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  • FINAL REPORT

    Adjustable Back Angle Controller (ABAC)

    By Alaena DeStefano

    Steven Frisk Raymond Pennoyer

    Team No. 8

    Funded by: Rehabilitation Engineering Research Center

    Client Contact Information Dr. John Enderle

    University of Connecticut: Biomedical Engineering Department Program Director & Professor of Biomedical Engineering Bronwell Building,

    Room 217C 260 Glendale Road, Storrs, Connecticut 06269-2247 Voice: (860) 486-2500

    Email: jenderle@bme.uconn.eduWebsite: www.eng2.uconn.edu/~jenderle

    BME Program Homepage: www.bme.uconn.eduEMB Magazine Homepage: www.EMB-Magazine.bme.uconn.edu

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    mailto:jenderle@bme.uconn.eduhttp://www.eng2.uconn.edu/%7Ejenderlehttp://www.bme.uconn.edu/http://www.emb-magazine.bme.uconn.edu/

  • Table of Contents Page Abstract 1 1. Introduction 1-6

    1.1. Background 3 1.2. Purpose of the project 3-4 1.3. Previous Work Done By Others 4-6

    1.3.1. Products 4-5 1.3.2. Patent Search Results 5-6

    1.4. Map for the rest of the report 6 2. Project Design 7-61

    2.1. Design Alternative 7-45 2.1.1. Design 1 7-18

    2.1.1.1. Objective 7 2.1.1.2. Control Lever 7-8 2.1.1.3. Lever 8-9 2.1.1.4. Hydraulic Control Valves 9-10 2.1.1.5. Resistance Springs 10-11 2.1.1.6. Hydraulic Pump/Motor 12-13 2.1.1.7. Motor 13 2.1.1.8. Hydraulic Tubing and Fixtures 14 2.1.1.9. Pressure Valve 14-15 2.1.1.10. Pressure Gauge and Adapter 15 2.1.1.11. Hydraulic Lift 15-17 2.1.1.12. Polycarbonate Box 17-18

    2.1.2. Design 2 18-32 2.1.2.1. Objective 18 2.1.2.2. Control Lever 18-19 2.1.2.3. Lever 19 2.1.2.4. Resistance Spring 19-20 2.1.2.5. Electric Circuit 20-25

    2.1.2.5.1. Overview 20-21 2.1.2.5.2. Potentiometer 21-23 2.1.2.5.3. Inverting Amplifiers 23-24 2.1.2.5.4. Difference Amplifier 24-25 2.1.2.5.5. Filter 25

    2.1.2.6. Electric Motor 25-26 2.1.2.7. Actuator 26-31 2.1.2.8. Support Frame 32

    2.1.3. Design 3 33-45 2.1.3.1. Objective 33 2.1.3.2. Control Lever 33

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  • 2.1.3.3. Lever 34 2.1.3.4. Resistance Spring 34-35 2.1.3.5. Electric Circuit 35-38

    2.1.3.5.1. Overview 35-36 2.1.3.5.2. Potentiometer 37-38

    2.1.3.6. Electric Motor 38-39 2.1.3.7. Actuator 39-43 2.1.3.8. Support Frame 43-45

    2.2. Optimal Design 46-61 2.2.1. Objective 46 2.2.2. Subunits 46-59

    2.2.2.1. Control Lever 46-47 2.2.2.2. Lever 47-48 2.2.2.3. Resistance Springs 48-49 2.2.2.4. Electric Circuit 49-52

    2.2.2.4.1. Overviews 49 2.2.2.4.2. Circuit Components 49-52

    2.2.2.5. Electric Motor 52-53 2.2.2.6. Actuator 53-59 2.2.2.7. Support Frame 59

    2.2.3. Testing the Design 59-61 3. Realistic Constraints 61-63 4. Safety Issues 63-66 5. Impact of Engineering Solutions 66-68 6. Life-long Learning 68-70 7. Budget and Timeline 70-74

    7.1. Budget 70 7.2. Timeline 70-74

    8. Team Member Contributions to the Project 74 8.1. Team Member 1: Alaena DeStefano 74 8.2. Team Member 2: Raymond Pennoyer 74 8.3. Team Member 3: Steven Frisk 74

    9. Conclusion 75 10. References 76-77 11. Acknowledgements 78 12. Appendix 78-90

    12.1. Updated Specification 78 12.2. Purchase Requisitions and FAX quotes 78-90

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  • Figures and Tables Page Flow Chart 1: Optimal Flow Chart 2 Figure 1: Invacare Adjustable Hospital Bed 4 Figure 2: Full-Electric Hand Pendant 5 Figure 3: Air-Powered Adjustable Bed 5 Figure 4: Flex-A-Bed Base 5 Figure 5: Basic Design of Handle 9 Figure 6: Control Valves 10 Figure 7: Calculation of Input Force on Springs 11 Figure 8: Free Body Diagram of Lever 11 Figure 9: PROCON Series 4 Pump 13 Figure 10: 48YZ Frame Motor 13 Figure 11: Hose Connectors and Hydraulic Hosing 14 Figure 12: Pressure Valve Regulator 15 Figure 13: Pressure Gage and Adapter 15 Figure 14: Prince Double Acting Hydraulic Cylinder 16 Figure 15: View of Intermediate Trunnion Mounting Style 17 Figure 16: Clear Polycarbonate Sheets 17 Figure 17: Overall Design Schematic 18 Figure 18: Circuit Schematic 21 Figure 19: Typical Rotary Potentiometer 22 Figure 20: Internal Workings of Rotary Potentiometer 22 Figure 21: Op Amp 23 Figure 22: Inverting Amplifier Circuit 24 Figure 23: Differential Amplifier Circuit 25 Figure 24: Circuit for a Series Wound DC Motor 26 Figure 25: Worm Gear/ Lead Screw Drive System 27 Figure 26: Overall Schematic at 0 Degree Angle Design 2 28 Figure 27: Overall Back and Side View of Schematic at 70 Degrees Design 2 29 Figure 28: Free Body Diagram of Lifting System 30 Figure 29: Linear Actuator Mounting Bracket 31 Figure 30: Properties of Aluminum-Beryllium 80-20 32 Figure 31: Electric Circuit Overview 35 Figure 32: LM324 Quad Op Amp 37 Figure 33: MOSFET 38 Figure 34: Free Body Diagram of Pin at 70 Degrees 40 Figure 35: Free Body Diagram of Pin at 0 Degrees 40 Figure 36: Graph of Force on Rod vs. Back Angle 42 Figure 37: Overall Schematic at 0 Degree Angle Design 3 44 Figure 38: Overall Back and Side View of Schematic at 70 Degrees Design 3 45 Figure 39: Basic Inside Design of Handle 47

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  • Figure 40: Push-to-Make Switch and Bracket Representation 48 Figure 41: PSPICE Simulation of Comparator Output 51 Figure 42: MOSFET Switching Response to PWM 52 Figure 43: Diagram of Scissor Jack Lifting Bed Back 54 Figure 44: Free Body Diagram of Lifting System 54 Figure 45: Free Body of Scissor Jack (Assuming Jack is a Rigid Body) 55 Figure 46: Diagram of Forces on Scissor Jack 56 Figure 47: Acceptable travel Rate vs. Length of Screw 58 Figure 48: Ball Screw 58 Figure 49: Overall Schematic at 0 Degree Angle Optimal Design 61 Figure 50: Overall Back and Side View of Schematic at 70 Degrees Opt. Design 62 Table 1: Bore Size Effecting Weight Lifted by Cylinder 16 Table 2: Calculations of Force on Rod as Angle of Bed Changes 42 Table 3: Estimated Budget 70 Table 4: Timeline 70-74

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  • Abstract The Rehabilitation Engineering Research Center (RERC) on Accessible Medical Instrumentation (AMI) is sponsoring the 2006-2007 National Student Design Competition. The proposed design is for an Accessible Power-Assist Hospital Bed Back Angle Controller which accommodates a wide range of patients and users of all disabilities. The basic design consists of a lever handle that controls a circuit which powers a mechanical actuator attached to the back of a bed to adjust the angle. The actuator will keep a low profile in the back so that it can fit neatly under the back of the bed and still have the bed lie completely flat. This is possible with a scissor jack that can collapse easily and it is operated by a motor which turns a screw rod to provide a smooth lift. The key features to this device are its safety lock to prevent accidental movement, the control lever which increases the speed with the amount of force applied to it, and the intuitive approach to operating the handle such that lifting the handle will give the sensation of lifting the back angle upwards and visa versa. The handle design itself will be large and easy to grip or find for those with poor vision or arthritis in the hand. There is no confusing interface or technology associated with this device. The motivation of the project is to build a totally accessible device to anyone using it. 13. Introduction

    Nursing is among one of the highest risk occupations for the development of back pain and injuries. Currently 17% of nurses experience chronic back pain due to working in a hospital setting. 36% of these back injuries in nurses can be contributed to patient handling. In addition to the back pain, women are also twice as likely to contract musculoskeletal disorders from the following work tasks: repeatedly lifting greater than 7 lbs, lifting patients more than 10 times per hour, making beds normally or often, and pushing beds or trolleys more than 10 minutes per day [1]. These daily tasks cannot be avoided; however, by the implementation of an automatic adjustable bed, nurses will incur less stress on their back during the adjustment of the patient.

    Patients that suffer from back pain, obesity, and other debilitating diseases,

    require an inclined bed back to relieve pain or provide easy access to the bed. Current technology includes an adjustable bed back with a remote control that is accessible for both the patient and the caretaker. However, this does not accommodate users of all disabilities. For example, a patient with limited sight may find it difficult to find the remote or press the correct buttons to operate the bed. Some of the current beds that may operate at higher speeds are rough or jerky when stopped in position. This erratic movement also occurs in beds that have more than one speed.

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  • Flow Chart 1: Optimal Flow Chart

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  • The Adjustable Back Angle Controller (ABAC) will improve upon the current

    methods of adjusting a bed. This device will be controlled with a force sensitive handle located on the most accessible side of the bed. The basic concept of adjusting the back angle will take the input force on the handle and adjust the speed proportional to the force applied to the handle, i.e., more force on the handle