applied. Using a string potentiometer connected directly to the user instead of a standard precision potentiometer should prove to be a much more accurate way of tracking lateral movement caused by a sudden force. The main source of error with a standard precision potentiometer was slippage between the pulley and the cord when the weight dropped or the user reacted to the force.

Mobility
The Twister itself is quite tall; around 9 feet, much too tall for the lab it will eventually inhabit. The lab also is used for other experiments, so the Twister must be capable of moving out of the way. The new design consists of steel ball rollers next to extendable padded feet. The feet can be retracted to allow the Twister to roll, or extended when it is in the correct place. In addition, when all of the major components have been successfully added, the steel bars that make up the corners will be shortened.

Detailed Design - Hardware
The following sections outline more details of the Twister's hardware.

Pulley System
A pulley system is used to create a lateral force on the test subject. The system is composed of two pulleys on the left and right sides of the Twister frame. A cable attached to the electromagnet runs on top of the pulley and attaches to the subject standing inside the Twister frame. To cause a lateral perturbation, voltage is cut off from the electromagnet and the magnet releases the weight. The weights are only released from one side of the Twister at a time. To cause a reaction to the left side of the user, the weights are released from the right side of the subject. Steel bars in various sizes are used for the weights in the pulley system. Voltage control is provided by the microcontroller and triggered by the user interface.

The design that Twister is being based off of calls for a weight drop of 7% of total body weight. The example design exposed test subjects to forward and backward forces on their torso, as oppose to side to side forces with the Twister design. For this reason, varied weights are included so the client can choose the desired force on a case by case basis, with a maximum weight of 15 lbs. The maximum weight was decreased for the Twister model in comparison to the example model out of concern for lower back injuries from sudden side-to-side jolts in the test subject. A 24 Volt electromagnet was chosen for the pulley system so it could be powered without any additional circuitry from the 24 Volt power supply used for the rest of the system. The electromagnets are triggered by the user through the microcontroller, the Arduino Mega 2560. A solid state relay was used as an electrical switch between the voltage supply and signal.

Electrical Components
Twister was built in the late 1990's and all software and hardware is original. Technology has come a long way since then, and the electronics are extremely outdated. The electrical system is composed of a series of circuit boxes: a silver box, a blue box, and a black box. The silver box is the main electrical driver for the system. It contains boards for powering the torque sensors and DC motor, a microcontroller board, a signal conversion board, and input/output boards. The two torque sensors and DC motor run on an independent microcontroller. The signals obtained from the individual microcontrollers are sent to a master microcontroller. A 37 pin cable connects the silver box to the blue box. The blue box is used as a housing that splits the the 37 pin cable into each individual pins. The black box takes only the pins being utilized by the system from the 37 pin connector and relays to the encoders, motors, and torque sensors on Twister.

The new system is broken down into 3 subsystems; Interface Control, Motor Control, and Sensory System. The interface control is composed of the computer and microcontroller. The user controls the system through the user interface, installed through an executable to the desktop of the computer. When a user makes a selection on the interface, it communicates with the microcontroller, and commands are sent to the Motor Control and/or Sensory System. The microcontroller receives feedback from a potentiometer mounted on the inside of the turn table and sends data back to the microcontroller to be used for initialization and calibration. In the Sensory System, only the electromagnets need input from the microcontroller. The inputs for the torque sensors and string potentiometers are user movements. A user's movements trigger changes in the voltages in the potentiometer and torque sensor. This data is considered analog data and is relayed to the motion capture system, Motion Monitor. The data must first go through an analog to digital converter, before it can be accepted by Motion Monitor. Once the data is inside the software, it is converted to usable data by a user defined function. This function is specific to each sensory component and converts the voltage changes into movement data. The data is then plotted within Motion Monitor software, and can be compared side by side with movement data picked up by the motion capture system.

Detailed Design - Software
The following sections outline more details of the Twister's hardware.

Graphical User Interface
The Twister application originally operated through a Guided User Interface (GUI), which sent instructions to the circuits that ran the DC motor what procedure, length, and speed to operate at. Data outputted by the torque sensors was converted and sent to a data acquisition box, the CED 1401, and interpreted by data acquisition software a software program named Spike. The CED 1401 DAQ was not included with the system. A newer model was available, but at $5500, it exceeded the budget. To use the same computer tower, a DAQ tool that was compatible with Windows 2000 .NET framework would be required; however, such a device could not be located. Therefore, the decision was made to redesign the user interface, as well as the data acquisition method.

The Twister software was a C# Windows Form Application made using Visual Studio 1999. That version of Visual Studio used a different .NET framework than the current model, so a direct conversion of the software was not possible. Using C# allowed the current version to be compared directly to the original for requirements and procedures.

The GUI needed to provide the user with the same options as in the original in addition to selections for the new lateral motion attachment. It will have two main sections, "Twister Control" and "Lateral Movement." The Twister Control section will be very similar to the original. There will be three selections for type of movement; ramp, staircase, and sweep. Inside these selections, the user can edit the motor speed, turn iteration, turn duration, and a delay, if applicable. The Lateral Movement section will contain the control for the electromagnets that are the heart of the lateral movement design. The user can select 'Right,' 'Left,' or 'Random,' and when they run the program, the electromagnet will switch off, dropping the corresponding weight and pulling the subject.

Data Acquisition
The torque and lateral movement data obtained through the torque sensors and potentiometers, respectively, needed to align with motion capture data obtained with special cameras in real time. This evolved into one of the primary goals of the project, and learning to communicate with the motion capture system, Motion Monitor, became imperative. Motion Monitor also served as a convenient replacement for the missing DAQ. The cameras the system uses send analog data to its own DAQ, which currently has several empty inputs. The sensors employed by the Twister output analog data, and can plug directly into Motion Monitor through its DAQ.

An Arduino Mega 2560 receives the data from the GUI via serial port and controls what operation(s)the system performs. It initializes the system's power, and relays the data obtained by the Lateral Motion Potentiometers and the Twister Motor to Motion Monitor.

Motor Control
There are three separate paths the motor can take, which spin the test subject in different configurations. The first is a simple sweep, moving the platform back and forth. The second is a staircase path. This is similar to the sweep, except the platform will pause for a given amount of time periodically before continuing on. The third is also like the sweep function, but in this case, the platform begins by sweeping out small angles, and ramps up as it continues.

The code to run these modes is executed by the Arduino. The user selects their motor speed, iterations, and min and max angles and presses the "go" button. The User Interface then sends a series of data values representing these choices over the serial port by which the Arduino is connected. The Arduino is constantly listening for incoming data, so when it receives the series it determines which mode the user selected and executes the motor movement function.

Implementation and Testing
We will be providing data and feedback once we have completed the design process.

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