Transcript Mid-Semester Presentation 3479 kb Thursday

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:
oLack of usability
No velocity control
oErgonomically 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
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
oUser defines desired speed and angle
oOutput is digital
•Analog joystick for fine movement
oOutput voltage proportional to displacement
oOutput 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 θ1
Microcontroller
Minimize θ1- θ2
Current
angle θ2
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 UpperExtremity 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
Questions?