Electroactive Polymer Actuator Polarity Inversion

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Solution Overview

Problem

EAP-based actuators experience non-constant actuation over time and changes in the drive versus actuation curve during subsequent actuation periods, hindering their practical application, especially in prolonged or frequent use scenarios.

Innovation Solution

Employing periodic inversion of the polarity of the driving signal within a single actuation event or across multiple events, maintaining the same electric field strength over different polarity periods to reduce interfering processes and maintain actuation direction independence from voltage polarity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If EAP actuators are used for prolonged and/or frequent actuation periods, then the actuation capability is maintained, but the actuation becomes non-constant over time and the drive versus actuation curve changes

Engineering Contradiction:

Improveprolonged actuation periodVSAvoidactuation constancy

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The patent applies periodic inversion of the voltage polarity during actuation cycles. The driving voltage alternates between positive and negative polarities in a periodic manner, which prevents charge accumulation and maintains constant actuation characteristics over prolonged periods. This periodic polarity inversion resolves the technical contradiction by enabling long-duration operation while maintaining actuation reliability and consistency.

Inventive Principle:

Principle #19Periodic action

2Force

If high electric field strength is applied to achieve sufficient actuation, then the actuation stress and strain are improved, but interfering processes such as charge transportation and polymer relaxation occur

Engineering Contradiction:

Improveactuation stressVSAvoidcharge transportation and polymer relaxation

Core Design Contradiction:

ForceVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of charge accumulation into a beneficial effect by utilizing polarity inversion. The alternating polarity causes charges to oscillate back and forth rather than accumulating unidirectionally, which actually enhances actuation performance while preventing the harmful effects of charge transportation and polymer relaxation that occur with unidirectional high-field application.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If voltage polarity is inverted periodically, then charge build-up and interfering processes are reduced, but the actuation direction must remain independent of voltage polarity

Engineering Contradiction:

Improveactuation stabilityVSAvoidactuation direction independence

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent employs a composite structure consisting of an electroactive polymer layer sandwiched between two electrode layers. This composite configuration ensures that the actuation direction is determined by the polymer's intrinsic properties and structural arrangement rather than voltage polarity. The symmetric placement of electrodes and the specific orientation of the EAP layer create a system where actuation occurs in a consistent direction regardless of whether the applied voltage is positive or negative, thus resolving the contradiction between reliability through polarity inversion and adaptability through direction independence.

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

This approach reduces the effects of charge and dipolar motion, polymer relaxation, and electrical breakdown, leading to more stable and prolonged actuation performance without compromising the actuation capability.

Implementation Method 1

In actuator devices of which the actuation is based on electrical stimulation of electroactive polymer (EAPs), the actuation is caused by a change in size and/or shape of the EAP material when such stimulation takes place.

Methodology Applied

Scientific EffectElectroactive polymer actuation: Electroactive Polymer

Implementation Method 2

While in FIG. 1 this leads to symmetrical deformation in the form of expansion in the indicated directions accompanied by layer thinning (lateral expansion with thinning) of the EAP layer due to the layer being freely suspended

Methodology Applied

Scientific EffectDielectric elastomer contraction: Electrostriction

Data Source

PatentUS11251357B2Actuator device based on an electroactive polymer

Publication Date: 2022.02.15 KONINKLIJKE PHILIPS NV

AI summary

An actuator device (21) comprises an electroactive polymer (EAP) and a driver (20) for generating a electrical drive signals which give opposite polarity voltages and thus electrical field within the electroactive polymer at different times. In this way, charge build-up can be reduced or avoided, while prolonged activation times are still possible. This improves the performance and/or lifetime of the device.