Smart Walker Design ECE 480 TEAM 4 for The Resource Center for Persons with Disabilities (RCPD) Trevor Dirheimer Jeffrey Hancock Dominic Hill Yakov Kochubievsky Sean Moore Dr. Virginia Ayres - Facilitator Proposal Saturday, February 21st, 2015 Michigan State University 1
Table of Contents Executive Summary.....3 Sensor Concepts...3 Microcontroller Concepts 4 Feedback Concepts..6 Power Concepts...7 Design Concepts..7 Concepts and Feasibility Matrix of Design...9 Budget 13 Project Management Plan..13 Gantt Chart.14 References..15 2
Executive Summary: David is a bright, successful Michigan State University undergraduate student who has both visual and motor impairments. He recently fell down an unfamiliar flight of stairs on campus because he was not able to see the drop off as he approached. He turned this experience into an opportunity to solve this problem. Team Four of ECE 480 will build and design an intelligent sensor and feedback device to attach to David s walker. This device will alert and stop David from pushing and falling with his walker into dangerous drop-offs. The Smart Walker System will consist of four or more sensors with microcontroller integration and a rechargeable power supply. The Smart Walker Design project also involves a humanmachine interface dimension. Team Four will work with David to design experiments to determine the amount of time and distance needed to stop before falling, as well as implement the form of feedback he prefers for being warned of oncoming drop offs. David and others with mobility and/or visual disabilities will benefit from the Smart Walker Design feedback device because it will provide its users increasing confidence, safety and independence. Unexpected drop-offs and/or changes in the terrain pose the biggest hindrance to my independence and accessibility throughout campus and the community. My rehab doctor wondered if a simple "Roomba" knows not to go over an edge, why can't my walker? If there was a device that I could attach to my walker to warn me of changes in the terrain, I would have avoided the previously described accident. Anyone with mobility and/visual disabilities could benefit from such an innovation tremendously, increasing confidence, safety and independence -David Sensor Concepts: Goal: To detect sudden changes in elevation Candidate sensor types: Ultrasonic Sensing: The ultrasonic sensing concept involves sending an ultrasonic wave to a particular destination. The time elapsed between the incident wave and the reflected wave is multiplied by the speed of sound in order to determine the distance to the aforementioned destination. Ultrasonic sensors can have problems accurately determining the distance to a surface at a shallow incoming angle. The PING))) Ultrasonic Distance Sensor (Figure 1) is Team Four s top choice for the sensor option. 3
Figure 1 IR Sensing: The IR sensing concept involves triangulation. A pulse of light is emitted and reflected back. When the light returns, it comes back at an angle that is dependent on the distance of the reflecting object. IR sensors don t work accurately outdoors when there is direct or indirect sunlight. IR sensors also work poorly at long distances, although this may not be an issue in the present application. Team Four considered the Sharp Infrared Sensor (Figure 2) as the sensor option. Figure 2 Microcontroller Concepts: Deciding which microcontroller to use is a critical decision. Since the microcontroller will be constantly reading and writing data, it will need to be equipped with sufficient RAM to handle storage of multiple data points. Furthermore, it will also be necessary to have a microcontroller that has built in Analog-to-Digital converters (ADC) for its I/0 channels. The sensors will be sending data through an analog signal; of which, cannot be computed in the Central Processing Unit (CPU) until the signal is converted digitally. Based on the digital data, the microcontroller needs to algorithmically decide when to trigger the feedback system when a sudden drop off of elevation has occurred. Therefore, the 4
microcontroller needs to have desired 8KB-16KB of memory for storage. Due to slow speed of the user s movement with his/her walker, the sampling rate is relatively low. Therefore the microcontroller needed doesn't need to run off a high frequency. Low power consumption is another desired feature in the selection of the microcontroller as well. It will be necessary to have the microcontroller be powered by a low current supply and have the capability to execute in a standby mode. Figure 3 Texas Instrument s microcontroller, MSP430G2553 (Figure 3), meets all necessary features. This microcontroller has 16 digital channels that can be set to inputs and outputs. Eight of the 16 channels can also be use as ADC inputs; therefore we can use a maximum of eight sensors in the Smart Walker design. The MSP430G2552 also has sufficient flash memory of 16KB and 512B of RAM for data storage. The chosen microcontroller has 16 registers to reduce instruction execution time, which makes the CPU perform more efficiently and increases its processing speed. The MSP430G2553 doesn t require much power, as it typically draws 330mA during operation. It is also capable of running in five low power modes; therefore allowing the Smart Walker device greater energy efficiency. In addition, the wake up from these low power modes is less than 1ms, which allows the microcontroller to resume functions effectively and in a relatively small amount of time. Texas Instruments offers its own software, Code Composure Studios, which allows for running or stopping programs from execution at any given time. This allows the programmer to check variables and register values after each instruction is executed. Furthermore, Texas Instruments provides excellent documentation for the MSP430G2553 microcontroller. They offer a large, descriptive user manual guide and provide sample codes to get the user started. The versatility of Texas Instrument s software and hardware products are an excellent fit for the Smart Walker device project s needs. 5
Feedback Concepts: For the feedback system, Team 4 has chose to use an auditory system. During a meeting with David and team four s sponsors, David deeply expressed how an auditory system would be the best form of feedback to alert him of a sudden drop-off. Team Four s sponsor Stephen Blosser, IT specialist at RCPD, has donated an auditory feedback system that he created years ago. The feedback system will be triggered by the microcontroller and will alarm David with a repeated high frequency tone. The auditory system is powered on by minimum of 5V and starts beeping as soon as power is initiated. The microcontroller will output 5V to the feedback system, when needed, to alert the user of a drop-off. The two figures below (Figure 4,5) are the schematic and PCB layout of Stephen Blosser s auditory feedback design. Figure 4 6
Figure 5 Power Supply Concepts: Another key sub-goal is that the end product be ultralow power for long lasting battery life, so the warning system does not lose power during daily use. The micro processing unit will need to constantly take measurements from four sensors throughout most of the day. The MSP430G2553 is the chosen microcontroller unit; its active mode operates at 2.2V and 230μA at 1MHz, according to the data specifications. The operating frequency referenced in the data specifications is far greater than the frequency that will be used for our purposes; however, to accommodate any worst case scenarios this data is sufficient and estimates the power draw from the controller to be approximately 506μW of continuous draw. The microcontroller has built in power save states to conserve battery life. The benefits of using an accelerometer to put the device in standby, while not moving, will be investigated. The sensors currently being investigated will operate at 5Hz and require a 5V source to power them. These will be the bulk of the load the power bank will need to supply with a projected 600mW of continuos draw. The audio feedback circuit utilizes an IC with a boost converter, 7
which operates at.8v at 120μA when in use. This would only be about 96μW of draw, which would only last a few seconds and only be a factor when a drop off has been detected. The microcontroller will connect to a single rechargeable power bank. The chosen power bank is an ANKER Astro E5, which is rated at 16000mAh. This will be more than sufficient to power the system for 15 hours and offers approximately 600 lifetime charge cycles. The power bank will be charged via a micro USB port and will be easily removable from the unit housing to allow for overnight charging. Design Concepts: Our leading design concept is to utilize four ultrasonic sensors to detect a sudden drop in elevation along the user s path of travel. The sensors will be mounted to the front, backrest bar of the walker (Figure 6,7). The orientation of these will produce four distinct data points, which will allow for enough references for accurate triggering of the warning system. An audible warning system will be used to alert the user. These sensors will be mounted to the curvature of the mid-bar, with two facing directly forward and one angling in the peripheral direction on both the right and left side. Precise angling of the peripheral sensors is to be determined and will be optimized based on testing trials. All sensors will have the same vertical angle with respect to the surface being previewed. Mounting will be accomplished using screw clamps, which will be designed after further testing has been done. The microcontroller, power supply, sensors and associated connections will be safely contained in a modular bracket, that will act as a universal mount so users are not limited to any one particular walker. Figure 6 8
Figure 7 Selection Matrix of Design Concepts: The selection matrix is a system, which allows for evaluations and comparisons of prospective designs to be made. Design criteria will be assigned a level of importance (5 being the highest and 1 being the lowest). The solutions will be assigned a level of strength that corresponds to how well the specific solution meets the specific criteria (9 being the strongest and 1 being the weakest). In order to choose which solution best meets design criteria, each solution strength is multiplied by each respective criteria importance. The product of design criteria and solution strength will be summed in order to give each solution a value. In order to simplify the selection matrix, a system of abbreviations will be used to describe the functioning components of this design. Below is an abbreviation legend that translates component descriptions to a part code, with the format of quantity1: part code1, quantity2: part code2, etc. Abbreviations to Design Solutions Component Description Ultrasonic Sensor Detection System Infrared Sensor Detection System Shop manufactured Aluminum Harness and Housing 3D Printed plastic harness and housing Part Code US IR AL 3D 9 Volt battery 9V 16000 mah 5V Battery Pack 16kB 9
Table 1 For example: Team Four s design will utilize four ultrasonic sensors along with a TI microcontroller to trigger an audible alarm. This will be powered by an array of eight 9 volt batteries, all of which will be housed in a 3D printed plastic harness, the solution will simply read: (4: US, 8: 9VB, 1: 3D). The engineering criteria that received a rating of most importance was the ability to alert the user at least 4 feet ahead of a drop off because this ensures our user s safety. The battery life received a rating of 4, as running out of power would render this product useless. The ability to work outside, being transferrable to different walkers, durability, and avoidance to sensitivity to different surfaces were all functions that increased the usefulness of this product, but aren t critical to the core functionality. Aesthetics, while important for future marketing purposes, received a rating of 2 because safety is a direct result of the functionality for this product, not aesthetics. Engineering Criteria Importance Solution Strength Possible Solutions: (4: US, 1: 16kB, 1: AL) (4: US, 1: 16kB, 1: 3D) (4:IR, 1: 16kB, 1: AL) (4: IR, 1:16kB, 1: 3D) (4: US, 8: 9VB, 1: AL) Alerts User to a drop off at least 4 away 5 9 9 5 5 9 Can be transferred to different walkers 3 8 9 8 9 8 Can last for at least one day on full battery 4 9 9 9 9 1 Can be used outside 3 9 9 4 4 9 Functions with different ground surfaces 3 9 9 7 7 9 Can withstand moderate impact 4 9 6 9 6 9 Aesthetic Appeal 2 7 9 7 9 7 Selected Solution: (4: US, 1: 16kB, 1: AL) Totals 209 204 168 163 177 Table 2 The Smart Walker design will utilize four ultrasonic sensors along with a TI microcontroller to trigger an audible alarm. This will be power by 16000-mAh-battery pack. This entire arrangement will be housed in a shop manufactured aluminum harness. 10
Risk Analysis: The primary points of concern stem from the diverse environments that the system will need to perform. In addition to this, limitations of the sensors and their position must be considered. The Smart Walker is only limited by where the user will take it; therefore the goal is not to limit a user s mobility, but enhance it. The design will need to work inside and outside under any conditions that may arise from terrain and weather. For instance, there will be a variety of surface characteristics, such as reflectivity and softness that will need to be measured. The sensors rely on receiving an echo from an initial trigger and soft enough surfaces may dampen or completely absorb the trigger resulting in a false warning of a dropoff being sent to the user. The system will need to be weather resistant, as it will encounter sun, rain, and snow for any unknown periods of time throughout its lifespan. Along with weather concerns the system may encounter kinetic shock from being bumped against everyday obstacles or dropped while transferring the system from one walker to another. These possibilities can t adversely affect the system s operation. It s also expected that the device not run out of power during operation. The power source must reliably be able to support the average expected load of approximately 600 mw, for at least 15 hours. Constraints of the sensors and their position must be considered as well. Shown in Figure 8 below, a larger distance (D) is desired because it would provide an earlier hazard detection time (The user will be alerted to an elevation change 5 seconds ahead of time as opposed to 2 seconds). The sensing distance (D) is limited by the height (H), at which the sensor is mounted. Because height H is fixed to the crossbar of the walker, an increase in distance (D) would cause a decrease in angle (A). Both sensors have a transmitter to send out the incident wave and a receiver to detect the reflected wave. A lower angle (A) would greatly diminish the power of the reflected wave. This pitfall is common to both ultrasonic and infrared sensors. The PING))) ultrasonic sensor has a limit of a 45 incoming wave angle. The Sharp IR sensor also suffers from the same limitation. Therefore, a higher quality receiver is required to detect the reflected wave earlier. Please note that IR sensors are highly accurate, given lighting conditions are not too harsh. These sensors can see washed out responses if the user travels outdoors on a bright day as opposed to the high level of performance they see indoors. 11
Figure 8 FAST Diagram: Figure 9 12
Budget: Figure 10 Project Management: The Gantt chart below (Figure 11) includes the schedule of tasks and the personnel that will have a primary focus in completing them. This will provide Team Four with organization and understanding of when deadlines are. Success will be measured by Team Four s ability to stay on schedule and continue to meet goals. Through RCPD, Team Four has great resources in Susan Langendonk and Stephen Blosser. Susan has worked with David for the past couple of years and will provide valuable information specific to David s disabilities. In addition to this, Stephen Blosser is a mechanical engineer and will provide his machine shop to aid in creating the brackets and mounts for the sensors, circuitry and power supply. Along with each team member s administrative position, each team member will have a technical role to balance the workload. 13
Gantt Chart: Figure 11 14
References: PING))) Sensor: Ping Data Sheet Sharp IR Sensor: http://www.acroname.com/articles/sharp.html Sick Sensor: Data Sheet Sensor Reference Power Bank: http://www.amazon.com/gp/product/b00rvdjf82/ref=as_li_ss_tl?ie=utf8&m=a294p4x9 EWVXLJ&tag=ianker- 20&linkCode=as2&camp=217145&creative=399373&creativeASIN=B00RVDJF82 15