Rotary Actuator No-Back Device Prevents Back Drive Torque

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Solution Overview

Problem

Conventional patient support systems face challenges with linear and rotary actuators, including space inefficiency, back driving issues, and lack of stiffness, which compromise the structural integrity and reliability of movable members in patient support apparatuses.

Innovation Solution

The use of a rotary actuator with a planetary gear train and a no-back device that prevents back drive torque, enhancing the structural integrity and reliability by ensuring movement is power-dependent and not load-dependent, and incorporating a roller clutch device for improved torque transmission and prevention of back drive.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If linear actuators are used to move movable members, then the movable members can be moved, but the actuators take up a large and undesirable amount of space

Engineering Contradiction:

Improvespace occupied by actuatorVSAvoidmovability of movable member

Core Design Contradiction:

Volume of moving objectVSEase of operation

Solution Approach 1:

The patent replaces linear actuators with rotary actuators coupled to crank mechanisms. The rotary actuator converts rotational motion to linear motion through the crank, achieving the same functional result with a more space-efficient configuration. This substitution resolves the contradiction by reducing actuator volume while maintaining the ability to move movable members.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Volume of moving object

If rotary actuators are used to move movable members, then the actuators take up less space, but the movable members may back drive and go into undesirable positions

Engineering Contradiction:

Improvespace occupied by actuatorVSAvoidposition stability of movable member

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent incorporates no-back devices that apply preliminary counteracting force to prevent back driving before it occurs. These devices engage to counteract loads that would otherwise cause the movable member to drift to undesirable positions, thereby maintaining position stability while using space-efficient rotary actuators.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent introduces no-back devices as intermediary components between the rotary actuator and the movable member. These intermediaries transmit power during forward motion but block reverse motion, resolving the contradiction by allowing compact actuator design while preventing unwanted back driving through the intermediary mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Volume of moving object

If rotary actuators are used, then space is saved, but the actuators generally lack stiffness to give confidence in structural integrity

Engineering Contradiction:

Improvespace occupied by actuatorVSAvoidstiffness of actuator

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The patent employs composite structural designs combining rotary actuator components with support structures and gear mechanisms. This composite approach creates a stiffer overall system that maintains structural integrity and gives confidence in the actuator's strength while preserving the space-saving benefits of rotary actuation.

Inventive Principle:

Principle #40Composite materials

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution provides a more reliable and efficient patient support system with improved structural integrity and reduced risk of undesirable movements, ensuring safe and predictable operation of movable members.

Implementation Method 1

The gear assembly includes a planetary gear train having an input element and an output element

Methodology Applied

Scientific EffectPlanetary gear mechanism: Epicyclic Gearing

Implementation Method 2

The roller clutch device is coupled to the carrier and is configured to permit movement of the movable member through application of a drive torque and prevent back drive torque applied to the output element from moving the movable member

Methodology Applied

Scientific EffectRoller clutch mechanism: Ratchet

Data Source

PatentUS10765575B2Patient support systems with rotary actuators comprising rotation limiting devices

Publication Date: 2020.09.08 STRYKER CORP

AI summary

A patient support system comprises a patient support apparatus for patients. The patient support apparatus comprises a base and a patient support surface supported by the base. The patient support apparatus also comprises movable members that are movable between at least a first position and a second position. One or more rotary actuators with rotation limiting devices are coupled to each movable member. The actuator with the rotation limiting device permits drive torque to move the movable member in a desired position between the first and second positions and restricts back drive torque from moving the movable member.