GB2177793A

GB2177793A - Reflected light surface roughness analyser

Info

Publication number: GB2177793A
Application number: GB08615726A
Authority: GB
Inventors: Yoshizo Honda; Tokuko Oki
Original assignee: Ando Electric Co Ltd
Current assignee: Ando Electric Co Ltd
Priority date: 1985-06-28
Filing date: 1986-06-27
Publication date: 1987-01-28
Anticipated expiration: 2006-06-27
Also published as: DE3621567A1; GB8901427D0; GB2211712B; GB2211711B; GB2177793B; GB2211711A; GB8901426D0; GB2211712A; GB8615726D0

Abstract

A surface roughness analyzer directs a beam of light from a source (1) to an object (4) whose surface roughness is to be measured. A modulator (5) modulates a light source (1) with a modulating frequency. Mirror reflected light is detected by a detector (2) and scattered light by a detector (3). Filters (6, 7) are connected to the outputs of the respective detectors (2, 3) to take out only the component of light at the modulating frequency. The outputs from the filters (6, 7) are not affected by the influence of incoming light other than light from the source (1) and the surface roughness of the object (4) can be accurately measured. Other embodiments describe quadrant detectors to assist in monitoring correct alignment of the apparatus, surface and arrangement in which the scattered light is collected over an annular volume so that the result is not sensitive to directional irregularities on the surface. <IMAGE>

Description

SPECIFICATION Reflected light type surface roughness analyzer BACKGROUND OF THE INVENTION This invention relates to a surface roughness analyzer which directs a beam of light from a given source to an object whose surface roughness is to be measured, detects the both rays of light mirror reflected and scattered from the surface, and determines the surface roughness of the object.

Conventional instruments that depend on reflected light for the measurement of surface roughness project a beam of light from a source to the object to be measured, detect the light reflected from it, snd then determine its surface roughness.

As parameters for the measurement, the intensity of the mirror reflected light and the intensity of the scattered light in a certain direction of reflection are found, and these values are compared to determine the roughness of the object surface.

A typical arrangement for the conventional measurement is schematically represented in FIG. 1.

In FIG. 1 the numeral 1 indicates a light source, 2 and 3 a pair of detectors, and 4 an object whose surface roughness is to be measured.

As shown, a beam of light from the source 1 is directed to the object 4 at an angle of incidence 6, and the light specularly reflected from the surface is thrown back at an angle of reflection 6. The detector 2 captures this mirror reflected light at the angle of reflection 6.

The object 4 causes the light to scatter according to its surface roughness, producing scattered light in addition to the mirror reflected light.

The detector 3 is intended to detect the scattered light at a specific angle of reflection other than that of the mirror reflected light.

The arrangement shown in FIG. 1 presents a problem when conditions are such that natural light, room illumination light, or some light other than from the above light source falls on the object 4; this can make an exact measurement impossible. The attempt to find the ratio of the output of the detector 2 to that of the detector 3 will fail because the incoming light other than from the normal light source is detected as output too, and the ambient bright ness will thus distort the measurement.

Another problem that arises from the conventional instrument of FIG. 1 is that the detection outputs from the detectors 2 and 3 are variable with changes in the angle of inci dence 0 upon the object 4 of the light from the source 1. As a result, the same point of the object can give different data when measured with light at different angles of incidence.

In order to settle these problems, it is necessary to adjust the relative position of the object 4, light source 1, and detector 2 so that when the beam of light from the source 1 strikes the object 4 the detector 2 can detect the mirror reflected light.

The surface of the object 4, for example, a workpiece being machined, usually has streaks of surface irregularities formed in the machining direction. If a beam of light from a light source is thrown onto the object 4 with such surface, the reflected scattered light from the surface will spread in the direction normal to the direction of the streaky surface irregularities.

If the distribution of the reflected scattered light as illustrated in FIG. 2 is determined with the surface roughness analyzer of FIG. 1, the intensity of the scattered light as found by the detector 3 will vary with the direction of the streaky irregularities. This is another problem to be solved.

FIG. 3 shows the pattern of scattered light in the case of FIG. 2, indicating how differently the detection is made by the detector 3 in varied positions.

If such a problem is to be precluded, an arrangement must be made so that, when the light from the source 1 is incident upon the object 4, the mirror reflected light be detected by the detector 2 and the scattered light be infallibly detected regardless of the surface irregularities or the position of the detector 3.

Still another problem associated with the conventional arrangement shown in FIG. 1 is that, because the distance between the detectors 2 and 3 is fixed, a change in the distance between the detector 2 and the object 4 will render it impossible for the detector 3 to detect the scattered light at a certain scattering angle from the object.

The consequence of a change in the distance between the detectors 2, 3 and the object 4 will now be more concretely explained in connection with FIG. 4.

Referring to FIG. 4, the symbol L1 stands for the distance between the detectors 2 and 3, and L2 and L3 the distance each between the detector 2 and the object 4.

In the case of FIG. 4, L3 > L2, and the relation between the scattering angle 62 when the distance is L2 and the scattering angle 63 when the distance is L3 is 6263.

As is obvious from FIG. 4, a change in the distance between the detector 2 and the object 4 is accompanied with a change in the scattering angle of the scattered light that reaches the detector 3.

For the solution of such a problem it is essential to maintain the light source 1, object 4, and detectors 2 and 3 in a prefixed relative position.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a surface roughness analyzer which projects a beam of light from a source to an object and detects the mirror reflected light and scattered light from the object and is capable of measuring the surface roughness of the object without being influenced by any light other than that from the source, such as natural light or room illumination light, which might fall on the object. To be more concrete, the invention is aimed at providing a surface roughness analyzer capable of performing the measurement regardless of any incoming light other than that of the light source, without the need of specially shielding the measurement system.

Another object of the invention is to provide a surface roughness analyzer for detecting both mirror reflected light and scattered light from the object surface, designed so that the relative position of the object, light source, and mirror reflection detector can be easily adjusted to permit the mirror reflection detector to perform accurate detection of the mirror reflected light.

Yet another object of the invention is to provide a surface roughness analyzer of the above character capable of detecting the mirror reflected light and scattered light from the object surface having streaks of surface irregularities, irrespective of the direction of the streaky irregularities.

A further object of the invention is to provide a surface roughness analyzer of the above character capable of detecting the scattered light at a constant scattering angle as well as the mirror reflected light, notwithstanding any change in the distance between the object and the scattered light detector.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a conventional arrangement for measurement; FIG. 2 is a view explanatory of the distribution of reflected scattered light; FIG. 3 is a schematic view illustrating the relationship between the position of the detector 3 and the pattern of scattered light;FIG. 4 illustrates the conditions of the detectors 2, 3 and the object at different distances from each other; FIG. 5 is a schematic view of the first embodiment of the invention; FIG. 6 is a schematic view of the second embodiment of the invention; FIG. 7 is a schematic view of the signal processor 6A in FIG. 6; FIG. 8 illustrates the functions of the fourquadrant sensor 15 and display units 17A to 17D; FIG. 9 is a schematic view of the third embodiment of the invention; FIG. 10 is a schematic view showing the conditions of light rays in the third embodiment; FIG. 11 is a schematic view of the fourth embodiment of the invention; and FIG. 12 is a schematic view of the fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION The embodiments of the present invention will be described in detail below with reference to the drawings. In practice the surface roughness analyzer of the invention comprises at least one embodiment or all of the embodiments to be now illustrated.

The first embodiment of the invention is schematically represented in FIG. 5. Here the numeral 5 designates a modulator, and 6 and 7 a pair of filters. The modulator 5 modulates the light source 1 with a modulating frequency.

The light from the light source 1 modulated by the modulator 5 becomes chopped light with changes in intensity at regular intervals and falls on the object 4. The light thrown back is detected by the detector 2 for mirror reflected light and the detector 3 for scattered light.

Where there is an incoming light other than from the light source 1, for example from an alternating current source (commercial power supply at 50 or 60 Hz), the modulating frequency of the modulator 5 is not an integral multiple of the AC supply frequency, for example 270 Hz. This eliminates the unfavorable influence of the AC power source.

The filter 6 is connected to the output of the detector 2 to take out only the component at the modulating frequency from the mirror reflected light detected by the detector 2.

The filter 7 is connected to the output of the detector 3 to take out only the component at the modulating frequency from the scattered light detected by the detector 3.

Consequently, the outputs from the filters 6 and 7 are not affected by the influence of incoming light other than the light from the source 1, and the surface roughness of the object 4 can be accurately measured.

In this embodiment, as described above, the light source 1 is modulated with the modulating frequency of the modulator 5, and modulating frequency is taken out by the filters 6 and 7 from the outputs of the detectors 2 and 3, respectively. Hence the surface roughness of the object 4 can be measured in disregard of the influence of any external light other than from the light source 1 which might fall on the object 4.

The second embodiment will now be explained with reference to FIGS. 6 and 7.

In FIG. 6, the numeral 15 designates a fourquadrant sensor, 1 6A to 1 6C are signal processors, 1 7A to 1 7D are display units, and the remaining parts like those shown in FIG. 1 are given like numbers.

The four-quadrant sensor 15, as shown in FIG. 6, comprises four areas 15A to 15D, each of which constituting a photodetector.

To the signal processors 16A and 16B are input the outputs from the opposing areas of the four-quadrant sensor 15. Referring to FIG.

6, the outputs from the opposing areas 15A and 15C are input to the signal processor 16A, and the outputs from the opposing areas 15B and 15D to the signal processor 16B.

With the construction to be described later, the signal processor 15A is connected at the output to the display units 1 7A and 17C, and the signal processor 16B to the display units 17B and 17D.

If the display units 1 7A to 1 7D are formed of arrow-shaped lamps and arranged in a radial pattern corresponding to the arrangement of the areas 15A to 15D of the four-quadrant sensor 15 as shown in FIG. 6, the outputs from the areas 15A to 15D can be seen from the display of the display units 17A to 17D.

The signal processor 16C adds up the detection outputs from the areas 15A to 15D of the four-quadrant sensor 15. In this sense, the combination of the four-quadrant sensor 1 5 and signal processor 1 6C in FIG. 6 is a counterpart of the detector 2 in FIG. 1.

The construction of the signal processor 1 6A according to this embodiment is illustrated in FIG. 7.

The signal processor 1 6B in FIG. 6 is built in the same fashion as shown in FIG. 7.

In FIG. 7, the numeral 61 indicates a divider, 62 and 63 indicate comparators, and 64 and 65 reference potentials.

The divider 61 receives the output P from the area 15A and the output Q from the area 15C, divides the output P by the output Q, and sends out an output R, in proportion to the quotient, to the ensuing stage.

The comparator 62 gets the output R from the divider 61 and the output S from the reference potential 64, and the comparator 63 gets the output R from the divider 61 and the output T from the reference potential 65.

In FIG. 7 the components are arranged so that the output S > output T and, on the side of the comparator 62, the display unit 17A is turned on when the output R > output S and turned off when the output R < output S.

Likewise, on the side of the comparator 63, the display unit 1 7C is turned on when the output R < output T and vice versa.

Thus, when the output S > output R > output T the display units 17A and 17C are both off, when the output S ( output R the display unit 17A is on, and when the output R < output T the display unit 17C is on.

Next, the functions of the four-quadrant sensor 15 and the display units 17A to 17D will be described in conjunction with FIG. 8.

In FIG. 8 the broken lines represent equal intensity lines of reflected scattered light, the center broken-line circle H being of the maximum intensity. This means that the brokenline circle H corresponds to mirror reflected light.

(A) in FIG. 8 shows the broken-line circle H located in the areas 15D and 15C combined, and FIG. 8 (B) shows the display units 17A to 17D at work correspondingly to the conditions in (A).

FIG. 8 (C) shows the broken-line circle H brought into the center of the four-quadrant sensor 15 by modifying the relative position of the object 4, light source 1, and four-quadrant sensor 15 of FIG. 6.

The operator has only to adjust the relative position while watching the on-off conditions of the display units 17A to 17D in FIG. 8 (B) so that the lamps of those display units are all turned off. The mirror reflected light then comes into the center of the four-quadrant sensor 15.

This embodiment permits efficient positioning of the surface roughness analyzer through simple setting of the mirror reflected light relative to the four-quadrant sensor by means of the four-quadrant sensor, signal processors, and display units.

Referring now to FIGS. 9 and 10, the third embodiment of the invention will be explained.

In FIG. 9, the numerals 25 and 26 designate half mirrors, 27 designates a shade, 28 a slit, 29, a condenser, and 10 an axis. Other parts like those shown in FIG. 1 are like numbered.

The axis 10 represents the direction in which the mirror reflected light proceeds.

In FIG. 9 the half mirrors 25 and 26 are disposed in the relationship as follows.

The half mirror 25 reflects the beam of light from the light source 1, directs the reflected light to the object 4 along the axis 10, and then allows the mirror reflected light from the object 4 to pass along the same axis 10 in the direction exactly opposite to the direction of the incident light.

The half mirror 26 reflects the mirror reflected light from the object 4 into the detector 2, while allowing the reflected scattered light from the same object to pass through the mirror toward the shade 27.

The shade 27 is disposed normal to the direction of the reflected scattered light. It is formed with a circular slit around the axis 10, so that only the scattered rays of light that have passed through the slit can reach the condenser 29. The condenser 29 concentrates the scattered light that has passed the slit 28 upon the light-receiving surface of the detector 3.

As can be seen from FIG. 9, the passage of the same, constant group of scattered rays through the slit 28 is ensured regardless of whether the object 4 has streaks of surface irregularities or whether the optical system in entirety rotates on the axis 10 or not. Hence the quantity of light the detector receives re mains unchanged.

With this embodiment an object having streaks of surface irregularities can be measured through the detection of the mirror reflected light and scattered light irrespective of the direction of the surface irregularities, because the half mirror 25 and the shade 27 having the circular slit 28 coact to detect the scattered light.

A modification (the fourth embodiment) of the embodiment shown in FIGS. 9 and 10 will now be explained in connection with FIG. 11.

In FIG. 11, the numeral 35 indicates a half mirror, 86 a detector, and 37 an axis. The remaining parts are identical with those shown in FIG. 1. The axis 37 is in agreement with the direction in which the mirror reflected light advances.

In the same figure, the half mirror 35 is disposed in the following manner.

The light from the source 1 is reflected by the half mirror 35, the reflected light is directed along the axis to the object 4, and the mirror reflected light and scattered light from the object 4 are transmitted through the mirror toward the detector 36.

The detector 2 detects the mirror reflected light thrown back along the axis 37.

The detector 36 comprises an annularly shaped light-receiving surface and is disposed around and normal to the axis 37. Thus, the detector 36 detects the rays of light reflected from the object 4 and scattered around the axis 37.

The rays of light other than the scattered light being captured by the detector 36 leave this instrument undetected.

As is obvious from FIG. 11, the detector receives always a constant groups of scattered light rays regardless of whether the object 4 has streaks of surface irregularities or the optical system rotates on the axis 37.

Therefore, the quantity of light the detector 36 receives remains constant.

In this embodiment the half mirror 35 and the detector 36 provided with the annular light-receiving surface cooperate to detect the scattered light. With an object having streaks of surface irregularities, therefore, the mirror reflected light and scattered light can be measured irrespective of the direction of the irregularities.

The fifth embodiment of the invention will now be explained in conjunction with FIG. 12.

In FIG. 12, the numeral 45 indicates a half mirror, 46 a lens, and 47 an axis. The other parts are like or similar to those shown in FIG.

1.

The axis represents the direction in which the mirror reflected light passes.

In FIG. 12, the half mirror 35 is located in the manner to be described below.

The light from the source 1 is reflected by the half mirror 45, the reflected light is led along the axis 47 to the object 4, and the mirror reflected light from the object 4 is allowed to pass through the mirror along the axis 47, in the direction exactly reverse to the direction of the incident light upon the object while the scattered light from the object is also passed through the mirror.

The lens 46 is designed, with its center aligned with the axis 47 and the detector 3 located on the rear focal plane of the lens 46, to permit the detector 3 to detect the scattered light incident at a certain angle upon the lens 46.

It will be appreciated from FIG. 12 that, even if the distance between the object 4 and the half mirror 45 changes from L1 1 to L12 and thence to L13 and so forth, the lens 46 allows the detector 3 to detect always the rays at the unchanged scattering angle 611.

Since this embodiment incorporates the half mirror 45 and the lens 46 that concentrates the scattered rays of light at a given scattering angle, the mirror reflected light and the scattered light at the given angle can be infallibly measured irrespective of some changes which might occur in the distance between the detector 3 and the object 4.

Claims

1. A reflected light type surface roughness analyzer comprising a light source for directing a beam of light to an object whose surface roughness is to be measured, separate detectors for detecting mirror reflected light and scattered light from the object, a modulator for modulating the light source with a modulating frequency, end filters for taking out the modulating frequency respectively from the outputs of the detectors.

2. A surface roughness analyzer according to claim 1, wherein the modulating frequency of the modulator is different from the base frequency and its harmonics of incoming external light from AC lighting fixture.

3. A reflected light type surface roughness analyzer comprising a light source for directing a beam of light to an object whose surface roughness is to be measured, means for detecting mirror reflected light and scattered light from the object, a four-quadrant sensor for receiving the mirror reflected light, and signal processors which receive and compare the area outputs of each opposing pair of areas of said four-quadrant sensor and give outputs when the level difference exceeds a predetermined value, whereby the relative position of the object, light source, and four-quadrant sensor can be adjusted by the outputs from said signal processors to enable the four-quadrant sensor to receive the mirror reflected light.

4. A surface roughness analyzer according to claim 3, wherein the output from each said signal processor is adapted to turn on either of pairs of four opposing display units of said four-quadrant sensor.

5. A surface roughness analyzer according to claim 3 or 4, wherein each said processor for comparing the outputs from opposing areas comprises s divider for finding the ratio of the area outputs, a comparator for giving an output when the output is below a first reference level, and a comparator for giving an output when the output is above a second reference level.

6. A surface roughness analyzer according to claim 3, wherein the signal of mirror reflected light detection is the sum of the outputs from all the areas of said four-quadrant sensor.

7. A reflected light type surface roughness analyzer comprising a light source for directing a beam of light to an object whose surface roughness is to be measured, means for detecting mirror reflected light from the object, a half mirror so disposed as to reflect the light from said source, direct the same as incident light upon said object so that the incident light and the mirror reflected light are aligned exactly in opposite directions, and allow both the mirror reflected light and scattered light to pass through said mirror, a shade disposed at right angles to the direction in which the mirror reflected light passes and having a circular slit formed around the direction of advance of the mirror reflected light in the center, and a detector for detecting the scattered light that has passed the slot.

8. A surface roughness analyzer according to claim 7, wherein a second half mirror is interposed between said half mirror and said shade to reflect the mirror reflected light for incidence upon a mirror reflected light detector while allowing the scattered light to pass through said shade.

9. A surface roughness analyzer according to claim 7 or 8, wherein a condenser is interposed between said shade and said scattered light detector.

10. A reflected light type surface roughness analyzer comprising a light source for directing a beam of light to an object whose surface roughness is to be measured, means for detecting mirror reflected light from the object, a half mirror so disposed as to reflect the light from said source, direct the same as incident light upon said object so that the incident light and the mirror reflected light are aligned exactly in opposite directions, and allow both the mirror reflected light and scattered light to pass through said mirror, an annular light-receiving surface centered round the direction in which the mirror reflected light passes, and a detector for detecting the scattered light that has passed the half mirror.

11. A surface roughness analyzer according to claim 10, wherein the mirror reflected light is detected by a mirror reflected light detector disposed above the central axis of said analyzer.

12. A reflected light type surface roughness analyzer comprising a light source for directing a beam of light to an object whose surface roughness is to be measured, separate detectors for detecting mirror reflected light and scattered light from the object, a half mirror so disposed as to reflect the light from said source, direct the same as incident light upon said object so that the incident light and the mirror reflected light are aligned exactly in opposite directions, and allow both the mirror reflected light and scattered light to pass through said mirror and a lens disposed in agreement with the direction in which the mirror reflected light passes so that the respective detector can detect the scattered light at a constant scattering angle from the object, irrespective of changes in the distance between said detector and said object.

13. A surface roughness analyzer according to claim 12, wherein the lens is interposed between ssid half mirror and said scattered light detector, in such a manner that said scattered light detector is located at the focal point of the light incident upon said lens at the constant scattering angle.

14. A surface roughness analyzer according to claim 12 or 13 wherein said mirror reflected light detector is disposed above the central axis of said analyzer.

15. A reflected light type surface roughness analyzer substantially as hereinbefore described with reference to Fig. 5, Figs. 6 to 8, Figs. 9 and 10, Fig. 11 or Fig. 12 of the accompanying drawings.

16. Any novel subject matter or combination including novel subject matter herein disclosed in the foregoing Specification or Claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.