Actuators form cost-effective micro-tensile tester

One of the significant properties of the SMAC range of linear actuators is the ability to apply a known force while registering position.

One of the significant properties of the SMAC range of linear actuators is the ability to apply a known force while registering position.

And it is this function which raised the possibility of providing a microtensile test station at the Microscopy and Imaging Department of the Dental Institute at King's College London.

Previously the mechanical testing of biomaterials involved driving a crosshead stage comprising a rotary motor and lead-screw, with a load cell interposed between the sample and the stressing device.

The major drawback of this system was the speed limitations during rapid life-cycle fatigue tests and the sensitivity of the load cells which were both expensive and prone to damage during fracture events.

The standard SMAC actuator uses a copper voice coil to provide linear motion and force is generated by applying and controlling a known current through the coil, equally force feedback can be monitored by the same means.

It also incorporates an integrated optical encoder with resolution options ranging from 5 to 0.1um.

This assembly is mounted onto a high specification linear guide and consequently it provides a robust unit capable of both applying and reporting force and position at a fraction of the cost of conventional setups.

SMAC carried out a series of trials at its European Technical office before deciding on a LAL90-015 with a 0.5um linear encoder and driven by a LAC-1 single-axis controller.

This was consequently supplied to KCL through one of SMAC's distributors Linos Photonics.

The system provides a large dynamic range of actuating velocities and forces and is small enough to fit onto a confocal microscope stage.

It has since been used in microtensile, fatigue and fracture toughness testing, and as a micropositioning device.

Identical samples have been tested using both SMAC and conventional stages and the results were directly comparable.

These results were recently displayed at the International Association Dental Research meeting in Gothenburg where KCL's Professor Tim Watson described the SMAC system as: "exhibiting robust construction, great flexibility in application and simple programming and is equally valuable in many other applications such as shear, micro-shear and compressive modes of strength testing".

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