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 evaluate the Twister 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
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. [] Postural habits can greatly affect a person's life physically and mentally. Studies have shown that patients with certain postural intentions had corresponding postural alignment traits. A person's state of mind can influence how they act, move, and react to known and unknown lateral forces against them. A hunched and arched posture can influence other muscles in the body and can increase the chances of injuries. A person with relaxed mood will typically have a relaxed posture, as will a person with a high stress levels will usually have a rigid posture. This can be applied generally to any person, regardless of age. 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. 40% of people with falling related injuries will be in chronic pain and will be dependent on medical assistance. Risk factors for falls include ergonomic factors as in falling off a ladder, tripping over a curb, or slipping. Intrinsic factors like age and disease also contribute to an increased risk of falling. Postural instructions, lighten up, relax, and pull, also affect mobility. When a person knows that a force is going to be exerted towards them, their muscles will preemptively tense up creating a reaction that is completely different than an unknown force contacting a person. Comparing data related to mental responsiveness to physical responsiveness will help researchers figure out how and why people fall and the cause of negative postural habits.

Reassembly
We received the Twister device completely disassembled and without a definitive guide of how to reassemble it. This helped us in the long term for learning how the mechanism worked, the way data was being collected from the torque sensors, and the data being sent to the data acquisition software. Assembling Twister from the ground up also helped us evaluate the needs for the project. The headpiece originally attached to the frame by a piece of thick foam to restrict the subject from full rotational motion, was lost in transit to us and we are currently working on a redesign for this. Torque data is sent from the sensors to an electrical box containing circuits that translates the torque signals into usable data for the data acquisition system (DAQ). The translated data is sent to the 1401 data acquisition system, the CED 1401, and shown graphically in real time on Spike analysis package. We received a computer with a license for Spike data analysis as well as a program to control the DC motors on the Twister turntable. After assembling the hardware, we ran and tested both pieces of software with the hardware. The Twister program allows the tester to set initial position, ramp speed, number of stairs, stair size, and stair duration. It also has three different modes, Staircase, Ramps, and Stairs, and a manual or external trigger for starting the system. Modes for the motor dictate how the turntable is spinning. When launching both programs for the test, we received an error, "Missing 1401 Driver". After researching the error, we discovered that the 1401 DAQ was not shipped with the rest of the components.

Software
Twister originally received operating instructions for a program made specifically for the mechanics. The Twister application worked by giving instructions to the electronics to tell the DC motor what procedure, length, and speed to operate at. Data outputted by the torque sensors was delivered by a data acquisition box, the CED 1401, and interpreted by data acquisition software made specifically for the CED 1401; a software program names Spike. The CED 1401 DAQ was not included with the system, and a new model was out of our budget at a cost of $5500. Finding a DAQ tool that was compatible with Windows 2000 .NET framework, so we could use the Twister software, as well as sold in today's market was unsuccessful, and we decided to redesign the front and back end of the user interface, as well as the data acquisition method. The Twister software was a C++ Windows Form Application made with Visual Studio 1999. A different .NET framework was used with that year of Visual Studio, so a direct conversion of the software to a current .NET platform was not possible. A decision was made to use the C# programming language for the new Twister application because of the ability to reference the original Twister program for methods on driving the motor, calibrating the motor, and running the Twister system, and build the new interface on what was already known. A client specification that needed to be met was a connection of the motion capture data with the torque and lateral movement data in real time. One of the primary goals of this project is to integrate the Twister data with data from a motion capture system, Motion Monitor. Through research, we found that Motion Monitor can accept all analog signals and most digital signals; it can also translate those signals into usable data. The torque sensors and string potentiometer produce analog signals and meet the specifications required for data analysis by Motion Monitor. We are currently building a Windows Form that incorporates most of the old features of Spike and new interfacing for the lateral movement attachment. The new program includes selection buttons for initial position, cycle duration, interval length, and mode for the turn table mechanism. A trigger begins communication with the microcontroller, the Arduino Mega 2560, which has an instructional code loaded onto it. A code written to the Arduino Mega 2560 in a Arduino C programming language tells the system exactly what operation(s) to do and for what time interval to do them. Currently, the microcontroller code consist of exact operations a user might want to inhibit on Twister from motor cycle type, to which side of the lateral perturbation attachment to deactivate. The user is indirectly interacting with the microcontroller through the Windows Form application, the user interface. The microcontroller is connected directly to a computer with a defined serial port. The user interface interacts with the same serial port. When a user presses a button to drive a command to the Twister system, the user interface sends a signal to the known serial port and the microcontroller picks up the signal from it. This method is being used for basic testing and we plan on creating a direct link between the Twister system and the user interface, using the microcontroller as an intermediary instead of a system driver.

Pulley System
For the Twister attachment, we are planning on a designing a pulley system that will do the perturbation of the person sideways (left and right). Since we are designing a pulley system we are going to the basics: pulleys, weights, and rope. After looking at various types of pulleys, I came up with three options for the pulley. I found two different designs of pulleys on McMaster Carr and the third option is making a custom pulley ourselves. After I was done searching for pulleys, I looked at the weights and the rope. From what I can find online, calibrated weights are expensive. A single 5 [lb] (2.27 [kg]) weight cost about $65 on McMaster Carr. So I decided that the best option for us is to find/buy chucks of steel ($15 for 2x2x72 [in] bar of steel from McMaster Carr) and cut the steel into the various weight sizes needed. Last thing is the rope, and this was relatively cheap on McMaster Carr, it is only $0.91 for 1 [ft] (30.5 [cm]). I only looked on McMaster Carr, because they have the largest selection of things, and everything that I am buy (the pulley, steel, and rope) are all relatively cheap things to buy, so it doesn’t really matter where these materials are being purchased. Also, prior to looking at McMaster Carr, I went to Moscow Building Supply and Ace Hardware to see if they have any of the need material in stock. I was unable to find the right size of diameter rope, and I could find a proper pulley in these stores (all the pulley the two stores have in stock are hanging pulleys).

Electromagnets
To create a lateral force we will be using a pulley system located on the sides of the Twister mechanism. Electromagnets will be attached to pulley system to create lateral forces on the subject. The design that the side to side perturbation mechanism is being based off of calls for a weight drop of around 7% of total body weight (meaning that for an average 175 lb person the weight needed would be 12 lbs on each pulley). However because the old design was for forward and backward movement it required more force for proper test results. The weight that will be used for the current testing has yet to be determined, but given preliminary calculations it seems reasonable that the weight required will not exceed 15 lbs. Then, given a safety factor of two, the electromagnets should have a holding capacity of roughly 30 lbs. Electromagnets in this range are usually 12 volt DC and require a positive and ground connection.

After initial design considerations, a 24V electromagnet was selected for use with the new Twister addition. These can be powered directly from the 24V power source that came with the original Twister. Because a micro-controller cannot sustain voltages that high, additional hardware will be used to control the activation of the electromagnets. The current conceptual design uses two solid state relays, one for each magnet, both controlled by an Arduino Mega. This way, the user can send a signal to the Arduino via the user interface, and the Arduino can relay that signal to whichever magnet is designated to release its weight.

Electrical Components
After assembling the Twister device, we turned our attention to the electrical components of the system. 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 the 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. Because of the complexity and customization of the original electric system, we chose to develop a new electric system, with a goal of making it as simple as possible without losing any features. 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, the interface communicates with the microcontroller, and commands are sent to the Motor Control and/or Sensory System. The microcontroller sends instructions to Motor Driver on how to move and how long to move. The microcontroller receives feedback from a photo resistor mounted on the inside of the turn table and gives positional data back to the microcontroller to be used for initialization and calibration. The Motor Driver receives specific voltages for specific movements desired for the DC motor. Each button related to the motor control on the interface sends a different character to the microcontroller. In the microcontroller code, each character is defined as a specific voltage output when it is called on. 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 useable 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.

Alternatives and Selection
Adding components to an aging system can prove to be difficult. Data types, operating systems, as well as the hardware changes over time. Originally, we were tasked in designing a new attachment centered around the existing equipment. During the early design stages, we found that we that the completion of the project using the original hardware and software provided would pose a significant challenge for the completion and long term success of the project. We feel that the only to meet our clients specifications of an easy to use, reliable, integratable system was to completely redesign the electrical and software systems. Our goal for the redesign is to implement a system with all of the specifications from the previous model as well as new specifications for the lateral movement attachment in the simplest possible way. The Motion Monitor motion capture system consist of an analog to digital converter that can be used to collect analog signals and analyze them through the movement software. Using this for data acquisition meets the client's specification of creating a real time data stream between the motion capture system and Twister mechanism, as well as simplify the hardware system. The Arduino Mega 2560 is a widely known microcontroller development board with large pre-installed and open source libraries. We chose this to communicate from the user interface because of its ease to use and implement into new system and the large resources and community that are available for it. A string potentiometer was used for tracking subjects movements when lateral forces are applied. We think using a string potentiometer connected directly to the user instead of a standard precision potentiometer seated in the pulley on the lateral perturbation attachment will prove to be a much more accurate way of tracking later 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.

Detailed Design
As stated earlier, we decided to redesign and modernize the existing electrical and software systems of Twister to provide a more reliable and permanent system. Redesigning the software allowed us to purchase a new computer since we were not restricted by an outdated .NET framework on the Windows 2000 platform. More modern methods of data acquisition were also enabled through the implementation of a new computer. Design specifications provided a need for Twister to be integrated with a motion capture system to compare movement data side by side in real time. To accomplish this, the subject movement data is outputted to the motion capture system. The analog to digital converter in the motion capture system accepts inputs through BNC connections. We are currently exploring how Motion Monitor handles the analog signals and will design the electrical system around this accordingly. The electromagnets are driven by an are driven by a digital signal supplied by the microcontroller. The microcontroller only operates at 5 volts and the electromagnets operate at 24 volts, so a solid state relay is used to trigger the power supply when a digital signal is received from the microcontroller over 2 volts. The motor is controlled by a motor controller, which can specify through variable voltage what operation the motor will be in.

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

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