Helical Torsion Spring Joint for Articulated Arm CMM Rotation Limiting

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Solution Overview

Problem

Manual CMM arms face limitations in joint rotation, particularly with mechanical end stops causing shocks and reducing accuracy, and existing solutions like slip rings are prone to wear and interference.

Innovation Solution

A connection device with a helical torsional spring assembly and stop pins on each segment limits rotation smoothly, absorbing torque to prevent shocks and maintain accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If mechanical end stops are used to limit joint rotation, then the rotation is limited, but shocks and collisions occur reducing accuracy

Engineering Contradiction:

Improverotation limitationVSAvoidmeasurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies beforehand cushioning by introducing a spring mechanism between the two segments that compresses gradually as the joint approaches its rotation limit. This spring absorbs the kinetic energy and prevents the harsh collision that would occur with rigid mechanical end stops, thereby maintaining measurement accuracy while still limiting rotation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The spring acts as an intermediary element between the two segments. Instead of direct mechanical contact between end stops causing shocks, the spring mediates the interaction by providing a compliant force that gradually increases with compression, smoothing out the transition and eliminating harmful collisions.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If slip rings are used for unlimited rotation joints, then electrical signals and power are transmitted, but wear and interference occur reducing quality

Engineering Contradiction:

Improverotation capabilityVSAvoidsignal quality

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent replaces the mechanical slip ring system with a cable-based electrical transmission system. Cables are used instead of mechanical contacts, eliminating wear and interference issues associated with slip rings while maintaining the ability to transmit electrical signals and power through the rotating joint.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If multiple rotation rings are used to achieve rotation higher than 360°, then the rotation angle increases, but the complexity of the device increases

Engineering Contradiction:

Improverotation angleVSAvoidjoint structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies dynamics by using a spring mechanism that dynamically adapts to the rotation angle. The spring can accommodate multiple rotations (beyond 360°) by compressing and extending as the joint rotates, providing a flexible solution that avoids the need for complex multi-ring mechanical structures while achieving the desired extended rotation capability.

Inventive Principle:

Principle #15Dynamics

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 effectively limits rotation without causing shocks, enhancing accuracy and reducing wear, while allowing multiple rotations without mechanical end stop collisions.

Implementation Method 1

a spring assembly comprising one or more helical torsion springs, which assembly has a first end and a second end, configured for placement co-axially along the joint axis of rotation

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

such that the degree of rotation by the one segment about the joint axis relative to the other segment is limited when spring assembly engages both pins and by the torque induced in the spring assembly

Methodology Applied

Scientific EffectTorque: Torque

Data Source

PatentUS7765707B2Connection device for articulated arm measuring machines

Publication Date: 2010.08.03 3D SCANNERS LTD

AI summary

The present invention concerns a connection device for use in an articulated apparatus comprising two or more tandemly arranged interconnected movable segments, for limiting rotation between two adjoining segments connected by a joint having a single axis of rotation, comprising: a spring assembly comprising one or more helical torsion springs, which assembly has a first end and a second end, configured for placement co-axially along the joint axis of rotation; a stop pin adapted for attachment to one adjoining segment, another stop pin adapted for attachment to the other adjoining segment, each pin moveable around the axis of rotation in fixed relation to the attached segment, wherein the first end of the spring assembly is configured for disengageable connection with the stop pin of one segment, and the second end is configured for disengageable connection with the stop pin of the other segment, such that the degree of rotation by the one segment about the joint axis relative to the other segment is limited as spring assembly engages both pins, and by the torque induced in the spring assembly.