For more information, please contact

Transcription

1 Instrumented Pen Design Team Joe Ranieri, Chris Sullivan Evan Grey, Lauren Hess Design Advisor Prof. Andrew Gouldstone Sponsor Northeastern University Abstract This Capstone Design Project is to develop an instrumented pen that will measure the grip force the user applies while writing. The final design should be indistinguishable from a normal pen to avoid skewing data. This type of pen would be used in writing tests involving patients with Parkinson s disease (PD), to study how their grip force is affected by this disease. There are currently no products on the market that are able to quantify grip force while writing, without being obtrusive and cumbersome. Research revealed several sensors that could be integrated into the final design; however the focus was placed on the FlexiForce and TactArray systems. The FlexiForce (FF) sensor is a flexible force sensor that outputs a single force measurement, and the TactArray is a tactile pressure sensing cloth that outputs force over an entire area, and presents the data in a contour map. The FF sensor was chosen due to its low cost and ease of use and integration into a final design. Using an Arduino microcontroller and MatLAB, force over time will be recorded and graphed live. This pen will be used to gain access to another set of data points that researchers currently have no way of observing, and will help learn more about Parkinson s disease. For more information, please contact a.gouldstone@neu.edu

2 The Need for Project Northeastern is seeking a pen that measures grip force to aid in the research of Parkinson s disease This project was created to assist Northeastern University with research they are doing on Parkinson s disease. A successful outcome of this project will enable Northeastern University to conduct experiments on how a person s grip changes when experiencing a tremor. This is currently information that no one has access to due to lack of materials. The Design Project Objectives and Requirements To design and construct a pen that monitors the grip force a user applies throughout writing Design Objectives The goal of the Instrumented Pen project is to design and construct a pen that monitors the grip force a user applies throughout writing, particularly for patients affected with Parkinson s disease (PD). Parkinson s disease is a digressive, degenerative neurological disease. It is a movement disorder, meaning that as the disease progresses; body movements such as walking and talking are affected. The completed pen will be used as a characterization tool in a Northeastern University research project to study writing in PD patients. Tremors are the most common symptom of PD and consist of uncontrollable shaking primarily in the hands. This pen would help build connections between grip characteristics, writing performance, PD severity, and therapy. To be useful to the research group, the pen must have two primary characteristics, which the group considered in their design goals: 1) The pen must provide a pressure map of grip, throughout a writing exercise. 2) The pen must be indistinguishable from a typical pen, to avoid and skewing of data. Design Requirements The final design of the pen will output the amount of force the user applies on each of the pens sensors. This data will be outputted to a graph in real time and the data can be easily exported to other computer programs for further analysis.

3 Design Concepts Considered We developed two candidate The team had several ideas for the initial design of the writing design concepts of which one instrument. After much brainstorming it was decided that there were fully meets the requirements two ways to present the final design: wireless, or attached to a table with a cord. One of the initial goals of this project was to create a pen that does not deviate from the design and feel of current pens, leading the team to immediately decide wireless was the way to go. Once taking a step back and reexamining the problem, it was brought up that many pens are also attached to surfaces (like at the bank, attached to a clipboard) for several reasons. After realizing that attached pens are not that uncommon, this idea was also evaluated closer. The first idea was to make the pen totally wireless. This would require a power source, as well as data acquisition system on board. The team decided that it would make the top of the pen wider to accommodate a power source as well as a data acquisition system. The entire length of the pen would be coated by a tactile sensor array that would be able to record pressure at any point on the pen. The pen could then be plugged into the computer to read and analyze results. This pen would be totally portable and could easily be used anywhere. However, designing and manufacturing a pen to hold a power supply and data acquisition system could prove to be difficult. Nevertheless, in consideration of this, the team is exploring how the pen COG would remain consistent with typical models in such a case. The second design concept would be a pen that would be similar to a pen you would see in a bank. It would be similar to the wireless pen in that it would have a pressure sensor wrapped around the exterior of the pen. However, this pen would have a spiral cord similar to one found at a bank, that would transmit pressure data to a hidden data acquisition system. Recommended Design Concept After careful though it was decided that the Bank Pen was the best design concept to follow through on. Design Description The final design chosen by the team was the concept of the bank pen with the FlexiForce sensors. In this design, there are six strategically placed sensors around the bottom 1/3 of the pen. These sensors are underneath a rubber grip to conceal them. The wires are then fed through slits to the inside of the pen, and are fed out through the top. The shape of the pen was chosen to be a triangle; this allowed

4 for the sensors to lie flat, rather than molded to the curvature of a round pen. The sensors are wired to an Arduino microcontroller, which transmits the data via USB to the workstation and plots the force vs. time in MatLAB. Experimental Investigations Throughout the design of this pen, many experiments and tests were done to prove that the concept chosen worked. At first, the sensors were wired up simply to a DAQ ; this proved that the sensors would capture very small changes in force (similar to those experienced while writing). Once it was proven that these sensors were a good fit for the design, they needed to be calibrated. This was done using a linear actuator and a digital scale. A constant force (in grams) was applied to the sensor, and then the corresponding voltage output was recorded. These data points were used to make a calibration curve to convert voltage to force (grams). The sensors were incorporated into the final pen design (two placed on each surface of the pen) and then covered with a rubber grip. The six sensors were wired up to the Arduino, and MatLAB outputted 6 graphs, one for each sensors. Key Advantages of Recommended Concept One of the main goals of this Capstone Design Project was to create a pen that would measure grip force while still being indistinguishable from a regular pen. By using a pen design already on the market and hiding the sensors under a rubber grip, along with feeding the wires through into the pen, this design accomplishes that goal. The pen will work no matter which way the user holds it (due to its triangular shape) and because of the visual cues placed on the pen, the researcher always knows which sensors are falling under which finger. It is not awkward or bulky to hold (as the wireless design would have been) and feels comforatable in the users hand. Each sensor on the pen corresponds to its own graph in MatLAB, which makes troubleshooting this pen a lot easier. If one of the sensors is not outputting properly, the researcher can automatically narrow it down to the one sensor that is malfunctioning, rather than testing each of the six. Another key advantage to this design is that the person conducting the test does not have to know much about MatLAB. The program was written so that the outputted data can be viewed in real time on a graph, but it can also be easily imported into Microsoft

5 Financial Issues The price for this project was around $200. Excel. This is important because it allows the data to be looked at in real time, or analyzed at a later date. The main costs for this project were the purchasing of the Flexiforce sensors which were $20 each. Other purchases for this project were a proto-board to experiment on different circuit layouts for multiple sensors, two Arduino circuit boards, and a bank pen to connect our sensors and wires to for the final design. Recommended Improvements The main improvement to this project would be to make the pen work wirelessly. One way this project could be improved upon would be to design it so that it would work wirelessly. This would be an improvement because the pen would furthermore be disguised as a normal pen and would also be more user-friendly if all the data acquisition hardware was internal and would automatically record data upon writing.