University of Wisconsin Madison Biomedical Engineering Design Courses

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Hospital Bed-Back Angle Controller RERC National Design Competition Team Members Advisor Katy Reed Brenton Nelson Ibrahim Khansa Shikha Dr. Willis Tompkins Client Dr. John Enderle - University of Connecticut

Background: Current Hospital Beds • Disadvantages: o. Lack of usability §No velocity control o. Ergonomically poor §Buttons are hard to push §Buttons are not easily accessible

RERC National Design Competition • RERC: Rehabilitation Engineering Research Center • Conducts projects in Accessible Medical Instrumentation (AMI) • Competition organized by Marquette University and the University of Connecticut • 10 projects funded every year • Client: Dr. John D. Enderle, Professor of Biomedical Engineering at the University of Connecticut.

Problem Statement An intuitive hospital bed control system, which gives the user better control over the velocity of bed-back elevation, is desired. The user would be able to operate the bed-back through an ergonomic controller, and the velocity would vary with the amount of force applied.

Requirements • Ability to control velocity • Accessible for patients with specific disabilities • Intuitive and ergonomically designed controller • Support a maximum load of 180 lbs on the bed-back • Bed-back brake system during power loss • Maximum operator force should not exceed 20 lbs on the controller • Budget less than $2, 000

First Semester Overview 1. Feedback loop design o Fuzzy logic o PID loop 2. AC Motor: o Driven by Variable Frequency Drive 3. Mechanical prototype of the bed o Simulates variable velocity capability 4. Joystick controller prototype

Design Plan User Interface Mechanics Analog joystick Bed angle sensor Central Control Serial-to-Digital converter current angle forward/reverse Microcontroller Cruise Control Input speed (Fast, medium, slow) Input desired bed angle (High, medium, low) speed Variable Frequency Drive AC motor

User Interface • Cruise control for large movement o. User defines desired speed angle o. Output is digital • Analog joystick for fine movement o. Output voltage proportional to displacement o. Output is a serial signal Need serial-to-digital converter • Both digital signals can be input and integrated into microcontroller

User Interface • Ergonomics of cruise control buttons o Large o Engraved o Easy to push • Ergonomics of joystick o Elliptical handle allows easy grip o Small force and range of motion required to operate

Design Plan User Interface Mechanics Analog joystick Bed angle sensor Central Control Serial-to-Digital converter current angle forward/reverse Microcontroller Cruise Control Input speed (Fast, medium, slow) Input desired bed angle (High, medium, low) speed Variable Frequency Drive AC motor

Mechanics • Motor shaft - bed screw connector o Aluminum 6061 1. 5” diameter rod stock o Connect to drive shaft with push-pin o Connect to motor with key Motor shaft Bed screw Key Connector

Mechanics • Motor Mount o Low-carbon steel 1” tubing, 1/8” thick o Two parallel bars with a rise of 3" o Welded to bed frame, and bolted to motor

Mechanics • Bed angle sensor One-turn potentiometer: Output voltage depends on bed-back angle

Design Plan User Interface Mechanics Analog joystick Bed angle sensor Central Control Serial-to-Digital converter current angle forward/reverse Microcontroller Cruise Control Input speed (Fast, medium, slow) Input desired bed angle (High, medium, low) speed Variable Frequency Drive AC motor

Central Control • Microcontroller: BASIC Stamp Discovery Kit with USB connection • Integrates signals from joystick, cruise control, and sends them to VFD • Can be programmed in BASIC language Cruise control Desired angle θ 1 Microcontroller Minimize θ 1 - θ 2 Current angle θ 2 Angle sensor Feedback Loop

Patient Safety Considerations • Limit maximum speed • Prevent back from falling during power loss brake system • Controller needs to be electrically insulated • Waterproof controller assembly

Testing • Volunteer and patient human subjects • Test the bed’s performance for: o Comfort o Effectiveness o Intuitiveness o Feedback o Ease of Use • Comply with set regulations when testing the bed o UW-Madison Institutional Review Board § Develop complete protocol § Assess all potential dangers to all subjects o Proper privacy procedures o Informed consent

Milestones • March 30 – Build joystick controller – Install motor on bed • April 15 – Have functional microcontroller – VFD – Motor pathway • April 30 – Testing – Refining design

References Doubler, J. A. , Childress, D. S. An Analysis of Extended Physiological Proprioception as a Prosthesis-Control Technique. Journal of Rehabilitation Research and Development, (21), Issue 1, pp. 5 -18. Simpson, D. C. (1974). The choice of control system for the multimovement prothesis: extended physiological proprioception (EPP). The Control of Upper-Extremity Prostheses and Orthoses. (P. Herberts et al, ed) Springfiled, Illinois, C. C Thomas. pp. 146 -150. Simpson, D. C. (1973). The control and supply of a multimovement externally powered upper limb prosthesis. Proc. 4 th Int. Symp. External Control of Human Extremities, Belgrade, Yugoslav, pp 247 -254. Zadeh L. A. (1968). Fuzzy algorithms. Information and Control, 5, pp. 94 -102

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