Feedback Pen and Smart Stencil: A Handwriting Correction Tool

1. Feedback Pen and Smart Stencil: A Handwriting Correction Tool Group 41 Corey Paney Sarah Schonert Neville Vazifdar

2. Introduction Problem 1 – Carpal Tunnel Syndrome (CTS) • Can be caused by repetitive use of hands, with median nerve damage especially involving thumb, index, and middle finger. • Can be prevented by using less force with performing tasks with the hand (such as writing) and using a large, oversized pen. http://www.mayoclinic.com/health/carpal-tunnel-syndrome/DS00326

3. Introduction Problem 2 – Poor Handwriting: • Correct posture, correct finger placement and a more relaxed grip is recommended by the creators of D’Nealian Handwriting. • Correct finger placement often eases the grip. • Posture can be helped by easing the force exerted onto the paper, (the more force one feels is needed, the more likely one is to slouch over the paper).

4. Introduction Possible candidates for the use of the pen: • Children learning to write. • Adults recovering from an accident or surgery needing to relearn how to use their hands (this would include carpal tunnel sufferers). • Children and adults with physical disabilities and those at risk for carpal tunnel.

5. Objective The pen should: • Have feedback on finger placement and force exerted downward on the pen. • Require little force on any buttons that relay finger placement.

6. Objective The stencil should: • Provide feedback on whether the user hits the sides of the stencil • Come in two parts: a base and a removable stencil (possibly several that may be interchanged). • Involve the strokes (such as swoops and lines) required to make proper letters. • Attach TO the pen so that the pen may be used separately.

7. Overview

8. Stencil

9. Design: Stencil Original Plan The stencil’s circuit is closed only when the pen touches the edges of the stencil, causing an LED to light up.

10. Design: Stencil Original Stencil Design

11. Design: Stencil The pen must connect to the stencil

12. Building the Stencil Circuit Parts List: • 1 LED – green • 2 AAA batteries • 1 2-AAA battery holder • 1 10 Ohm resistor • 1 LM334 – Current source • 1 2N2907 – BJT

13. Building the Stencil Structural • Plastic (cut professionally) • 4 Plastic corner braces • Wooden dowel rods • 1 input jack • 1 output plug • Copper sheeting for embossing • Screws and double-sided sticky tape • The circuit fits on the bottom-most plastic panel.

14. Building the Stencil • The stencil fits snuggly into the base with enough room to fit a piece of paper in with it. • The pen tip is conductive and is connected to a wire attached to a jack at the top of the pen.

15. Stencil Safety Concerns The following chart shows that overheating is of no concern for the stencil circuit. The temperature of the copper was measured with time, keeping in mind that contact time will be much less. Also, the stencil functions off of 3V and never outputs more than 13mA, so electric shock is not an issue.

16. Finished Stencil Stencil Base (without stencil removable stencil)

17. Finished Stencil Stencil and Base

18. Stencil: Cost Analysis Cost Estimate • Circuitry - $5 • Batteries - $1 • Misc Parts + Labor - $50 TOTAL - $56

19. Finger-Placement Feedback

20. Design: Finger-Placement Feedback • The goal is to have the thumb, forefinger, and middle finger on the optimal locations of the pen.

21. Design: Finger-Placement Feedback • For the grips themselves, we used non-tactile membrane switches. • These switches were effective because they didn’t require much force to close, which is desirable because we didn’t want to reinforce bad habits of gripping the pen too tightly.

22. Design: Finger-Placement Feedback • The original logic design included correct and incorrect grip switches, and corresponding LEDs.

23. Design: Finger-Placement Feedback • The final design used only correct grip switches and required only one chip, saving valuable space in the pen.

24. Design: Finger-Placement Feedback • The output of the logic went to the Vcc of the Constant Current Source, which supplied the power for the LED.

25. Building the Pen: Finger-Placement Feedback Circuit Parts List for Grips: • 1 LED – red • 1 SN74LS20 chip – Four input NAND • 3 Five K Ohm resistors • 2 Fifteen Ohm resistors • 3 Membrane switches • 1 LM334 – Current source • 1 2N2907 - BJT

26. Functional Tests: Finger-Placement Feedback • Most straightforward test was in connecting the membrane switches to the logic and then seeing if the LED would come on when all switches were not tripped.

27. Building the Pen: Finger-Placement Feedback Successes • Membrane switches were an effective way to create correct grip monitoring. • Logic worked as desired.

28. Building the Pen: Finger-Placement Feedback Challenges • Logic gates required more power than expected, so we had to use a much bigger battery. • Membrane switches were sometimes too touchy.

29. Constant Current Source Constant Current Sources were used to power the LEDs in order to minimize power loss, as well as for the purpose of allowing each LED to receive its desired current despite battery drainage. LED Current = 0.065/R1

30. Constant Current Source • Initially, each LED was to be powered by a constant current source. However, only the Stencil LED and Finger-Placement LED used constant current sources because there was not enough space in the pen to implement another one for the Force Feedback Circuit. • The idea of using a relay for the two pen LEDs was proposed, but the relays found were far too bulky and defeated the purpose of using only one constant current source. • For future implementation, very small constant current source chips are available to drive multiple LEDs. The reason for not using such a chip in this design was to be able to implement such a circuit independently.

31. LED Waveforms Red LED Voltage Ripple

32. LED Waveforms Green LED Voltage Ripple

33. Force Feedback

34. Design: Force Feedback • In order to give accurate feedback on the downward force placed on the pen tip, we used a spring that would contract just slightly when an excessive mass is applied (approximately 50 grams since 40 grams is required for writing with the average ball point pen). • The length that the spring contracts due to the 50 grams applied (3.5 mm) was calculated using standard hook masses and finding the spring constant. F = -kx , k = 140.1 N/m Occupational Hazard Reference http://www.mpatkin.org/ergonomics/occ_strains_children.htm

35. Design: Force Feedback • When the downward force applied exceeds that which is required for the spring to contract 3.5 mm (1.5 mm more than the 2 mm by which the spring is always contracted in the pen), the switch is triggered and the corresponding LED (green) lights up. • The circuit is very basic; the LED with load resistor is connected to ground and to the force trigger.

36. Design: Force Feedback Chart of Length Contracted vs. Mass for Spring (including significant point markers)

37. Design: Force Feedback • This spring design was implemented rather than using just a force or pressure sensor because the spring minimizes the friction that would otherwise be created by the pen tube rubbing directly against the outer plastic tube or other guide. • An implementation using both the spring and a force or pressure sensor would work well in reducing friction but would then require both the contraction of the spring as well as the sensor to monitor the force, whereas in the current system, the spring is able to do so independently.

38. Design: Force Feedback Original Diagram of Spring System

39. Building the Pen: Force Feedback Actual Implementation of Spring System

40. Building the Pen: Force Feedback Circuit Parts List for Force Feedback: • 1 LED – green • 1 Two K Ohm Resistor • 1 8mm x 25mm Copper strip • 1 6V Lithium Battery (160 mAh) • 1 SPDT Slide Switch

41. Functional Tests: Force Feedback • After completed assembly of pen, two basic functional tests were required in testing the Force Feedback module. • Ensuring that the LED remains off until a force is exerted on the pen tip. (Functioned as desired.) • Testing for the desired minimal force of 50 grams required to trigger the LED using the same hooked masses used in the original testing of the spring. (An excess of approximately 10-20 grams was required to trigger the switch and LED.)

42. Building the Pen: Force Feedback Challenges • Accurate construction and placement of all parts involved took multiple trials and much patience. • Precision of placement in reducing friction required a multitude of corrections to the original design. • Assuring that spring system remained physically isolated from all other parts of the pen was a significant factor in deciding the length of the pen as well as the placement of various circuitry and mechanical parts within the pen. • Once the module was integrated into the pen, much care had to be taken to ensure that the module remained untouched during the process of assembling the remaining pen parts as well as the complete assembly of actually closing the pen.

43. Building the Pen: Force Feedback Successes • Due to a prior assembly for the mock demo, certain initially unapparent issues had already been trouble-shooted. • The Force Feedback module worked as desired aside from a slight excess of mass required to trigger the LED (approximately 60-70 grams required as opposed to the desired mass of 50 grams). • The pen tip (ink refill) is easily replaceable with current implementation.

44. Building the Pen: Final Assembly Pen Casing The plastic casing from a standard marker was used for the outer casing of the pen.

45. Building the Pen: Final Assembly Intermediate Construction • Assembling circuitry and intermediate parts while still allowing space within the pen for all components posed quite a challenge. • Intermediate testing of the functionality of all components was necessary after the implementation of each subsequent element of the pen.

46. Building the Pen: Final Assembly Final Construction • The Feedback Pen’s final implementation and construction proved to provide the desired functionality and, aside from the minor discrepancies discussed earlier, performed to the standards set in the initial pen objectives.

47. Feedback Pen Power Analysis • Total Voltage Output of Circuitry = 6V • 6V Battery Used • Maximum Current Output of Circuitry = 31mA • 23mA for Finger-Placement Feedback Circuit • 8mA for Force Feedback Circuit • Battery Rated at 160 mAh • Battery Life at Max Current Output = 5.2 Hours

48. Feedback Pen Safety Concerns • Temperature of pen never exceeds that of an average pen during regular use; circuitry in no way significantly affects temperature of pen. • The 6V battery used and maximum current output of 31mA pose no harm in terms of electric shock. • If designed and implemented correctly, pen should help decrease user’s chances of excessive strain during handwriting as well as decrease the chances of getting Carpal Tunnel Syndrome.

49. Feedback Pen: Cost Analysis Cost Estimate • Circuitry - $9 • Membrane Switches – Donation • Battery - $9 • Pen Refill + Misc Parts - $2 TOTAL - $20

50. Cost Analysis Salary = (5 hours/week) x (12 weeks) x (2.5 overhead) x ($45 per hour) = $6,750 per person $6750 x 3 people = $20,250 total for labor Labor + Cost of Pen + Cost of Stencil = $20,326 Preferred Cost for Mass-Produced Pen & Stencil - $75