Surf-I, a device for monitoring washboard

The basic measuring principles in the Surf-i Monitoring System use latest development in Vision Technology together with a specially developed algorithm for image analyses.

Figure 1. Washboard definitions.

The Surf-i is an off-line device consisting of a measuring head and a computer. When moving the measuring head for 10 seconds over the desired area approximately 1000 separate characteristics of valleys and the corresponding wavelengths are recorded. In Figure 1. it is illustrated how we define depth of valley (d) and wavelength (λ). In order to eliminate the influence of the roughness of the liner a special algorithm is used to obtain a smooth curve (white curve) from the separate readings (red points). (Notice the very high spatial resolution, i.e. the accuracy in the individual determinations of the surface structure is in the order of a few microns.)

Figure 2. Board Samples.

Measurements on two different boards (Fig. 2.) are used to demonstrate the functionality of Surf-i. The results are presented as histograms that show the proportion, or frequency, of readings that fall into each of several categories or bins. The categories are valley depth, or washboard, and wavelength, respectively. Histogram is frequently used as a basic tool for quality control.

Sample A shows a concentration of depths between 100 and 150 microns (Fig. 3.) and that the wavelength centers around 6 mm (Fig. 4.). The surface of sample B is much smoother, as seen from Figure 2., and is clearly verified in Figure 5. where the depths varies in a region which is one fourth of sample A.


Figure 3: Washboard Sample A


Figure 4: Wavelength Sample A

From Figure 6. it is also noticed, that beside the predominant wavelength there exists others, both shorter and longer. The reason for this can be found in the fact than the very small dents found (in an order of magnitude of a few fiber thicknesses) also may emanate from “local buckling” or “cockles”.


Figure 5: Washboard Sample B


Figure 6: Wavelength Sample B

If we apply a conservative approach to washboard it refers to the undulating topography coinciding with the fluting tips and valleys of the corrugated board and that causes striping in the printed board. An obvious alternative is to only present the distribution of depths belonging to the wavelength of the medium. The most straight forward way is to give mean values and standard deviation. A number of other alternatives can also be offered, including limits for approved quality.