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University of Wisconsin - Madison Biomedical Engineering Design Courses
INTELLECTUAL PROPERTY STATEMENT
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2. 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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

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

14. 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

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

16. 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

17. 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

18. 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

19. 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

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

21. 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
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
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
Zadeh L.A. (1968). Fuzzy algorithms. Information and Control, 5, pp

22. Questions?