Patient support apparatus with actuator feedback
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Solution Overview
Problem
Patient support apparatuses face inaccuracies in actuator position estimation due to analog encoder signals that only indicate motor movement, not actual actuator arm position, leading to discrepancies caused by slippage and noise, which complicates accurate control.
Innovation Solution
Incorporating position switches and a controller that estimates the absolute position of the actuator arm based on motor encoder signals and updates this estimate when the arm triggers the switches, ensuring accurate control by cutting power to the motor when position limits are reached, thus preventing over-extension or over-retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If motor encoder signals are used to estimate actuator arm position, then position feedback is provided, but measurement precision deteriorates due to slippage and noise causing discrepancies between motor movement and actual arm position
Solution Approach 1:
The patent implements a feedback mechanism using position switches that directly sense the actuator arm position and provide correction signals to the controller. When the arm reaches positions corresponding to the switches, the switches generate signals that update the estimated position, thereby correcting accumulated errors from encoder drift and slippage.
Solution Approach 2:
The patent introduces position switches as intermediary elements that indirectly measure the actuator arm position. These switches serve as mediators between the mechanical arm and the control system, providing absolute position references without requiring direct continuous measurement of the arm itself, thus resolving the precision issue while maintaining the encoder-based estimation approach.
2Measurement precision
If position switches are added to update absolute position estimates, then measurement precision improves, but device complexity increases due to additional components
Solution Approach 1:
The patent applies partial action by using position switches only at specific discrete positions of the actuator arm rather than continuous measurement. The switches are positioned to trigger only when the arm reaches certain predetermined locations, providing sufficient position correction without requiring complex continuous measurement systems throughout the entire range of motion.
3Measurement precision
If power is continuously supplied to the motor for precise control, then control precision is maintained, but energy consumption increases
Solution Approach 1:
The patent implements periodic action by supplying power to the motor in discrete intervals rather than continuously. The motor is activated only when position adjustment is needed, and the position switches provide periodic feedback signals that trigger motor activation. This approach maintains control precision by updating position only when necessary while significantly reducing overall energy consumption compared to continuous operation.
Data Source
AI summary
A patient support apparatus—such as a bed, chair, cot, stretcher, or the like—includes a frame, support surface, movable component, an actuator, and a controller. The actuator includes a motor, an encoder, a spindle, an extendable arm, multiple power switches, and a position switch. The controller estimates a position of the extendable arm based on motor encoder signals and updates the position estimate when the arm triggers the position switch. The power switches cut power to the motor without intervention by the controller when the extendable arm triggers either of the power switches. In some embodiments, the motor is a brushless DC motor. In still other embodiments, multiple position switches are adapted to be open in different ranges of position, and the controller determines which range the extendable arm is located in based on the state of the position switches.