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

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

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. Brenton

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. Brenton

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 Brenton

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

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

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

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

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

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

Mechanics Motor shaft Bed screw Key Connector Motor shaft - bed screw connector Aluminum 6061 1.5” diameter rod stock Connect to drive shaft with push-pin Connect to motor with key Motor shaft Katy Bed screw Key Connector

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

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

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

Central Control Minimize θ1- θ2 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 Desired angle θ1 Current angle θ2 Microcontroller Cruise control Angle sensor Minimize θ1- θ2 Feedback Loop Shikha

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

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

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

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. 4th 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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