Development of Micro Hardness and Stiffness Testing System by Micro Robot for Biomaterials

Montree Pakkratokea, SMG. Iroshanab, Chisato Kanamoric and Hisayuki Aoyamad

Department of Mechanical Engineering and intelligent systems, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan.


The development of small force generator mechanism with voice coil actuator and piezo driven micro robot for surface hardness and stiffness investigation is described. This tiny force generator is composed of voice coil actuator and tandem leaf spring mechanism. The small force can be controlled by electrical current which is supplied to coil and positioned precisely at the balance point with the parallel leaf spring with no mechanical friction. And the full bridge strain gauges on both side of double leaf spring can detect the small force which is applied to the micro indenter. This unique layout can provide a small force up to 20mN with good linearity and 0.05mN resolution. The displacement of the indenter head can be measured by the laser displacement sensor for monitoring the depth behaviour of the indenter during whole dwell time. Since the overall size of this force generator is compact enough to implement on the piezo driven micro robot, it can be possible to employ them in such the SEM chamber for in-situ measurement. In the primary experiment, after the performance of micro hardness sensing is compared with the hardness standard block to certify its ability, the sensing head is arranged to measure the sample that is set on the piezo driven inch-worm micro robot. This micro robot can move the sample precisely step by step with 1 μm per step on metal plate so that the sample can be scanned with microscopic resolution. In the experiment results, the elasticity investigations with various bio samples such as human nails and rice grains are successfully checked by the indentation load-depth curve.

Keywords: Voice coil actuator, Tandem leaf spring mechanism, Strain gauge, Inchworm micro robot, Micro indenter.

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