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

Background: Current Hospital Beds Bed-back can only be operated at one fixed speed Disadvantages: Buttons are hard to push, and inaccessible for some patients Fixed speed  less control and flexibility No feedback to user

Background: Extended Physiological Proprioception (EPP) D.C. Simpson, 1974 Controllers are more intuitive when they act as a natural extension of the user’s body

RERC National Design Competition 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. RERC: Rehabilitation Engineering Research Center

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 a controller based on force-assist concepts, 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

Design Overview MotorController Sensor User Controllable electric frequency Bed-back angle Feedback to controller Feedback to user

Design Overview MotorController Sensor User Controllable electric frequency Feedback to controller Feedback to user Bed-back angle

Motor Control Bed back is controlled by a single-phase AC induction motor Motor speed cannot be controlled by magnitude of input current To control motor speed, modulate input current frequency Input current frequency (Hz) Motor speed (rad/sec)

Design Overview MotorController Sensor User Controllable electric frequency Feedback to controller Feedback to user Bed-back angle

Feedback System Sensor measures angle θ actual Differentiator Inputs to feedback loop Reference angle θ ref Error: ξ = θ actual – θ ref Change in error dξ/dt θ actual

Feedback System (cont.) Alternative 1: PD Loop Alternative 1: PD Loop PD = Proportional-Derivative (PDI loop without integral term) Output = K 1 ξ + K 2 dξ/dt The output of the PD loop is used to minimized the error K 1 determines how fast the error is reduced K 2 determines how smooth the transitions are

Feedback System Alternative 2: Fuzzy Logic Alternative 2: Fuzzy Logic Used when the mathematical basis of the system is uncertain or not needed Inputs and outputs are ranges of values, each given a discrete qualifier (“Slow”, “Medium”, “Fast”). Probability Velocity slowmediumfast

Design Overview MotorController Sensor User Controllable electric frequency Feedback to controller Feedback to user Bed-back angle

User Interface User has the choice of two controls: Cruise control: user specifies angle and velocity Controller for fine angle adjustments User receives feedback on the velocity of motion Vibrations in controller (similar to video game controllers) Resistance on controller Combination of visual and auditory cues.

Design Alternative 1 Substitute a DC motor for the existing AC motor on the bed AC current (from wall) AC/DC converter Current amplitude controller DC motor Advantage Simple Disadvantages DC motors rotate when power is off. Cost PD loop

Design Alternative 2 PD loopAC Motor Analog output Advantages: Accurate Smooth transitions Disadvantage: PD loop requires a complete knowledge of the physics of the system Analog error compensation

Chosen Design Fuzzy loopAC Motor Discrete output Advantages Does not require accurate knowledge of the system Corresponds more intuitively to the human mind Disadvantage Less precise (but not a problem for our purposes) Logical error compensation

Plan for Future Work October-December: Analyze the electrical and mechanical aspects of the bed Build a preliminary prototype based on fuzzy logic Conduct preliminary testing January-May: Build final prototype Test ergonomics, ease of operation and safety on volunteers or patients

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. 4 th Int. Symp. External Control of Human Extremities, Belgrade, Yugoslav, pp Zadeh L.A. (1968). Fuzzy algorithms. Information and Control, 5, pp

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