Experimental Study of Hardness Measurement affected by a Cushion between Probe and PTF Pressure sensor
Abstract
In this paper, experimental study of hardness measurement process affected by a cushion between the probe and PTF (polymer thick film) pressure sensor was discussed. Hardness sensing for soft material has been one of the important problems in many fields such as foods industry and material science. One difficulty is how to measure the weak contacting force (0.1 to few N)stable with the small target deformation by low-cost force sensor such as PTF, and we found the result of the measurement stability depending on a cushion between the probe and PTF sensor. The result shows that (1) the output force value depends on the kind of cushion material (plastic, urethane, rubber, styrene elastomer, etc.), (2) the force value was affected by the sensor probe angle to the target material. This result would be useful to develop and study the hardness sensing process intending to reduce the target deformation.
Keywords
Download Options
Introduction
In this paper, hardness measurement process affected by a cushion between the probe and PTF (polymer thick film) type pressure sensor was discussed. Hardness sensing especially for soft material is one of important problem in many fields such as foods industry and material science, including robotics [1-11].For application, the hardness sensing used many fields such as breast cancer diagnosis [6, 12], tension-type headache from the musculoskeletal complaints [13, 14], trapezius muscle hardness changes from the reason of visual display terminal height [15], muscle hardness measurements using ultrasound [16, 17], hardness sensing using optical (IR frequency) techniques [18].As the force sensor, gauge sensor has been used for the hardness measurement. Since gauge sensor measures a distortion of metal, the accuracy of weak force range (0.1 to few N) inevitably drops, and it is considered difficult to measure the hardness of soft material [3,19-28]. PTF sensor, on the other hand, is designed for weak force range (about 0.1 to 20 N), but the high reliability could not be realized by the instability of the contact area change of the two membranes inside the sensor (Fig. 1a).For example, if the shape of the probe contact terminal to the PTF sensor surface (A) is square, the sensor would be pushed by the linear edge (B) of the probe contact terminal (Fig. 1b), and the probe pushing contact area of the membrane is difficult to change linearly by the pushing force. Since the force is measured proportionally the contact area of the two membranes, the shape and contact area change stability of the probe contact terminal is important factor.
Conclusion
In this study, experimental study of hardness measurement process affected by a cushion between the probe contact terminal and PTF pressure sensor was discussed. The result of experiment 1 shows that the material kind of the cushion is important for the stable measurement of the force. Shock-absorbing gel (Gel1, Gel2) was effectively work for transmitting the pushing force to the PTF sensor surface. The result of experiment 2 shows that the pushing angle of the sensor probe was affected to the force measurement and the divergence of the force could be suppressed by using shock absorbing gel (Gel1, Gel2). This result would be useful for developing a low-cost hardness measurement system for soft material.