Spring-Mass Legged Robot Energy Regulation

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Solution Overview

Problem

Existing robots face challenges in transitioning between swing and stance phases during legged locomotion, particularly on uneven terrain, due to differences in physics models between flight and ground states, leading to instability and energy inefficiency.

Innovation Solution

A control strategy for spring-mass legged robots that utilizes passive dynamics for energy economy, incorporating leg springs to store and recover energy, and a controller that maintains consistent leg control before and after ground impact, minimizing active force control and ensuring robustness to disturbances by scaling leg extension with forward velocity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If passive dynamics are used for energy economy, then energy efficiency is improved, but stability deteriorates due to falls in the presence of small disturbances

Engineering Contradiction:

Improveenergy efficiencyVSAvoidstability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent implements feedback control by using sensors to detect ground contact events and leg states, then adjusting actuator commands in real-time. The controller monitors the spring-mass system's state and provides corrective actuation to maintain stability while preserving passive dynamics energy efficiency. This feedback mechanism allows the system to recover from disturbances without abandoning passive dynamics.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces an intermediary control system that mediates between passive dynamics and active stabilization. The controller acts as an intermediary layer that only activates when needed (during disturbances or transitions), allowing passive dynamics to dominate during normal operation for energy efficiency while providing active stabilization when required for reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If active force control is used to compensate for disturbances, then stability is improved, but energy economy deteriorates

Engineering Contradiction:

ImprovestabilityVSAvoidenergy economy

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies partial active control rather than continuous active force control. The system uses passive dynamics for the majority of operation (energy efficient) and applies active control only partially - specifically during ground contact transitions and when disturbances are detected. This selective application of active control maintains stability without the continuous energy cost of full active force control.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If leg angle control is adjusted to prevent falls, then stability is improved, but controller complexity increases due to tuning requirements

Engineering Contradiction:

ImprovestabilityVSAvoidcontroller complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent uses parameter changes in the spring-mass system (spring stiffness, mass distribution, leg length) to inherently improve stability margins. By carefully selecting these physical parameters, the system achieves robust passive dynamics that are less sensitive to control imperfections, thereby reducing controller complexity while maintaining stability.

Inventive Principle:

Principle #35Parameter changes

4Reliability

If compliance is used to isolate toe impact, then robustness to disturbances is improved, but energy dissipation increases

Engineering Contradiction:

Improverobustness to disturbancesVSAvoidenergy dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent employs compliance (spring elements) as beforehand cushioning at the toe impact point. The spring absorbs impact energy during ground contact, protecting the system from harsh disturbances. The energy dissipation is managed by selecting spring parameters that provide adequate cushioning while minimizing permanent energy loss, and the spring also stores energy for recovery during the stance phase.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 enables stable and energy-efficient legged locomotion on uneven surfaces by using passive dynamics to absorb and recover energy, maintaining stability without active force control, and ensuring consistent leg control transitions, thus enhancing robustness and reducing energy losses.

Implementation Method 1

at least one leg spring disposed in series between the leg motors and the leg, the spring configured to store energy in the spring during a touchdown part of a stance and configured to recover the stored energy during a liftoff part of the stance

Methodology Applied

Scientific EffectElastic energy storage and release: Spring

Implementation Method 2

compliance isolates the toe impact with the ground from significant mass in actuators, transmissions, or robot leg or body components

Methodology Applied

Scientific EffectCompliance isolation: Damping

Data Source

PatentUS9789920B2Apparatus and method for energy regulation and leg control for spring-mass walking machine

Publication Date: 2017.10.17 THE STATE OF OREGON ACTING BY & THROUGH THE OREGON STATE BOARD OF HIGHER EDUCATION ON BEHALF OF OREGON STATE UNIV

AI summary

A robot for legged locomotion incorporating passive dynamics with touchdown and takeoff control and method.