Dual-Shaft Rotational Joint Encoder Layout for Precise Speed Sensing

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Solution Overview

Problem

Existing rotational joints in robots and robotic arms face challenges in accurately measuring and adjusting the rotational speed of output shafts, which is crucial for precise control of robotic arm movements.

Innovation Solution

The proposed solution involves a rotational joint design that includes a driving device with an inner and outer shaft, and an encoder module with synchronized disk assemblies and sensor assemblies. The encoder module is mounted on the driving device, with disk surfaces arranged coplanar and radially spaced apart, allowing for independent rotation of the inner and outer shafts and accurate measurement of their rotational speeds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If two sets of magnetic encoder modules are located on both sides of the driving device with disks fixed to output shafts, then the rotational speed of output shafts can be measured, but the measurement precision is insufficient due to interference between the two encoder modules

Engineering Contradiction:

Improverotational speed measurement precisionVSAvoidmagnetic field interference between encoder modules

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

A magnetic shielding plate is introduced as an intermediary component between the first and second encoder modules. This shielding plate blocks magnetic field interference between the two modules, allowing both to operate simultaneously without mutual interference, thereby improving measurement precision while maintaining the dual-sided configuration

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The encoder system is segmented into two independent modules positioned on opposite sides of the driving device. Each module has its own disk fixed to a specific output shaft, allowing independent measurement of rotational speeds while the magnetic shielding plate prevents cross-interference between the segmented modules

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If optical encoders are used to measure rotational speed, then measurement can be achieved, but the reliability is poor due to sensitivity to vibration, pollution and corrosion

Engineering Contradiction:

Improverotational speed measurementVSAvoidresistance to vibration, pollution and corrosion

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces optical encoding mechanisms with magnetic encoding mechanisms. Magnetic encoders use magnetic fields instead of optical paths, making them resistant to vibration, dust, oil, water vapor, and salt spray that plague optical systems. The magnetic disk and magnetic sensor assemblies maintain measurement precision while significantly improving reliability in harsh environments

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If the disk surfaces of first and second disk assemblies are arranged coplanar and radially spaced apart, then the encoder module structure is compact, but the manufacturing precision requirement increases

Engineering Contradiction:

Improveencoder module structure compactnessVSAvoidcoplanar alignment and radial spacing precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The magnetic shielding plate is pre-positioned between the first and second disk assemblies during assembly. This preliminary placement of the shielding plate establishes reference positions that guide the coplanar alignment and radial spacing of the disk surfaces, reducing the actual manufacturing precision requirements while achieving the compact encoder module structure

Inventive Principle:

Principle #10Preliminary action

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 design enables precise control of the robotic arm's movement by accurately measuring and adjusting the rotational speeds of the output shafts, improving the joint's operational efficiency and reliability.

Implementation Method 1

The sensor can be a Hall-effect device, which senses a change in voltage

Methodology Applied

Scientific EffectHall-effect: Hall Effect

Implementation Method 2

or a magnetoresistive device, which senses a change in a magnetic field

Methodology Applied

Scientific EffectMagnetoresistive effect: Magnetoresistance

Data Source

PatentUS20250067302A1Rotational joint and device having same

Publication Date: 2025.02.27 SHANGHAI FLEXIV ROBOTICS TECH CO LTD

AI summary

The present application relates to a rotational joint and a device having the same. The rotational joint includes a joint housing, a driving device mounted in the joint housing, and an encoder module mounted on the driving device. The driving device includes inner shaft and an outer shaft surrounding the inner shaft and radially spaced apart from the inner shaft. The encoder module includes a first disk assembly configured to rotate synchronously with the outer shaft, a second disk assembly configured to rotate synchronously with the inner shaft, a first sensor assembly disposed adjacent to the first disk assembly to detect movement of a disk of the first disk assembly, and a second sensor assembly disposed adjacent to the second disk assembly to detect movement of a disk of the second disk assembly. A disk surface of the first disk assembly and a disk surface of the second disk assembly are arranged to be coplanar and radially spaced apart by at least a predetermined distance. The device includes at least one rotational joint.