# FLEXURE GUIDING – 2 LEAF SPRINGS IN PARALLEL

## Construction Design & Examples

### INTRODUCTION

A flexure guiding with 2 leaf springs or flexures in parallel are often use as a (quasi-) linear guidance were play must be eliminated. This sheet allows you to design such a construction, how to reinforce it and how to eliminate the parasitic motion.

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###### Pro’s & Con’s

Play/backlash free

Well predictable stiffness (Cx)

Parasitic displacements (uz )

Short stroke

(small) Stiffness in direction of movement

###### Elimination of parasitic displacements

Through a double parallel leaf spring (in series) the parasitic displacement can be eliminated, like:

The drive stiffness (Cx) halves; however the guiding stiffness (Cz) halves as well.

###### Leaf spring configuration

For machinability, often reinforced leaf springs or 2 elastic hinges in series are used as an alternative per leaf spring. If so use the following guide-lines:

Each flexure with then:
(matching movement)
(matching )
(guideline reinforcement)
(matching movement)

(elastic hinge guide line)

###### Motion

dynamic movements: fatigue stress limit
quasi-static movements: yield stress limit ()

###### Over constrained design

Essentially, 2 parallel leaf springs are over constrained. This could be overcome if internal elasticity is introduced like low torsion stiffness of the moving body or notching 1 out of 2 leaf springs. Practically, the best way is to machine the fixed world, the leaf spring and the moving body monolithically.

###### Applying Force Fx

To ensure identical normal force on each leaf spring and thus; a pure linear guidance, the force Fx should be applied at as depicted below.