1 Child Passenger Safety Seat Team Members: Erik Bieging, Aman Ghotra & Karim Mahamud Client: Tom Brazelton, MD, MPH Dept. of Pediatrics – UW Hospital & Clinics Dept. of Pediatrics – UW Hospital & Clinics Advisor: Mitch Tyler Dept. of Biomedical Engineering Dept. of Biomedical Engineering

2 Recall: Background Existing Design: –Safest to transport children (<30 kg) sitting up in child seat attached to gurney in an ambulance [2] –For specific medical conditions, EMTs must unstrap child out of seat and remove the seat off the gurney to lay the child in supine position on the gurney [3] Limitations: –Seat does not recline –Seat is bulky

3 Problem Statement Develop a safe and compact child seat for transporting children (6-30 kg) in ambulances that allows Emergency Medical Technicians (EMTs) to recline the child in the seat from the sitting position to the lying position when strapped onto a stretcher.

4 Overview of the Prototype Last semester we designed a wooden prototype that had: –Recline Lock (A) –Sliding Strap (B) –Back Rest (C) –Leg Support (D) Overview of Design Concept

5 Overview of the Prototype Last semester we designed a wooden prototype that had: –Recline Lock (A) –Sliding Strap (B) –Back Rest (C) –Leg Support (D) Figure A: Design Concept Figure B: Design Concept

6 Overview of the Prototype Last semester we designed a wooden prototype that had: –Recline Lock (A) –Sliding Strap (B) –Back Rest (C) –Leg Support (D) Figure C: Design Concept Figure D: Design Concept

7 Accomplishments & Goals For The Semester PROBLEMS (Wooden Prototype) SOLUTIONS 1. Wooden Prototype is too HEAVY and BULKY 1. Build a NEW PROTOTYPE with light yet robust materials 2. Strap mechanism difficult to SLIDE and LOCK 2. Replace old design with Spring- Loaded Strap Mechanism 3. Did not Perform Prototype Testing last semester 3. Conduct Non-Destructive Testing

8 Force Analysis Max deceleration in a crash = 20g = 198 m/s 2 Max Child Mass = 30 kg Max tension in shoulder straps = (30 kg)(198 m/s 2 )/(2 straps) = 2970 N Maximum Forces: –F strap = 5.9 kN –F hinge = 65.2 kN –F pin = 71.2 kN –F track = 12.1 kN F hinge F track F strap F pin 24” 12” 2”

9 Materials Materials we intend to use for NEW PROTOTYPE –Safety Factor: 2 –HD Polyethylene Sheets Bulk Material (in place of wood) –General Purpose Aluminum Sheets For Reclining Mechanism –Estimated Mass: <3.5 kg

10 Accomplishments & Goals For The Semester PROBLEMS (Wooden Prototype) SOLUTIONS 1. Wooden Prototype is too HEAVY and BULKY 1. Build a NEW PROTOTYPE with light yet robust materials 2. Strap mechanism difficult to SLIDE and LOCK 2. Replace old design with Spring- Loaded Strap Mechanism 3. Did not Perform Prototype Testing last semester 3. Conduct Non-Destructive Testing

11 Spring-Loaded Strap Mechanism Spring loaded T-lock slides in slots in back of seat Locks into grooves created by blocks mounted to back of seat Stress on seat = (2970N)/(.25 in 2 ) = 2700 psi

12 Accomplishments & Goals For The Semester PROBLEMS (Wooden Prototype) SOLUTIONS 1. Wooden Prototype is too HEAVY and BULKY 1. Build a NEW PROTOTYPE with light yet robust materials 2. Strap mechanism difficult to SLIDE and LOCK 2. Replace old design with Spring- Loaded Strap Mechanism 3. Did not Perform Prototype Testing last semester 3. Conduct Non-Destructive Testing

13 Non-Destructive Testing On Locking Mechanism –Function: Prevents seat from collapsing –Collar around the pin has an unknown effect on the mechanism –Shear test on the pin to determine the type of collar

14 Non-Destructive Testing On Strap Mechanism: –From our calculations a force of 2970N is needed to break the strap –Conduct Tensile test To see the forces needed to break the strap Use tensile machine in the materials testing lab On the Back Track/Grooves –Conduct Tensile Test –Must withstand 2970N

15 Non-Destructive Testing On 5 Point Harness Buckle –Buckle prevents the child from being ejected in case of an accident –Tensile Test All 5 straps must withstand 2970N on each strap On Reclining Mechanism/Supports –Conduct Fatigue Test To determine the shelf life of the child safety seat Test by applying a static load and cyclic loading

16 Summary Design a NEW prototype –Light & Robust Materials Modify Strap Mechanism –Spring-Loaded Strap Mechanism Non-Destructive Testing –Determine durability/strength of the prototype

17 References [1] Safe Ride News. [2] Detroit News htm htm htm [3] Brazelton, T. University of Wisconsin Hospital and Clinics. Interview. [4] Physical Characteristics of Children.

18 Questions??