After completing the set up of the system and selecting the desired settings in accordance with the details in the User's Manual, the user places the sensor probe over the sample material to be measured, as shown in the image at right, and begins measurements via the Biosensor's Windows compatible software. A small motor located in the upper end of the probe shaft is activated by the computer, which controls the depression. The sensor tip pushes down on the material once and retracts. The user should perform several practice measurements to become familiar with the amount of depression that is appropriate to use without harming the material. 200 tactile, pressure and depression data per second are swiftly and sequentially processed and recorded by the computer in real time.

Data Display and Interpretation

The tactile reading is expressed in Hz and is given as Df. Pressure and depression values are given as grams and millimeters, respectively.  The thumbnail image shows the computer display of data from all three sensors as the material is measured. (The regular size image is dimensionally large and 83 kb.)

The vertical axis of the left-side graph represents each parameter (Df, depression, and pressure) and the horizontal axis shows time.  The user can use this graph to determine if the measurement is being performed well and consistently.  The softer the material is, the more negative Df becomes and the lower the blue (tactile) curve will dip.

The right-side graph represents the hysteresis curve (further explained below). The user can choose from a variety of hysteresis curves by selecting the preferred parameter in the menu boxes at the top. They are currently set as X: Pressure and Y: Tactile. Thus, the current display shows tactile stiffness as Df on the vertical axis versus pressure on the horizontal axis. Note that when tactile is selected, as on the y-axis of this image, that Df is scaled in a negative direction. This enables easier viewing.

The lower portion of the screen displays the raw data and is arranged sequentially with the second, third and fourth columns consisting of the tactile, pressure, and depression measurements, respectively.  The user may wish to use these data for further analysis via software such as Excel.

Hysteresis Curves

Hysteresis curves, such as the ones in the image at right, will be displayed in the upper right portion of the Venustron software. A hysteresis curve is composed of two parts, a bottom and a top, which are formed when the sensor pushes down (bottom) and then retracts (top), as shown by the arrows. The distance or area between the two parts depends on the visco-elasticity of the material being measured.  As the sensor is pushing down on the material, it encounters a "full resistance" from that material, but as the sensor retracts the "resistance" is dampened because the material takes time to regain its former shape. This time depends on how "fluid" the material is. Thus, a shorter distance between the two parts corresponds with a more elastic material, while a wider distance represents less elasticity.

When comparing tactile and pressure data as in the above graph, a more leftward, or upward, tilt of this curve indicates a softer substance (as Df becomes more negative).  Also, at the very beginning of the lower curve (the one in red), a "flat" spot can be seen.  This is indicative of a relatively hard surface, the area first contacted by the sensor.

If the Venustron system is used to measure sample materials that are not consistent but rather are thick and made up of different layers, such as skin and the underlying muscle, then the hysteresis curve can be used to view the material's characteristics at different layers. The first portion of the curve describes the first layer while the next portion describes the next layer and so on. Where one portion ends and the next begins and how deep the sensor is actually measuring must be researched in order to be determined.

Sample Data

The following graphs display data from measurements performed in research concerning the visco-elasticity of skin and muscle. (See the list of research publications, Motooka 1997) The auto-press (Venustron) was first applied to silicone gum to investigate its basic performance. The distance moved by the sensor probe, 3 mm, is controlled by the pulse motor, and as the sensor element contacts the silicone gum, the change in frequency, the contact pressure, and the displacement are swiftly and sequentially processed by the computer. The change in frequency is proportional to the hardness of silicone gum. The results demonstrate that, since the hysteresis curves depend on the visco-elastic properties of silicone gum, we can analyze qualitatively the hardness and/or softness of soft tissue using the instrument.

The next two graphs show the effect of cosmetic treatment on the skin elasticity of a woman's arm in a 22-years old. In these experiments, after washing and air-drying the skin surface we applied water and lotion respectively (1 ml) onto the skin surface. After about 1 minute of application, we absorbed them with blotting paper at a constant pressure, and then we measured the skin elasticity using the instrument. The results demonstrate that, after treatment with lotion, the skin plasticity increases suddenly and thereafter decreases slowly with time. The water also increases the skin plasticity, but the effects of lotion on the skin elasticity [are] greater than that of water.