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.

Development and Project Goals
The Department of Neurology at Oregon Health and Science University developed the Twister device to study the regulation of tonic muscle activity during active postural maintenance. 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. []

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
Postural habits can greatly affect a person's life physically and mentally. Studies have shown that patients that had 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. 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 on a puddle. 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 tense as they get ready for the force. It creates 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 reassembly it. This helped us in the long term for learning how the mechanism worked and the way data was being collected from the torque sensors and 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. This 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 translate the torque signals into usable data for the data acquisition system. 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 a 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 3 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 data acquisition system was not shipped with the rest of the components.

Software
The Spike software accepts data from CED data requisitioning systems, which have a starting cost of $5000. With a project budget of $2000, we had to find another option. Spike analysis software runs on Windows 2000 OS. When researching new DACs we found no viable options that can run off of Windows 2000. 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. The motion capture system runs off of Motion Monitor software and collects data on how subjects move. Through research, we found that Motion Monitor can accept all analog signals and most digital signals and can translate those signals into usable data. The torque sensors produce an analog signal and we are currently selecting a rotary encoder that will meet the specifications required for data analysis by Motion Monitor. The Twister program was written in an early .NET framework and does not have the ability to be fully transferable to a newer Windows operating system. Motion Monitor runs off of Windows 7 and a later frame work, and for that reason, we are in the process of rewriting the DC motor control code. We will be adding extra functionality pertaining to the lateral movement mechanism addition to Twister.

Pulleys 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 12.25 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 not yet been determined but given preliminary calculations it seems reasonable that he weight required will not exceed fifteen pounds. Then, given a safety factor of two the electromagnets should have a holding capacity of roughly thirty pounds. Electromagnets in this range are usually 12 volt dc powered and require a positive and ground connection. When powered they are “on” and when there is no power they are “off.” Some specs of a common unit that might be suitable are listed below.

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, blue box, and black box. The silver box is the main electrical driver for the system. It contains power boards for powering the Torque sensors and DC motor, a microcontroller board, a signal conversion board, and input and output boards. The 2 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 splitter for the 37 pin cable. 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.