3-DOF Robot Joint Mechanism for Human-Like Torsion Motion

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Solution Overview

Problem

Conventional humanoid robots with two rotational degrees of freedom at joints cannot perform torsional motions, limiting their ability to mimic human-like movements, and existing three-rotational-degree-of-freedom mechanisms are complex and restrictive in motion.

Innovation Solution

A three-rotational-degree-of-freedom connection mechanism featuring three actuators with variable length links and link attaching units, allowing for rotational freedom around a torsion axis and enabling compact, powerful joints without motion restrictions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a conventional two-rotational-degree-of-freedom joint is used, then the joint structure is simple, but the robot cannot perform torsional motions and cannot mimic human-like movements

Engineering Contradiction:

Improvemotion capabilityVSAvoidjoint structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The joint is divided into three independent rotational degree of freedom components (two rotational DOF joint and one torsion axis), allowing each component to be controlled separately by dedicated actuators, thereby achieving complex human-like motions including torsion while maintaining modular structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The three-rotational-degree-of-freedom joint structure enables the wrist to perform multiple functions including rotation, elevation/depression, and torsion, making it capable of mimicking various human wrist motions that a two-DOF joint cannot achieve

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If an existing three-rotational-degree-of-freedom mechanism is used, then the robot can perform torsional motions, but the structure becomes complicated and the ankle and wrist cannot be made thick

Engineering Contradiction:

Improvetorsion capabilityVSAvoidjoint structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The mechanism is segmented into independent rotational DOF components with separate actuators, avoiding the need for complex integrated mechanisms while achieving three-rotational-degree-of-freedom functionality

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of adding complex mechanisms to achieve torsion, the patent inverts the approach by using three variable length links connected to three actuators, where the actuators directly control the link lengths to produce rotational motions including torsion around a fixed axis

Inventive Principle:

Principle #13The other way round (Inversion)

3Shape

If the ankle and wrist are made thin to achieve human-like shape, then the aesthetic requirement is met, but the distance between the joint fulcrum and link connection point is short, reducing power output

Engineering Contradiction:

Improvehuman-like appearanceVSAvoidjoint power output

Core Design Contradiction:

ShapeVSPower

Solution Approach 1:

The patent moves the actuators from the joint location to the link, utilizing the length dimension of the link to accommodate actuator placement. This allows the joint to remain thin and compact while the actuators are positioned along the link where space is available, thereby maintaining both human-like appearance and sufficient power output

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Volume of moving object

If the parallel link mechanism is used, then the structure is compact, but the variable length links cannot be rotated around the fixed length link, creating motion restrictions

Engineering Contradiction:

Improvejoint compactnessVSAvoidmotion freedom

Core Design Contradiction:

Volume of moving objectVSAdaptability or versatility

Solution Approach 1:

Instead of constraining the variable length links to remain parallel to a fixed length link, the patent inverts the approach by allowing the variable length links to rotate freely around each other and around a fixed axis, with the actuators controlling link lengths to achieve desired positions without parallelism constraints

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS11571806B2Three-rotational-degree-of-freedom connection mechanism, robot, robot arm, and robot hand

Publication Date: 2023.02.07 MITSUBISHI ELECTRIC CORP

AI summary

A three-rotational-degree-of-freedom connection mechanism required for a robot that can make motion similar to a human has a simple structure, and there is no restriction on motion within a movable range. The three-rotational-degree-of-freedom connection mechanism includes a joint connecting a second member rotatably to a first member with three rotational degrees of freedom including rotation around a torsion axis, three actuators each including variable length links having a variable length, and power sources for generating force changing the lengths of variable length links and three first-member-side link attaching units provided in first member and the second-member-side link attaching units provided on the second member such that variable length links having a twisted relationship with respect to a torsion axis exist in each state within a movable range of joint.