Multidisciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623 P16041: Smart Walker IV Alex Synesael Alexei Rigaud Electrical Engineering Electrical Engineering Danielle Stone Stephen Hayes Electrical Engineering Electrical Engineering ABSTRACT Diagnostic medical technology in its current form is typically expensive and intrusive to a patient’s lifestyle. The purpose of the Smart Walker IV project was to finalize a robotic assistive walker prototype capable of collecting long-term diagnostic information about a patient’s health and activities. This gives care providers a more complete image of their health than can be achieved during a relatively short visit. In addition to the diagnostic features, Smart Walker is capable of autonomous motion such that it can provide emergency support in the event of a fall, or contact the appropriate third party support. Smart Walker IV is a culmination of three previous prototype versions spanning 2013 through 2015, and is intended to serve as the final revision before the platform is ready to be utilized as a graduate research platform for robotic assistive medical diagnostics. The goal of Smart Walker IV is to complete the build and integration phases from where the previous Smart Walker III team ended. The project progressed through analysis and completion of the existing systems, the design and testing of new diagnostic subsystems, and finally complete system integration and qualification. BACKGROUND Smart Walker began as a diagnostic tool for elderly people, and has since evolved into a research platform. The Smart Walker can take diagnostic measurements, as well as measure vital signs and detect when a patient has fallen. There is also potential for the Smart Walker to have autonomous motion capabilities in order to assist patients if they have fallen. The Smart Walker measures heart rate through contacts in the handles, which is a simple vital sign that can be used for diagnostic purposes. The Smart Walker can also measure body composition, which when used as a comparative measurement across relatively short periods of time, can detect a particular condition that is common in the elderly. This condition causes the body takes on copious amounts of water, which can eventually lead to death if not treated as quickly as possible. The Smart Walker also measures the relative force being applied to each of the two handlebars. This feature can be used in a diagnostic setting in order to determine whether or not a patient favors one side over the other, which could be indicative of pain or various other ailments. The Smart Walker is able to detect the possibility of a user to develop bedsores as well. As people age, the impulse to shift one's’ position lessens. When a user sits down onto the seat of the Smart Walker, a measurement is done in order to determine the overall XY position of the user. Over time, the Smart Walker will continue to perform this measurement and will note how often the user shifts their position. If the user is not moving frequently enough, they may need to be more closely monitored in order Copyright © 2016 Rochester Institute of Technology Proceedings of the Multidisciplinary Senior Design Conference Page 2 to ensure they do not develop bedsores. The Smart Walker also has the ability to track motion relative to a fixed point in order to provide for potential autonomous motion, as well as analysis of the gait of the user. The project received from Smart Walker III had the basic structure of the walker largely completed, and a walker that had sensors and controls partially integrated was received. The walker had an Xtion camera, strain gauges on each handle, four strain gauges on the seat, sensors electrodes on the handles, a body composition measurement sensor (BCM), and a Chronos watch. The electrical control system consisted of a PandaBoard microcomputer, an Arduino Mega, and custom PCB breakout boards. There were problems with some of the sensors as the PandaBoard had difficulties with SPI connections. The strain gauges on the seat and handles read values and sent them to the PandaBoard, but needed to be calibrated. The Chronos watch was programmed to detect steep changes in acceleration and sent a flag to the PandaBoard to indicate the subject had fallen. Mechanically, the walker had a semi-functional motor drive system that consisted of a 3D printed clutch and 12V DC motor on each of the front legs of the walker. The clutch could not disengage after being engaged, and there was an unbalanced moment being placed on the axis that caused grinding of the gears. DESIGN The Smart Walker drivetrain consists of a three major components, the drive motor and gearbox, an electromagnetic friction clutch, and a high-resolution driveshaft-mounted rotary encoder. This subsystem was given a major design overhaul from that of previous Smart Walker revisions in order to fix fundamental functional issues as well as to improve the patient’s experience overall. The current design can be seen in Figure 1 below with all major components labeled. Figure 1 - Overview image of drivetrain The prime mover of Smart Walker IV’s drivetrain is a Pololu-brand 12v DC motor with an integrated 50:1 metal gearbox. This motor was recycled from the previous drivetrain design and includes a 64 counts-per-revolution (CPR) hall-effect rotary encoder which is no longer used in favor of a higher-resolution shaft-mounted alternative. Powering the DC motor is a Pololu-brand 5A Arduino-compatible motor shield capable of driving both motors simultaneously. The rotational motion generated by the motor is coupled to the clutch armature/hub assembly via a set of hardened-steel bevel gears that provide another 2.7:1 gear ratio. This hub/gear assembly is let to freely rotate on the drive shaft by way of an oil-impregnated brass bushing until the clutch is activated with the requisite 24v DC. With the clutch engaged there is a friction-based interlock made between the drive shaft and motor that provides rotational Copyright © 2016 Rochester Institute of Technology Proceedings of the Multidisciplinary Senior Design Conference Page 3 action to the wheels. This design allows the patient to feel no perceivable resistance from the motor or drive gears when the clutch is disengaged and the drivetrain behaving in a passive state. A key feature of this revamped design is the ability to track the wheel rotation during both the active and passive clutch states, thereby allowing the encoder values to be utilized as high-reliability odometry data for both the analysis of a patient’s walking behavior and gait, and for future use in a SLAM algorithm. The encoder resolution of 720 CPR allows the actual wheel location change to be measured and tracked with under 1 millimeter of precision. These per-wheel measured distance change values are used in (Equation #) to extrapolate the walker’s location and angle with respect to a starting origin point. The Chronos watch is used in order to detect when a user falls or requires other immediate assistance. The watch contains an accelerometer, which is used in order to detect when the watch goes into freefall. When this occurs, a fall flag is sent over to the ODROID and the X, Y, and Z data from the accelerometer gets placed into a table in MySQL in units of gravitational force, or Gs, along with a timestamp. If the user requires immediate assistance, they can press any of the buttons on the Chronos watch. This button press will also send the accelerometer data, as well as a timestamp, to the MySQL table. The gripper rework was performed in order to enable the use of a metal contact for the heart rate and body composition measurements. The new contacts were designed in order to give maximum contact to the user’s hand, as well as appear clean and integrated with the system. The Smart Walker IV team made some changes in the hardware, therefore the enclosure used by the Smart Walker III team did not provide the cleanest housing solution for the components. A new enclosure was chosen that has a flip open lid that snaps shut, which allows for easier access to the internal components if need be. This new design also utilizes a mounting board inside of the enclosure, which enables all boards and components to be mounted cleanly without the need to drill holes through the overall enclosure. The handle strain gauges on the Smart Walker are used to detect balance or lean of the patient while they are using the walker; it can also be used as the primary detection method for when the walker is in use. The handle strain gauges are in a Wheatstone bridge configuration that provides linearity, improved output sensitivity and reduced thermal sensitivity. The Smart Walker III team had the strain gauges attached and measurable on the old PandaBoard control unit through an ADC. Figure 2 - Strain Gauge Configuration for Wheatstone Bridge The Smart Walker IV team changed the control unit to an ODROID XU4, added to the data processing as well as created the data storage system in the form of a MySQL table that stores both handles raw data input as well as the processed percentages used to find patient balance with timestamps. The other goal of Smart Walker IV was to characterize the strain gauges, (see test results) and clean up the appearance of them. To have a clean look, the team will add a foam jacket with a heat shrink cover over the strain gauges. The four seated load cells underneath the seat can be used to find the center of gravity of the patient while sitting using statics and geometry.