Elements

Elements

Machine elements like joints, actuators, sensors are the critical parts in every mechanism. They strongly influence the mechanisms characteristics like stiffness, precision or working volume and therefor need very special attention.

The LSRO investigates a lot this domain in order to find new designs and approaches for machine elements.
Some of these are enumerated below:

Spherical Joint

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Parallel kinematics often need joints with higher mobilities like spherical joints. But such joints offering good capabilities are very rare or inexistant on the market and therefore need to be designed for every new machine.

The LSRO developped a spherical joint based on gliding elements that has a considerably high stiffness and does not require a big amount of mounting space. This joint was designed for the HITA STT (see section Kinematics).

Its caracteristics are:

– Stiffness: 500 N/um
– Preload: 2000 N
– Angular stroke: +- 15°

High Stroke Flexible Pivot

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Flexible joints are perfectly adapted to high precision application exept one drawback which is their very limited stroke.
The LSRO therefore made some investigations in the domain of high stroke flexible elements and found an interesting concept for a pivot.

The pivot is composed from 2 single RCM (Remote Center of Motion) pivots with their middle parts movement controlled by a mechanism in order to execute always half of the total stroke of the pivot.

This design leads to the following characteristics: 

– Angular stroke: +- 15°

 

Double Bar System

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The Double Bar System contributed a lot to the success of the Delta robot because of its simplicity and capability to be easily dismantled. It is composed from 2 bars and 4 spherical joints composing a parallelogramm in space. The figure shows only one half of the system.

Several parallel kinematics nowadays use this system and a lot of included elements are standardized and can be bought directly.