Roughness Patent

Background of the Invention:

        

Field of the invention

         

The present invention relates to optical remote devices for measuring one-dimension roughness, which uses the effect of light reflection from a surface.

         

These devices allow the measurements of roughness automatically with the use of a computer.

          

Description of the prior art

          

There are two basic methods to measure the roughness of a surface, optically and mechanically.

              

Mechanical methods are based on the principle of profilometers.  These are very expensive and unstable devices.  The main disadvantage of these devices is the contact with the surface, which could scratch the surface and the device could give inaccurate readings of the roughness measurement.

           

The present invention consists of two simple principles, which are used to measure roughness.  Realization of these methods is inexpensive and does not require any high precision  and sophisticated mechanical and optical applications. The use of a computer allows  fast and easy measurements. Due to its simplicity, this product can also be used to measure roughness in continuous production processes.

          

Abstract:

       

Summary of the Inventions:

                 

These present inventions represent optical devices for remote measurement of one-dimension roughness. These devices allow the measurement of the roughness automatically with the use of a computer.

          

The first method for the measurement:

            

The interference on dimension pattern is formed on the rough surface. The direction of a roughness coincides with the direction of the interference pattern. If the bandwidth in the interference pattern is equal to the period of the roughness, then the light reflected from a rough surface has maximum or minimum intensity. By changing bandwidth in interference pattern and synchronously measuring intensity of the light reflected from a rough surface, it is possible to obtain the information about bandwidth in the interference pattern when the signal has a maximum or minimum intensity.

        

The second method for the measurement:

            

The light from a point source goes on a rough surface and is reflected by it. Reflected light has defined distribution depending on the roughness size. To measure the roughness size it is necessary to compare intensities of reflected light in specular direction and any additional direction.

           

Specifications:

        

Brief description of the Drawings:

          

Figure 1 is the schematic view of the measurement principle. The view includes the  following elements:

         

1 - light beam # 1 with wavelength (lamda)

2 - light beam # 2 with wavelength (lamda)

3 - interference pattern from beam #1 and beam # 2 with bandwidth b

4 - a rough surface with roughness period t

5 - light reflected from a rough surface

           

Figure 2 is the schematic view of a roughness measurement device. The view includes the following elements:

         

1 - a light source which produces beam with wavelength (lamda)

2 - a beam splitter which produces two beams from one

3a, 3b - a moving mirrors which set distance D between beams

4 - an objective which focuses two beams into its focus to produce interference pattern

5 - a rough surface with roughness period t

6 - an objective which collects reflected light on photo-detector

7 - a  photo-detector

8 - a computer

          

Figure 3 is the schematic view of the measurement principle. The view includes the  following elements:

         

1 - a point light source

2 - a rough surface

3 - light reflected from a rough surface

4a - specular direction of analysis of the light intensity

4a - additional direction of analysis of the light intensity

           

Figure 4 is the schematic view of a roughness measurement device. The view includes the following elements:

           

1 - a light source

2 - a rough surface

3a - a photo-detector

3b - a photo-detector

4 - a computer

 

Figure 5:

      

1.1 - Light emitting diode

1.2 - Light emitting diode, 90 degrees phased

2.1 - Photo-detector for reflective component from the surface from 1.1

2.2 - Photo-detector for reflective component from the surface from 1.2

3 - Photo-detector for scattered component from the surface from 1.1 and 1.2

4 - Rough Surface

          

Detailed description of the preferred embodiments:

        

The measurement principle of the present invention will now be described with reference to figure 1.

          

Beam # 1 and beam # 2 produce the interference pattern 3.

Bandwidth b of the interference pattern depends on the angle between beams (epsilon) and the wavelength of light (lamda). Interference pattern 3 has the bandwidth b equal to :

        

    where :

          

(epsilon) - angle between beams,

(lamda) - wavelength of the radiation.

        

If the bandwidth b in the interference pattern is equal to the period t of the roughness, then the light reflected from a rough surface 4 has maximum or minimum intensity. By changing bandwidth b in the interference pattern and synchronously collecting signal from a photo detector 7 with the use of a computer 8, it is possible to obtain the information about bandwidth b in the interference pattern when the signal has a maximum or minimum intensity.

           

Embodiments of the present invention will now be described with reference to figure 2.

          

The primary beam with wavelength (lamda) from a light source 1 goes through a beam splitter 2. Beam splitter 2 divides primary beam in two beams, which are in the same plane and have opposite directions. After a beam splitter 2 beams go to moving reflecting surfaces 3a and 3b. Reflecting surfaces 3a and 3b move and change the distance D between beams. Objective 4 focuses beams into its focus so they produce interference pattern. Bandwidth b of the interference pattern depends on the focal length of objective F, the distance between beams D and the light wavelength (lamda). Interference pattern 3 has the bandwidth b equal to

         

     , where :

          

F - focal length of objective 4,

D - distance between beams,

(lamda) - wavelength of  the radiation.

       

Rough surface 5 is placed into the interference pattern. Direction of a roughness coincides to the direction of the interference pattern. An objective 6 and an objective 4 collect light reflected from a rough surface 5 to a photo-detector 7. Signal from photo-detector 7 goes to a computer 8. Computer 8 collects signal data during measurement and finds the roughness of surface 5.

           

The measurement principle of the present invention will now be described with reference to figure 3.

              

Light from point source 1 is reflected from rough surface 2. Spatial distribution of the light reflected from rough surface 2 depends on the roughness size. If a surface 2 is not rough, the light intensity in specular direction 4a is maximum and the light intensity in any additional direction 4b is zero. If a surface 2 is absolutely rough, then light intensities in both direction 4a and direction 4b are equal to each other. To obtain size of a roughness it is necessary to compare intensities of reflected light in specular direction 4a and in any additional direction 4b.

             

Embodiments of the present invention will now be described with reference to figure 4.

               

Light from a source 1 goes on a rough surface 2. Rough surface 2 reflects incident light. Photo-detector 3a is placed in specular direction of reflectance. Photo-detector 3b is placed in additional direction. Computer 5 compares signals from photodetectors 3a and 3b  calculates the size of a roughness.

            

Claims:

            

1 -  One-dimension roughness can be measured using a one-dimension interference pattern, when the bandwidth of an interference pattern is equal to the period of a roughness. If the bandwidth of an interference pattern is equal to the period of a roughness, then light reflected from a rough surface has maximum or minimum intensity.

           

2. -   Average roughness can be measured by adding an additional light source and a photo sensitive element 90 degrees phased to the one for one dimensional roughness. In this case the incident on the surface comes from 2 direction 90 degrees phased and the additional photo sensitive element allows to average the 2 reflective values for calculate the total average roughness. ( Fig 5 )

                 

Figure 1:

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Figure 4:
Figure 5: