DD140589A5 - Hardness Tester - Google Patents

Abstract

The device according to the invention is applicable to the Vickers' hardness testing. It is used for estimating the output dimensions used to determine a hardness value an impression that under certain conditions in the Surface of a specimen is generated. Goal and task of Invention consist in using optoelectronic Verification means in the Vickers hardness test the measuring time too shorten and significantly increase the accuracy of measurement. On Inventively designed hardness tester comprises a photosensitive detection device, the brightness-dependent provides electrical signals and is arranged so that the Brightness is sampled in the area of an image in which the Impression or part of the impression itself in its brightness different from the rest of the picture. With a Discriminator be signals for the brightness are characteristic of the impression of signals distinguished for the brightness outside the impression are characteristic. The results of this Discriminatory steps are estimated in relation to each other Dimensions of impressions set. - Fig.3a -

Description

Hardness Tester

Field of application of the invention

That device according to the invention is applicable to the Yickers hardness test "Bs is used to estimate the dimensions of an impression used as the starting point for the determination of a hardness value, which is produced in the surface of a test specimen while maintaining certain conditions."

.Characteristic. "Of the known technical solutions

The Vickers hardness test is a known test method for Härtebestimmungo In the conventional Vickers testing procedures one Diamantpyrainide is pressed with half a point angle of 68 ° lower predetermined load to the surface of the material ^ whose hardness are tested Soll ₉ and the resulting impression is under a visual microscope equipped with movable orifices in the image plane of the objective *. The user can regulate the position of the panels by means of adjusting screws. "Beira use the screws are pressed" until the edges of the orifice plates coincide with diagonally opposite corners of the enlarged image of the impression _s with the image aligned? that a diagonal is perpendicular to the edges of the orifice * The adjusting screws for the orifice are

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connected to a mechanical counting device which indicates the opening width of the metering orifice edges. Under these circumstances, the aperture width of the metering orifice edges is a measure of the length of the diagonal of the image, and this length is displayed in the mechanical metering device *

The measuring process is then repeated on the other diagonal of the image of the impression. The average of the diagonal length is calculated from the known magnification of the microscope and into the relationship

where HV is the Vickers hardness,

P the force applied by the Ein & ruokpyramide (kp)

and d is the median diagonal length (mm.) of the

Impression mean »

This method is widely used and provides useful results for a large number of materials but is time consuming and depends on the skill of the examiner in terms of accuracy _a. Errors can occur during fatigue.

Object of the invention

The aim of the invention is to optimize _s test by eliminating subjective errors during the measuring the Vickers hardness '©'

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Explanation of the ₁ article of the "invention"

The invention has for its object to shorten the measurement time in the Vickers hardness test by using optoelectronic -Naohweismittel and to increase the accuracy significantly

This object is achieved by a hardness tester for estimating the dimension of an indentation $ serving as an output for the determination of a hardness value, which is produced in the surface of a specimen to be examined for hardness according to certain conditions, provided with an imaging device which images an image plane of the surface area containing the impression

According to the invention, such a hardness tester comprises a photosensitive camera arranged in the image plane and capable of providing electrical signals indicative of the brightness levels within the image of said surface area, as well as a discriminator circuit receiving these electrical detection signals and electrical signals each the level of which is characteristic of the brightness in an image area within the image of the impression differs from signals whose level is characteristic of the brightness in an image area outside the image of the impression, whereby the said dimensions can be determined.

In the preferred embodiments of the invention, a Yielfacette impression is not illuminated in the normal direction, but the images of the impression are subdued

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generated obliquely incident light. That is, the impressions are illuminated not from the IT normal direction, but with a light incident at an angle to the normal, so that certain facets of the impression appear particularly bright.

In particular, the impression is illuminated with at least one collimated beam of light incident on corresponding facet surfaces of the impression at angles such that "the beam (s) are reflected from the associated pacet surface in the ITorraal direction." This mode of illumination leaves bright images of the facets The impression on a darker background can give rise to considerable advantages in terms of measuring accuracy,

In a Xusführungsform of the hardness tester according to the invention has the photosensitive Hachweiseinrichtung a single light-sensitive element on _e Furthermore, a scanning device is provided that performs an Abtastrelativbewegung 'between said individual light-sensitive element and the image of the surface area in which the impression is attached, _f when the Device used for estimation of dimensions of impression «.

Another embodiment of the apparatus employs a photosensitive detector having a one-dimensional array of photosensitive elements. The scanner is designed to provide a scanning movement perpendicular to the rectilinear array of photosensitive elements between the device and the image of the photosensitive body during the measuring process Surface cooking Si in which the impression is applied ₉

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causes.

Me photosensitive detection device of a hardness tester s according to the invention may be also permitted in such a manner that _p a two dimensional array of photosensitive elements is given.

In a device whose detection device has a single photosensitive element _s , the scanning device can be designed differently. An embodiment of the scanning device has a tongue with said photosensitive element at its one end _s also a tongue holder to which the other end of the tongue is attached »This tongue holder is linearly movable _? j such that the photosensitive element in which the impression iet placed over the image of the _{OberflächenbereichSf?} The scanner also has a device which causes one end of the tongue with the photosensitive element to oscillate transversely to the direction of movement of the tongue holder. "

Another embodiment of a single light-sensitive element detection device of the present invention comprises a movable support on which the element is mounted. The support is linearly movable such that the photosensitive element overlies the image of the surface area. in which the jolt are attached * is guided "An opto-mechanical Torrichtung allows said image on the photosensitive element transverse to the direction of movement of said support oscillate. · ¹

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The opto-mechanical device can be realized by a mirror which can be made to oscillate and in this way moves the image of the impression back and forth.

With a hardness tester, the light-sensitive evidence "means a one-dimensional array of light sensitive elements ^ has, the scanning device is a vertically movable to the rectilinear arrangement of the elements support for this arrangement as well as a sampling of" This sampling leads the Naehweissignale of the Respective photosensitive members _from? wherein the elements for generating the Naehweissignale are scanned sequentially in cyclic repeated order?

With a hardness tester? the light-sensitive detection means has a two-dimensional array of light sensitive elements ₉ is a sampling circuit is provided which derives the ITachweiesignale from the respective photosensitive elements _S wherein the elements of each row of the array in sequence one after another and the rows of the array in turn sequentially in cyclic repeated sequence scanned? / er & en «

According to the invention, the discriminator circuit of a hardness tester of the type proposed receives a comparator aufg the lachweissignale and compares them with a comparator supplied threshold signal compares ₉ According to the results of the comparison comparison signals are given, which have either a first Pe gelhöhe * which is indicative of a Ütachweissignalj that characterizes the brightness in a picture area within the image of the sinj, or, a second level that is indicative of a detection signal? that the brightness in

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one characterizes an image area outside the image of the impression. In addition, a sample and hold circuit is provided which receives said comparison signals and responds to the first level comparison signals so as to output a sample output of predetermined magnitude after the disappearance of the first level comparison signal during one of the arrangement used of the photosensitive elements dependent period of time

This time interval is equal to a whole scanning period of the array in a one-dimensional array of photosensitive elements, and equal to the time required for the photosensitive elements in a single light-sensitive element arrangement equal to half a period of the relative vibration between the image and the element j Scanning a line of order _θ

In a further embodiment of the device, a gate circuit connected to the sample and hold circuit is provided, which receives the sample output signal and produces measurement signals on "ni-rant generated in the device". These measuring signals are characteristic of movements of the support of the scanning device, be it a system with a photosensitive element or with a one-dimensional arrangement of a plurality of photosensitive elements ₉ further characterizing the respective successive scans of the last-mentioned arrangement or for the scanning of respectively successive lines in one System with Two-Dimensional Arrangement of Photosensitive Elements «The gate circuit only passes the measuring signals mentioned above into a measuring circuit

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of the device if the scan output signal has the selected value.

The discriminator circuit has a further gate circuit which receives the detection signals and the comparison signals. It forwards the% chweiss signals when the comparison signals have the second level level. An averaging circuit is provided, and the IT detection signals relayed by said another gate circuit further receives a summing circuit which generates a reference level signal generated in the discriminating circuit. and receiving a common average signal from the averaging circuit and passing the sum of the reference level signal and the averaged signal as a threshold signal to the comparator *

In a hardness test devices whose Verify Einriehtung a one-dimensional or two-dimensional © arrangement of several photosensitive elements has ^, the discriminator circuit is formed accordingly, "Such a circuit includes a comparator which receives the Nach- v / eissignale and this with a comparator supplied threshold signal compares _o According to the results of the comparisons are comparison signals abgegebeiig have either a first level height which is indicative of a detection signal which characterizes the brightness in an image area within the image of the impression _s or a second level height which is indicative of a detection signal which the Brightness in an image area outside the image of the impression is characterized. In addition, there is provided a scanning and holding circuit which receives the said comparison signals and the comparison signals of the first level

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reacts in such a way that a Abtastausgangssignal certain height is delivered. This sample output is maintained for a period of time equal to the time between sampling a single element of the array and the next.

Connected to the sample and hold circuit is a gate circuit which receives said sample output and further address signals which are generated in the sample circuit to scan the respective elements of the array. A single element will then provide a detection signal whenever the device is placed An address signal is supplied. The address signals are only supplied to a measuring circuit (counter) of the device if the sampling output signal has the selected value

For a better understanding of the invention and to. ihare practical application, will be described below with reference to the drawing several embodiments described The figures show?

Pig * read the schematic representation of an embodiment of the Hüfigkeitgergerät test according to the invention

Pig, Ib: a wavefront diagram,

Fig. Ic: a modified. Embodiment of the hardness test · =, device according to Pig "1a in a schematic representation,

2 is a block diagram,

Fig. 3as a further embodiment of the invention (schematically),

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3b s a waveform ~ diagram,

4as a block picture,

Fig. 4b. a diagram,

Fig. 5a, 5b ,, 5ci possibilities for lighting

a surface to be examined according to an embodiment of the invention (schematically) _f

Fig. 6ai a further embodiment of Er

invention (schematic) _s

Fi _e 6BS a \ Vellenform ~ _s chart

Fig _e ^: 7 s is a schematic representation with number

rich details in a partially sectioned side view of an embodiment of the invention ^

Fig. 8a _s 8b, Oc s possibilities for lighting

a surface to be examined according to an embodiment of the invention (schematically) s

FIG. 9 s parts of a further embodiment of the

Invention (schematic) ©

In the embodiments of the invention, optoelectronic means are used in the context of the photosensitive laughter device whose electrical characteristics depend on the prevailing illuminance on them. Such devices are known per se and have been used in a variety of applications, when their be. illumination-dependent parameters in conjunction with suitable electronic circuits can be used to generate electrical output variables for measurement and control purposes.

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For example, the electrical conductance of a silicon photodiode increases as the incident light energy increases, and when a battery or other DC voltage is applied to the silicon photodiode, the current flowing in the photodiode depends on the light energy incident on the photodiode. This current change can be amplified electronically and displayed on a suitable measuring device, so that light intensities can be measured down to very low values.

Photodiodes suitable for the measurement of low brightness levels can be used in the hardness tester according to the invention, in which at least one such photodiode used in the photosensitive detector is arranged with its photosensitive surface in the image plane of a microscope objective. The microscope is a part of the imaging apparatus of device. The image of the impression in the surface of a specimen to be examined for its hardness normally appears enlarged. The photodiode (s) used in such an embodiment of the invention has a size _. which are small compared to the expected size of the magnified images of impressions to be examined are * The output of an electronic amplifier circuit for the photodiode of the photosensitive Uaevviieißsinrichtung in a. Embodiment of the invention depends on the location of the photodiode with respect to the image of a under examination illuminated impression from "When the Abbildungsniittel of the device, are configured _f that an impression in the -Formalenrichtung beleuchtet..wird through the microscope objective through appears the image of the Impression as a dark square opposite a lighter one

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Background, and the output of the amplifier circuit has a low value when the photodiode is within the image of the impression - and a high value when it is outside this image ^

In an embodiment of the invention shown schematically in Fig. 1a, a photosensitive laughter device comprising a single photodiode 1 is used. Scanning means are used which sense relative movement of the photodiode 1 relative to the image in an image plane of the device Inducing microscopes »The photodiode 1 is mechanically excited , oscillations in the image plane of the microscope (not shown) to observe an impression generated in the surface to be examined * For this purpose, in the scanning device, for example, a vibrating tongue 2 is used, which by schematically indicated mechanical or electromagnetic means 2a _s is caused to vibrate, for example by plucking _s "The amplitude of vibration is chosen so large that it covers the largest zn expected image ^ The imaging devices of the device provide the illumination of the impression and the generation of a B. In the present case, the imaging device is a microscope (not shown) ", - The tongue 2. is attached to a displaceable tongue holder 3 the tongue 2 and thus the photodiode 1 vibrates-the tongue holder 3 in the direction of the arrow (transversely to the direction of oscillatory movement of the photodiode 1) moves «wosu example, a spindle 5 is used» which is driven by a (not shown) motor ©

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The oscillation frequency of the tongue 2 and the feed rate of the tongue holder 3 are coordinated with one another such that the distance traveled in the direction of the arrow 4 during a period of oscillation of the tongue 2. The photodiode 1 thus scans an image 6 of an image of an impression, designed in the image plane 6a, on an orbit, which is indicated by the dotted line 7. The output of an amplifier circuit (not shown) electrically connected to the photodiode 1 provides electrical information signals which, depending on the position of the photodiode 1, vary with respect to the image 6 of the impression. During a typical half cycle period 8, the electrical detection signals generally change in accordance with the profile shown in Fig. 1b. It can be seen that the electrical detection signals vary between level values indicating? that the photo diode 1 is within the image 6 of the indentation or outside the image 6 of the indentation. In the case of oscillatory movements of the photodiode 1, the image of the indentation does not of course overlap, no change in the level of the detection signal occurs, of course This difference forms the starting point of the Hachweist technique used in this embodiment of the invention. "The difference can be used to influence a suitable measuring device * connected to the displacement mechanism of the device * ^;

The block diagram Pig * 2 is an example of the possibility of exploiting the changes of the electrical single-white signals. The output quantity of an electrical information signal in a photodiode amplifier.

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Circuit 9 is fed to a discriminator circuit having a comparator 10 in which it is compared with a predetermined fixed threshold electrical signal coming from a reference circuit 11. This fixed threshold electrical signal is approximately midway between the upper and lower levels - (See Pig, -1b) of the electrical output of the photodiode amplifier circuit 9 »and the output of the! Comparator 10 provides discriminator signals which are positive or negative electrical signals, depending on whether the photodiode 1 (Fig. 1a) inside or outside the image of the indentation (Pig "1a) β For estimating the dimensions of the indentation, the discriminator signals into one. Out correlation device 12 includes a sample and hold circuit, the only positive Diskriminatorsignale (relatively high level) "to the comparator 10 responds and provides an electrical output which _o during a time interval _s, the (a half-oscillation of the tongue. 2 Fig 1a) corresponds} after a last positive discrimination signal from the comparator 10 is maintained "While the photodiode 1 (Figo-1a) on the image 6 of the indentation (Fig _ö 1a) of time, oscillates, the electrical output of the sample and hold circuit 12 held constant and relatively high, but when the advance in lease of the arrow 4 (Pig, la) moves the photodiode 1 just beyond the image 6 of the impression, the electrical output of the sample and hold circuit 12 disappears within one half cycle of the tongue 2 (FIG. E ¹ Xg ₀ Ia) ₀ Diesel electric output can then be used to excite a gate 13, ie e electrical measuring signals from a converter 14 to a compatible measuring circuit 15 only eh »leaves while the electrical output of the sample and hold

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The measuring circuit 15 thus measures only the signals from the transducer H> while the photodiode 1 (Pig · 1a) has the image of the indentation (FIG. 1a) in each half cycle of the oscillation of the tongue 2 (FIG · 1a) passes over ·

In the converter 14 may be a device mounted on a fixed support part 17 and connected to the spindle 5 (Pig x 1a) _s is to generate a sequence of electric pulses or measuring signals _au? which correspond directly to the rotation of this spindle relative to the fixed support member 17 "" Such, commonly referred to as analog / digital converter device can v linked via the gate 13 to the measuring circuit 15, which is here an electrical counter may be, which counts the pulses generated by the a / D converter due to the rotation of the spindle 5 becoming when the gate circuit 13 in accordance with the photodiode output in the above-described V / else operates _f pulses are counted ^ when the oscillating photodiode 1 over the magnified image 6 of the indentation in the direction indicated by the arrow 4. The number of pulses counted during one of the »like advancing movements is thus a measure of the diagonal distance IG of the indentation. The positive and negative discriminator signals are thus written in FIG Relationship to corresponding image areas inside and outside, the image 6 of the E indrucks set _? to allow an estimate of the dimensions of the impression *

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The converter 14 may also be formed as a linear variable differential transformer (LVDT), which is part of an AC circuit and is directly connected to the tongue holder 3 and the fixed support member 17. The electrical output of the AC circuit associated with the LVDT may be directly in the position of the tongue holder 3 in the direction of the arrow 4 are calibrated relative to the fixed support member 17, and the measuring circuit

15 can be formed so that _s the diagonal line

16 as the difference between the initial position signal when the photodiode 1 first detects a corner of the image 6 of the indentation ^ and the end position signal j when the photodiode 1 no longer detects the image 6 of the indentation after having traveled the full stretch of one diagonal of the image 6 has passed through the impression in the direction of arrow 4 «

The transducer 14 may be formed of a linear displacement effecting having diffraction gratings for generating moire fringes as optical _f, said opto-electronic means Sindo provided for detecting the displacement of fringes A connected with the tongue holder and the fixed support part 17 apparatus produces a sequence of electrical impulses (measuring signals), which relate directly to the displacement of the tongue holder 3 relative to the fixed support member 17 in the direction of arrow 4 «By linking the electrical output of a converter of this kind via the gate circuit with the measuring circuit 15 * to be designed as an electronic pulse counter can _? can the diagonal section 16 be specified in pulse numbers _{? s} has been described counted during movement in the direction of arrow 4 in the same manner as described above for the analog / digital converter

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become"

The above-mentioned converters are known per se and are only by way of example mentioned "One can also use other types of displacement or distance measurement, provided that these methods provide, directly or indirectly §in electrical signal suitable for transmission by the gate circuit 13 in the measuring circuit aen is. Of course, moreover, the design of the corrugator 13, such as the measuring circuit 15, can be varied to suit the shape of the electrical signal transmitted by any type of displacement transducer.

The device of Fig. 1a will be described for the sake of completeness, but it is not the preferred embodiment for this particular application * because _? as can be readily seen, a suitable means must be provided ;, with which the tongue is caused to oscillate in the proper frequency 2 'while the photodiode 1 is accurately held in the image plane, "although stand For this purpose, some methods are available _s For example, the plucking of the tongue 2 with subsequent oscillation in the natural frequency of the tongue 2 of the drive ά & Tue 2 with a selected frequency by means of mechanical or electromagnetic means, it is made, however, given the existing different types of multiple photodiode array another proposal « With these multiple arrangements, numerous photodiodes can be arranged in the image plane of the microscope along a straight line perpendicular to the diagonal to be measured. A possible modification of the device according to Fig. 1a with a single photodiode should, however, be mentioned in this modification

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a single photodiode mounted on a rigid sliding support instead of on the oscillating tongue 2, and an ôptomechanische device makes the image of the impression on the photodiode in a direction perpendicular to the arrow 4 in Fig * 1a marked "feed direction swing" Oscillating mirrors are used, provided that its movement is well defined, as is the case with mirror galvanometers commonly used in UV recorders ·

Pig ". ' 1c illustrates such an arrangement schematically as a modification of the single-photodiode device of Figure "1a represents _e Mach FIG» Ic is disposed at one end of a rigid component 202 201, whose other end is attached to a bracket 203, a single photodiode ₉ in Direction of the arrow 204 by means of a threaded spindle 205 can move v / ground, which is driven by a (not shown) motor o The spindle 205 is on a fixed support member 21? Inappropriate

The photodiode 201 moves in an image plane 200a of the device, which contains an image 200 of an impression.

The image is moved back and forth in the image plane, for example, by elements 195 to 199 (FIG. 1c)

A part of the surface of a specimen 199 ₉ into which an impression to be examined is pressed is imaged by means of a microscope objective 198 _{S of} a prism 197 and a mirror 196 in the image plane 200 a. The mirror 196 is oscillated to and fro, which requires a drive In this way, a vibrating image is created in the image plane 200a.

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An arrangement with a light-sensitive compartment Weis device consists of a multi-photodiode array is shown in Pig _e 3a, after which a linear (one-dimensional) array 18 on an arrangement supporting carriage 19 in the V / is mounted else _f that the photodiodes of the array in the plane The linear array 18 is made * such that its longitudinal extent is comparable to the dimensions of the image 20 of the largest anticipated impression, and the distance between adjacent photodiodes of the array is practically constant and comparable to the resolution. which is required for the measurement of the diagonal distance of the image 20 ·

Such an arrangement 18 may comprise, for example, 256 photodiodes arranged on a straight line at a distance of 0.025 mm. However, other types of arrangements are known which comprise up to 1024 photodiodes spaced 0.0125 mm. Such arrangements generally consist of a one-silicon chip on which a series of photodiodes have been photonucleated, and the same principle can be applied to the same Such an arrangement comprises a scanning circuit which is capable of interrogating the lighting condition of each photodiode in turn in accordance with a sequence of electronic address pulses (address signals) in a circuit separate from the array and connected thereto by conductor wires The level of illumination received by a given photodiode will result in a corresponding amount of electrical conductance at the photodiode and a loss of electrical charge from a photodiode connected and mounted on the same silicon chip

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Circuit · 'If a photodiode is driven by the stemming from the separately mounted circuit electronic pulses ₉ performs the drainage of electric charge through the illuminated photodiode to a decreasing voltage level at the photodiode and to a greater supply "of electrical charge to the voltage predetermined at a One of these parameters can be monitored to estimate the level of illumination prevailing at the particular photodiode, and the array then provides a corresponding short-duration signal output. This process sequentially progresses for all photodiodes of the array in turn, and the output quantity is thus a series of short pulses which are characteristic of the illumination level which exists at each one of the diodes of the device. The time required to scan the device in this form can be varied by taking the frequency of the pulses in the It may, for example, be 10 ms. The sampling circuit 118a for the arrangement 18 is schematically indicated in FIG. 3a

The serial signal output during a single scan of the array 18 represents a pieced analog to the continuous signal _p from the single photodiode 1. 1a, during a single half oscillation of the tongue 2, and when the output of the device 18 is amplified by the usual electronic means, the resulting electrical signals at the amplifier output have the shape indicated in FIG. 3b, These electrical information signals can be used in discriminator circuits and correlation devices in the manner already discussed in connection with FIG.

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Apart from the fact that the amplifier 9 must now be compatible with the output signal of the arrangement 18 and the sample and hold circuit 12 of the correlation arrangement now every positive signal from the comparator 10 during the duration of a scan of all photodiodes in the assembly 18th * maintained must. The gate circuit 13 can then, as already mentioned, be used ^ to transfer measuring signals from the converter 14 in the measuring circuit 15.

In the apparatus of Fig. 3a, the carriage 19 forms part of the scanner of the apparatus, and the linear displacement of the carriage 19 along the fixed guides 21 leaves the photodiode array 18 in the direction of the arrow 22 over the enlarged image 20 designed in the image plane 20a of the impression. The movement can be done by means of a threaded spindle 23 which is arranged in a fixed support 24 and cooperates with a threaded bore 25 in the carriage 19. The threaded spindle 23 can be driven by a (not shown) motor or other suitable means ^ so that the carriage 19 and the assembly 18 are set in motion in the direction of the arrow 22 at a speed determined by the required measuring resolution in detecting the opposing cokes 26, 27 of the image 20 of the impression and the speed of electronic scanning of the photodiodes in the assembly depends 18. "for example, if a measurement resolution of O _s O25 mm is required," the arrangement must be advanced 18 in the direction of arrow 22 to Oj025 mm in the period, which is necessary for a complete electronic scanning of all photodiodes in the array 18 · ^ hen this period is 10 ms, must the sled n-19

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with the arrangement 18 opposite the image 20 of the indentation in the direction of the arrow 22 by 2.5 mm / s, and the speed and the pitch of the threaded spindle 23 are to be selected accordingly. ¹ If these criteria are met, other means may be used used for the advancement of the carriage 19 and the assembly 18 v / earth »

The measurement of the feed can be made with all the means associated with the Pig. In connection with the device according to Fig. 3a, a suitable converter (not shown) could be switched on, which supplies electrical measuring signals j which correspond to the displacement or the position of the carriage in the direction of the arrow 22 with respect to the fixed support 24. Instead, a converter may be used which provides electrical measuring signals dependent on the rotation of the threaded spindle 23 relative to the fixed support 24. In operation of the apparatus, the converter H (Pig * 2) would provide electrical measurement signals which are in definite relation to At the beginning of their movement, the arrangement 18 in position 18a (shown in dotted outline) does not coincide with any portion of the image of the impression, and the serial output signal of the arrangement would be practically constant and above the reference threshold level, the ™ in the reference circuit 11 of Figure 2 is _e is "Under these circumstances, no signals from the transducer 14 in the measuring circuit 15 of FIG. 2 'reach''. During the advancing movement in the direction of the arrow 22, however, the arrangement hits the corner 26 of the image 20? and. at least one photodiode would be illuminated less brightly than the remaining ^ and the output signal or * the output signals

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As a result, these photodiodes (η) would fall below the general level and below the reference level set in the reference circuit 11 of Fig. 2. Under these circumstances, measuring signals would be taken from the converter 14 into the measuring circuit 15 of Fig. 2, and Figs Puncturing the sample and hold circuit 12 would cause these signals to continue to be asserted during the period of complete electronic scanning of the photodiodes in the array 18 after the last of the output signals was received below the general level at the comparator 10 (FIG. after the last positive or relatively high discriminator signal), at which time photodiodes in the direction of the center of the array would again emit signals below the reference level, thereby causing measurement signals from the converter 14 to continue to enter the measuring circuit 15 of FIG 2 "This process would be repeated, - since the Anordnun gselemente were sampled in a cyclic repetition and still _s absence constantly convertor signals in the measuring circuit 15 of FIG «· 2 to the arrangement 18, the image 20 in the direction of arrow 22 is completely swept hätteβ during a complete movement of the assembly 18 from the position 18a to the position 18b would thus transducer signals are recorded in the measuring circuit 15 according to the length of the diagonal · image 20 of the impression «

In a modified embodiment in which no transducer 14 is used, "pulses ₈ used to address a photodiode of the device will be used instead of the signals emanating from the transducer as a measurement. Signalo introduced into the measuring circuit 15 For example, the pulses _s for addressing the first photodiode

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& υy .Äjw _{54 569 / 1β}

of the arrangement used in corresponding scans of the arrangement.

It will be readily appreciated that the threshold voltage generated in the reference circuit 11 of Figure 2 must be between the voltages resulting from the amplification of array signals corresponding to photodiodes exposed to high and low levels of illumination in the image plane. wherein the high level representing the illumination of the surrounding the impression surface of the Härteprüfkörpers, and the low level assigned to the impression itself shall find in principle, it would be desirable _s Besugsspannung generated in the reference circuit 11 according to Pig ₀ 2 as close as possible to the higher voltage adjust " which corresponds to the illumination of the surface of the hardness specimen surrounding the indentation so as to supply measuring signals from the transducer 14 to the measuring circuit 15 as quickly as possible after any photodiode in the arrangement of Pig * 3 has received a lower illumination level after entering the image of the indentation " To this On the contrary, the sensitivity of detection in the image would be increased, whereby the accuracy of the measurement of the diagonal distance would be improved. However, difficulties would arise if the reference circuit 11 of Fig. 2 were used in this way, because the higher voltage, which results from the illumination of the impression surrounding the specimen surface, not fixed, but in an undefined manner from specimen to specimen changes «. If the reference voltage was fixed, the sensitivity of the image detection would then change from one test piece to the other, and the measuring accuracy would therefore change.

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A measuring technique in which this difficulty could be eliminated, works with a circuit of FIG. 4a. The incoming signal from the photodiode array is amplified in the input amplifier circuit 9, and the resulting electrical detection signals are fed to the discriminator circuit consisting of a comparator circuit 10 and a parallel gate. This gate circuit 28 is turned on in the absence of a positive discriminator signal from the output of Comparator circuit 10 and then causes electrical detection signals from the amplifier circuit 9 to enter into a mean value circuit 29 (averager). The average voltage "· value output from the circuit 29 is fed to a summing amplifier, where it is added to the reference voltage from the reference circuit 11 _s and the sum of these two voltages is the Komparatorschältung 10 is supplied as threshold voltage. The comparator circuit 10 thus receives a uniform electrical signal corresponding to the average photodiode output resulting from the general illumination of the surface of the particular specimen being tested and the reference voltage from the reference circuit 11, the latter voltage being within narrow limits and opposite the output of the averaged circle 29 This is shown in diagram Pig. 4b, in which voltage levels 31 ₉ 32 ₉ 33 ₉ which correspond to the output values of mean value circuit 29 or reference circuit 11 and summing amplifier 30 are represented as lines , whereas successive signals from photodiodes in the arrangement * amplified by the input amplifier 9s exceed the voltage level 33, a negative output at the comparator 10 ₉ and the gate circuit 28 cause input signals to enter into the averaging circuit 29;

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is maintained by a current value of the signal 31, which corresponds to the general lighting of the specimen surface. When any photodiode in the array is exposed to a lower illumination level, the output of the amplifier 9 falls below the voltage level 33 and a positive output is produced in the comparator 10. By this output, the gate is caused to enter photodiode signals This signal will be kept practically constant in the absence of input signals for the averaging circuit 29. The positive output signal of the comparator 10 also energizes the sample and hold circuit 12 and from there from the gate circuit 13 _S so that signals from the converter 14 enter the measuring circuit 15, as described above

While the foregoing description speaks of positive and negative voltage levels for particular signals, the polarities can be changed to accommodate certain electronic circuit requirements, provided that the mode of operation does not change thereby will ^": for example, can beiden.Eingänge to the summing amplifier 30 via an inverted and a non" inverting terminal be done '' In this case, the signals from the averaging circuit 29 and the Bezugsstrorakreis 11 may have the same polarity and do not need as before described, opposite polarity'aufaufweisend

Another essential aspect of the use of the described arrangements for measuring the diagonal distance

, 209 25 3 -27- 12.3.1979

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a pyramid-like impression is the rejection of all surface features that do not represent the impression in question · This need not always be possible with the systems described so far _s because 'these systems are designed so that contrasts detected in the enlarged image of the specimen surface becoming and in illuminating method _f which is normally used for measurements of Vickers hardness can traces grinding "and give rise in the image porosities or other surface phenomena contrast areas that are comparable to those resulting from the impact of the test pyramid itself"

In procedures that should solve this difficulty? it tries to get _$ properties of the impression that other Oberflachermierkmalen, - that may occur in the visual field of the microscope, are not pronounced · The obvious feature of the hardness impression is its geometric Fora that of the impressions of a pyramid with a square base and a half apex angle is of 68 ° size caused in the test specimen, and it is possible, the discriminator, the correlation means and the measuring circuits, such as those described above _s .auszuführen so that measurements are rejected which do not correspond to the expected geometric pattern * For example, in the arrangement according to PIg ₆ '3a, the frequency of the diode scan in the array 18 and the feed rate in lease of the arrow 22 are chosen so that at each scan of the array IS a ganK - number, for example, two more photodloden more in the Location are that Figure 20 of the Do jerk prove than any% ^r orhergehenden Abtastungc iTach passing through the center line 34.des image 20 the situation is umgekehrtj

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and zv / ei photodiodes less are able to detect the image than in any previous scan. This behavior can be achieved by turning on an up / down counter (not shown) which, in the presence of a positive signal from comparator 10, would count the photodiode address pulses supplied by the separate circuit (not shown) which powers the array. A limit circuit (not shown) would pick up signals from the forward / reverse switch that correspond to the number of photodiodes that detect the impression on each scan of the on-order, and this circuit would be designed to operate If the absolute value of the change in the number of photodiodes counted on successive electronic scans of the array differs markedly from the expected rate of increase, for example, the expected rate of increase 2 would be Begrenzungsschaltung so executed.verde n ₉ that they are the measuring circuit 15 would lock and reset "outside the range of 1 to 10", thus allowing for smaller deviations from ideal image geometry, dubious measurements that would be due to the presence of other surface features in the field of view but would be eliminated ",

This method is technically feasible, but could have the disadvantageous consequence? that no measurements are made on specimens that show a noticeable number of surface defects besides the. DiamantpyramideneindruGk have, because the measurement is prevented _s if the arrangement at any point during its Vorschubs über.d. The image

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of the impression on the image of another surface merkmais pushes. This can be countered by providing an additional digital electronic circuit which further analyzes the signals emanating from the photodiode array, thereby discriminating in favor of the indentation geometry, but can add considerably more difficulty. occur in the electronic signal-processing circuit, if further criteria for the adoption of the diagonal nines solution be incorporated ^

A simpler approach is used in an instant preferred embodiment of the invention. An imaging device is provided which provides a different illumination method from the illumination described above in order to make certain facets of the impression appear particularly bright while achieving improved contrast in the image while simultaneously reducing the contrast of all other surface features in the image wirdο reduced images Sin to used method relies on the fact _s that impressions that with the polyhedral are jerk bodies of the specified form (ζ · ^Β: pyramidal diamond indenter) can be produced in a homogeneous deformable material replicate _s the geometry of the indenter very accurately and four possess essential planar facets _? how well mirrored light reflectors work ". In addition, in the Yickers Cure Test, the half-angle (68 °) of a sensation produced by the square-faced indentation pyramid is sufficiently large to make a parallel bundle of light incident on any given facet at an appropriate angle from the entire surface of that facet toward the normal Reflecting on the IT surface of the hardness test specimen

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This process is described in Pig. 5a, in which an indentation 35 is drawn in the rectangular section of a test specimen 36 ', whereby one of the facets 37 of the impressed impression 35 is struck by a parallel ray bundle 33, 38a. Since the facet 37 reflects approximately specularly, the greater part of the specimen becomes reflected light as a parallel beam 39 * 39a under a Y / inkel 40 relative to the normal 41 on the facet 37 forward, wherein the angle 40 is equal to the angle of incidence 42 of the StrahlenbUndeIs 38, 38a « ^; In addition, since the half-angle 43 of the indentation 35 is greater than twice the complementary angle (ie * greater than 60), the angle 44 of the incident beam 38 38a relative to the normal 45 on the surface 46 of the specimen 36 can be chosen to be that Radiation bundle 39 »39a runs along the hormones 45. At a half-angle 43 of 68 °, the angle 44 of the incident beam 38, 38a is 44 ° as compared to the normal 45. It can be seen that a microscope (not shown) forming part of the imaging device of the hardness tester or another for viewing the Impression-capable optical device whose optical axis is substantially in the direction of the normal 45 gives an image of the illumination illuminated in the manner indicated, in which one facet will appear much brighter than the other facets and the remaining parts of the specimen surface Processing marks or porous spots, can only deliver bright images? if they have considerable area shares? ge.genu.ber whose orientation to the incident light beam 38 =, 38a quite similar to that of the brightly illuminated facet 37 is _e dem.seltenen In the case of a very similar orientation, it is unlikely that the

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Reflecting properties of such a range as those of the facet 37 are equal, and the brightness of the image of such an area would be low as compared with that of the facet 37 of the indentation 35. This has been confirmed in numerous experiments, and it has been found that this illumination method, when viewed in the direction of the line of specular reflection from a facet in the image of this facet, produces a particularly high brightness, thus providing a possibility for this facet to differentiate from other surface features «

The picture of the impression 35 with illumination according to FIG. 5a and designed by a microscope or other suitable optical system constituting a component of the device * whose optical axis is substantially parallel to the hormone 45 has the appearance of the illustration in FIG. 5b, with the illuminated facet 37 as a bright triangle 47 and the other three facets appear as relatively dark triangles 48, 49 * 50. "The image 51 of the surface 46 surrounding the impression 35 in the image plane 51a is generally somewhat brighter than the images of the non-illuminated facets of the impression because of the diffuse reflection. but the image brightness in this area is significantly below that in which heal triangle 47 *

If the method shown in Fig. 5a is used to illuminate two adjacent facets, then this has to be done by a microscope or other suitable optical system whose optical axis is parallel

- "λ

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runs to the normal 45, designed image looks like Pig. 5c, wherein the two illuminated facets appear as a uniform bright triangle 52 and the two non-illuminated facets as a relatively dark triangle 53. Designed in the image plane 54a image 54 surrounding the impression surface of the specimen is lighter than if only one facet would be illuminated, but remains significantly darker than the triangle 52 * Of course, this type of lighting, in which an image of FIG _e 5c arises , particularly suitable for the diagonal measurement in the Yickers hardness test, because a line from the corner 55 to the corner 55a of the impression at the boundary between the bright triangle 52 and the dark triangle 53 represents just the diagonal of the impression «Thanks to the brightness of the triangle 52 This diagonal can be detected particularly easily by opto-electronic means, while retaining the advantages peculiar to this method of illumination with regard to the differentiation of other surface features. "

The application also to other aspects appear in conjunction with Figs. 5a through 5c described illumination method in the embodiments of the invention, particularly favorable The individual photodiodes of the array 18, for example of FIG _e 3 & _s also have small size so that the required resolution of an in the image plane, in which the arrangement 13 is provided, is guaranteed image of a Sindrucks guaranteed. The small size of the photodiodes may cause their sensitivity to changes in the brightness level to be relatively low. If that is the case, it may be necessary to ensure that they are examined by the

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In this way, a sufficiently bright image is produced so that the determinations of the dimensions of an impression can be made sufficiently fast. Such a sufficiently bright image is produced by the illumination method described in connection with FIGS. 5a to 5c the use of reflective reflection on facets of the impression * easy to achieve · '

Pig are _e 6a is a showing in Pig - that is illuminated as described with FIG _e 5c "3a comparable device for examining an image 56 of an impression again""The amplified output signals 57 (electric detection signals) during a single electronic scanning of the photodiode array 18 appear in the image plane 56a of the image 56 as the representation in Figure 6b, from which the strong response of those photodiodes of the arrangement can be seen, which coincide with the image of the brightly lit facets of Sindrucks. This device can be used in the manner already described in connection with the electronic circuits of Pig * 4a which are used to detect device signals corresponding to greater brightness and not lower brightness * The comparator 10 of the discriminator circuit therefore gives a positive signal to initiate the measurement of measurement signals from the converter 14 only when the voltages of amplified photodiode signals from the input amplifier S are above the output voltage of the summing amplifier 30, which in this case represents the positive sum of the output of the third circuit 29 and the reference circuits 11 * The approximate relationships between these voltages may be as shown in Fig. 6b. There, a line indicates the output value 58

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of the reference circuit, a line indicates the output value 59 of the averaging circuit and a line the output value 60 of the summing amplifier, "all referenced to 0V, indicated by the line 61." Each amplified photodiode output signal 57 (electrical detection signal), which is greater than the output value 60 of the summing amplifier ₈ triggers the measuring process. " ¹ These ratios are present throughout the population of the arrangement 18 via the image 56 of the indentation in the direction of the arrow 22 (FIG. 6a), and if the diagonal 62, 62a of the image 56 are parallel extends to the direction of the arrow 22, the length of the image of the diagonals 62 may be determined 62 _$ by the converter 14 of the measuring circuit according to Figo 4a is established as _f that the signal output corresponding to said traversing Bev / ath the arrangement was made (different types and application "Means of converters 14 for the present task have been briefly described in connection with Fig. 2")

In this standard, the Vickers hardness test requires the measurement of the length of the two diagonals of the indentation j which is caused by the pyramidal diamond indenter "The arrangement of FIG _e 6a (in conjunction with the method of illumination according to FIG _e 5c and d.er electronic circuit of FIG _e 4a as written above) represents the currently preferred method for measuring a single diagonal length »Since the diamond impression body is designed as a regular pyramid with a square base area _s are the diagonals perpendicular to each other? when the line of vision relative to the test piece is the same as the direction? If the microscope or another suitable optical

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System of the imaging device is oriented so that the impression is considered in this way, the diagonals are perpendicular to each other in the enlarged image. If, during practical work, the indentation body is printed downwards in the surface of the test specimen in the hormonal direction, the pressure impression only has to be considered in the hormonal direction so that this condition is fulfilled, provided the alignment of the specimen has remained unchanged "6a can measurements of the length of both diagonals be made in the picture of the impression _? if a suitable mount permits rotation through a right angle about an axis perpendicular to the image plane and passing through the center thereof while the device 18 remains in the image plane. "For example, FIG. 3 can be implemented with the device shown in FIG according to which a feed device (displaceable arrangement holder) 63s comparable to the device shown in Fig. 6a is mounted on guides 21 in a housing 64 in which a combined radial and axial bearing 65 covers the entire device on the tube 66 of a microscope 67 or a corresponding optical system which forms an enlarged image 68 of an indentation (not shown) mounted in the surface of a specimen 69.

The microscope 67 bz \ v _o a suitable other optical «system are part of the imaging device of the device» With the other part of the imaging device, the test piece 69 is illuminated. For illumination, electric light sources, or mirrors 671, such as schematically indicated in Pig »7 _? to be used*

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Thanks to the support 65, the housing 64 can be pivoted about a central axis 70 of the microscope 67 in rigid positioning along this axis 70, leaving the photodiode array 18 in the plane of the image 68. The pivoting angle of the housing 64 is limited by a stop plate 71. which is rigidly connected to the tube 66 and has two projections on the circumference 72, which cooperate with a fixed in'dem housing 64 mounted pin 73 to limit the pivot angle of the housing 64 relative to the tube 66 at exactly a right angle angular position of the stop plate 71 relative to the central axis 70 is made so _s that the feed device 63 at a pivot limit of the threaded spindle 23 along the guide 21 in a toward the one diagonal of the enlarged image 68 of the Are jerk parallels direction is controlled at the stop of the housing and when Concerning the other pivoting limit of the housing 64 in a parallel el to the other diagonal of the image 68 parallel directiono

? A further characteristic of the device according to 3 ig _e 7 is the method by which the rotational ™ and the feed movement are performed · For both movements is a single-speed Unikehrelektromotor provided 74; which is rigidly connected to the microscope 67 by means of a support arm 75. The motor 74s, which may be a low-speed motor or a geared, high-speed motor, carries on its drive shaft 77 a pinion 76 o. The pinion 76 operates with a gear 78 large diameter together, which is free to rotate on a radial bearing 79 about the axis 70 of the microscope tube 65 edged in the axial direction but prevented by a (not shown) thrust bearing on a change in position *

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another pinion 80 is attached to one end of a shaft 81 which extends through the housing 64 and is free to rotate in it. The shaft 81 is held in a bearing sleeve 82a. The pinion 80 meshes with the gear 78 and transmits the rotational motion to a bevel gear 82 at the other end of the shaft 81, which meshes with another bevel gear 83 which is mounted on a shaft 84, one end of which is formed as a threaded spindle 23 © The structure is designed so that the torque which must be supplied to the gear 78 to overcome the rotational friction, on the pinion 80, the shaft 81, the bearing sleeve 82aj. the bevel gears 82, 83, the shaft 84 in their (not shown) bearings in the housing 64 and with the (not shown) threaded portion of the feed co-operating threaded spindle 23 occurs, is much greater than data far overcoming the by the rotation of the housing When the motor 74 is energized so that the pinion 76 rotates, thereby rotating the gear 78, the housing 64 and the parts mounted thereon are primarily reversed pivoted the shaft 70 until the pin 73 abuts one of the two projections 72 and thereby prevents further pivoting «Now the engine 74 takes on more power and outputs a higher torque, which then overcomes the Drehreibung ,, which at the parts 76 _S 78, 80, 81, 82 _t 82a, 83 and 84 occurs, and sets the threaded spindle 23 in rotation, whereby the feed device 63 along the Füh 21 is moved in one direction parallel to the one diagonal in your image 68 «.

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When the feed device 63 has arrived in its end position 63a in one direction, it touches a (not shown) microswitch that actuates a (not shown) relay that reverses the motor 74 »Because of the above-mentioned difference in the rotation friction, the housing first 64 pivoted until the pin 73 touches the other projection 72, thus ending the pivoting © ·

The threaded spindle 23 is now driven in the opposite direction, so that the feed device 63 moves in a direction opposite to the previous movement parallel to the other diagonal of the image 68 along the guides 21. In its end position 63b in this direction, the feed device 63 touches a second (not shown) microswitch, which restores the (not shown) relay to its initial state, so that the motor 74 is back in the original direction and the whole working cycle can start again _e In a practical design of the device, it is recommended to install a device which shuts off the supply current for the motor 74 after scanning the two diagonals of the image 68. This shut - off can be done with either of the two mentioned microswitches which actuates a second relay (not shown) which supplies the power supply to the motor Motors 74 interrupts, when the movement of the feed device 63 has reached one of the two end positions 63a _s 63b. Sin (not shown) external switch can then be used to restart the motor 74 and initiate another complete working cycle of the type described. As an alternative to the daa system of microswitches and relays

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for controlling the motor 74 and opto-electronic switching system is applicable, provided that the main specified punctures are exercised ·

In the construction of Fig. 7, there is provided a possible embodiment of the transducer 14 (Fig. 4a) equipped with a gear 85 attached to a shoulder of the shaft 84 and a light emitter / detector assembly 86 comprising a plague body light source and a light detector and that is structured _? that the light source is directed to the detector β When applying a suitable low voltage is increased by an outgoing light beam from the light source 87 of the electrical conductivity of the detector, and a current flows through the conductor S8 _? 89 _s whose other ends are located on a (not shown) Hiederspannungsquelle. Such Smitter / detector assemblies are known and available in trade Yfenn the light beam is interrupted 87 of an opaque object is _s reduced · the conductance of the detector. * And the current flowing in the conductors 88, 89 power is considerably reduced "Mutual Position of the gear 85 and the emitter / detector «arrangement 86 and the dimensions of the teeth on the rim of the gear 85 are chosen so * that the light beam 87 is regulated moderately periodically interrupted? As a result, a uniform periodic sequence of current pulses in the conductors 88 = 89 results directly from the rotational speed of the shaft 84 and thus from the advancing speed of the advancing device 63 which drives the photodiode array 18 over the The current pulse sequence in the conductors 88 _S 89 can then be applied to the gate circuit 13 according to FIG. 4 a, which is determined by means of a suitable measuring circuit 15 in the above-described FIG

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It is important to count only if the image 68 of the impression is detected so that a measurement of the length of the diagonal is made in the image 68.

In the arrangement of Fig. 7, any suitable converter may be employed so that the same arrangement, in conjunction with a compatible measuring circuit 15, offers various possibilities for measuring the diagonal length in the image 68. However, the special configuration of a converter shown in FIG. 7 is particularly well suited in the present application, because the generation of a regular sequence of pulses for transmission to the measuring circuit 15 (FIG. 4a), the application of electronic digital technology in this measuring circuit 15 and in allows the associated circuits to calculate and display the Vickers hardness number from the lengths of the two diagonals expressed in pulse counts. The standard expression for calculating the Vickers hardness can then be converted to

HV. «. 2F sin 68 ° (SS) ²

wherein

F the force applied by the imprint pyramid (kp),

ρ the fixed number of pulses per millimeter feed of the feed device 63s

m is the fixed linear magnification of the image 68 and

η the means of the two pulse counts, which are assigned to the lengths of the two diagonals in the image of the impression,

mean"

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In the field of electronic data processing methods known per se, the value of the Vickers hardness can be calculated from the lengths of the two diagonals in the image 68 in the form of pulse counts, if the values of ρ and m are given and those in the production of the impression applied 'force is measured. In such arrangements, various suitably programmed electronic computers are used, microprocessors tuned to the particular application, and finally dedicated electronic integrated circuits. A digital hardness value output from such an array can be used to feed machines. Automatically sort hardness for these specimens «

The construction of Pig ™ 7 can be used to estimate sinuses in any of the most appropriate illumination modes, but the illumination shown in Fig. 5c is preferred, with zv / ei juxtaposed. The facets of the impression are »timely illuminated *

The figure, Qs. _Figures 8b and 8c show two possible ways in which the facets of the impression can be greatly illuminated and an image as shown in Figure 5c can be obtained. Figure 8a shows a plan view of a system of three exactly '. same light sources 9O _S 91, 92 an imaging device for a hardness tester, the light sources are arranged so that three facets of a Are jerk be illuminated "is disposed within a small region 93 in a surface of a Eärteprüfkörpers, wherein the region 93, the field of view (not drawn ) Microscope in the construction of Fig. 7 represents.

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The three light sources 90, 91, 92 provide similar, substantially parallel illumination beams 94, 95, 96, which may be sequentially turned on to illuminate adjacent facets as previously described.

This is illustrated in Fig. 8b where, in an enlarged view, the impression illuminated by the light beams 94 and 95 is shown. Under illumination by the light beams 94 and 96, the impression appears as in Pig. 8c · The switching of the light sources 90, 91 and 92 in the correct phase to that shown in Fig. 7 system can be effected by any means _s so that measurement of both diagonals can be carried out alternately. For this purpose, devices are suitable for. changing Einsähalten of electric light sources 90, 91, $ 92, or a system of movable diaphragm in permanently switched-held light sources, or, finally, a suitable optical system having at least one movable mirror to align the light beam, as indicated in the Figo 8b and 8c. When using movable diaphragms or mirrors, mechanical or electromechanical actuation aids can be used to maintain the required phase relationships between the illumination system and the measurement system of FIG. 7.

The various systems described so far relate to the estimation of hardness according to the various standard definitions for the determination of Vickers hardness, all based on the above relationship. The standard relationship combines the hardness with the load of the indentor divided by, the square of the median diagonal length. the latter term being twice the surface area elongation of the hardness under pressure

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the condition means that this surface is square as intended. " If the surface size is denoted by A, the hardness relationship becomes in

HV = ff sin 68 °

which is an expression of the mean pressure exerted on the facets at the end of the indentation process

The standard relationship is usually limited in its application to impressions where the edges are reasonably straightforward in the interest of accuracy, but it is possible to apply the above-modified relationship for the less-impressed impression, for example, if the edges are due to "Formation of a raised ridge bent, given that an appropriate method for the accurate determination of the area size of the indentation surface could be found. This is important for the above Bosch friction of the various systems for optoelectronic measurement of the diagonal lengths, because very similar arrangements for measuring the surface area For example, the system shown in Figure 6a could be used for this task if additional lighting were provided to illuminate all four facets of the impression simultaneously brightly could, with an extension of the in Figs. 5a? 5b and 5c would then appear as a square of virtually uniform brightness and any electronic scan of the array 18 would be higher

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Provide signal levels from those photodiodes that lie in the plane of the bright image * ¹

For this purpose, a matched Hessschaltung according to Fig »4a are used for the signal processing, wherein the sample and hold circuit 12-modified and the converter 14 can be omitted. Instead of the converter 14, signals (address signals) from the circuit (not shown) may be used in the sampling circuit of the device ₉ used to drive the photodiode array. In this circuit, a regular, periodically pulsed electronic signal is generated, and the frequency these so-called clock pulses directly determine the speed with which successive photodiodes in the array are addressed. The time interval between successive clock pulses (and thus the idle signals) is thus equal to the time interval between outputs associated with the adjacent diodes of the array, and the sampling time of the overall array is thus determined by the product. from this time interval and the number of diodes in the arrangement ", the threaded spindle 23 of FIG. 6a can be driven by means of a (not shown) motor at a constant speed or with a similar device _s so that the carriage 19 and the assembly located on it 18th at a constant speed over the image of the impression in the direction of the arrow 22 is moved away. The Yorschubgeschwindigkeit can be chosen so large 'that of the assembly 18 during a complete electronic scan through © distance is equal to the dimensional resolution that is required for the measurement of the image of the impression «

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Under these conditions, a stronger signal from any particular photodiode during a given electronic scan of the array 18 may be viewed as a representation of a portion of the bright image of the impression on a substantially rectangular area, the size of which is determined by the product of the dimension resolution and distance values Photodiodes in the array is determined "This area, multiplied by the total number of larger photodiode signals received during the mechanical feed of the array over the magnified image of the indentation, thus provides a measurement for the determination of the total area of the impression."

The measurement circuit of Fig. 4A can be used in the manner described above _s when the sample "and hold circuit 12 is changed such that each discriminator is held from the comparator 10 during a time period" corresponds to the time interval between successive clock pulses during the scan ( d "h" the period between the scanning of one element of the device and the next one). A series of larger photodiode signals has a uniform series of Diskriminatorsignalen from the Kömparator 10 for the sequence _s so that a coherent electronic signal from the sample and hold circuit 12 _s is formed which is used for energizing the gate circuit 13, so the clock pulses or address signals instead of signals "be guided or the measuring circuit 15 · the Gesaratzahl Ή of over the image of the impression counted during a complete mechanical displacement of the arrangement pulses corresponds to the total number of recorded larger Photo" from the converters H in the count diode signals. and it can be used in the occupation

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Psin; 68 ° m ² H? - --- "

.worin Na / m «A = total surface of the impression, m = linear magnification of the image" of the indentation and a = in »incremental surface, given by the product of the dimension projection and the photodiode spacing in the arrangement C

Means comparable to the abovementioned devices can be used to calculate the hardness number H? can be used from the above values * and HV can be automatically displayed as a numerical value »

This method offers several advantages over the method described above, and the possibility of examining impressions with curved side edges is readily apparent. There are also practical advantages, since the measurement requires only a single mechanical feed movement, in which no device is available. Turning the measuring device by 90 ° is required, and the orientation of the feed direction against the impression is not critical. "An additional advantage is that the measurement can be carried out in less than half the time

Instead of linear photodiode arrays _s as · they are used in the system described above, two-dimensional arrangements can be used with numerous parallel-running photodiode row x '· Mechanical devices for the exercise of feed movements are no longer necessary, and give the information

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by electronically scanning all the diodes in the first row one after the other, then all the diodes in the second row and so on until all the photodiodes in the array are scanned. The serial output from such an arrangement can be used in two ways. If a diagonal measurement is required, the output quantity can be added to the circuit according to Pig. 4a, and electronic address signals generated in an off-line circuit and used to drive photodiode arrays one after the other, can be supplied to the gate 13 instead of signals from the previously described transformer 14. The diagonal measurement is then recorded in FIG accumulated in the measuring circle 15 as the number of lines of photodiodes in which a larger signal is produced, because a part of the bright picture of the impression of at least one photodiode is detected in each line. " The diagonal length is the product of the number of such lines and the distance of the center lines of successive lines from each other. The second diagonal measurement can similarly be made after the assembly has been rotated 90 ° about an axis perpendicular to the center of the image plane is, and the hardness number can then be automatically calculated and displayed ·

The other way to use the serial output from a full electronic scan of a two-dimensional photodiode array is exactly the same as that given for the measurement of surface area Δ, except that the array can be held in a fixed position against the image of the impression and The incremental area, a is defined here as the product of the line spacing and the photodiode spacing in each line of the array,

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and these dimensions are practically constant in today's photodiode arrays thanks to the precision of fabrication using photomechanical techniques.

FIG. 9 schematically shows a two-dimensional arrangement 100 and the image 101 of an impression in a specimen surface 102 in an image plane 101a in which the arrangement 100 is located. 103 is intended to symbolize the sampling circuit for the photodiode array.

In a hardness tester designed according to the invention, subjective sources of error during the measurement process are avoided. The use of optoelectronic detection means shortens the measurement duration and substantially increases the measurement accuracy. Structural disturbances on the surface of the specimen in the environment and at the immediate edge of the pyramid impression have no influence on the measurement result.

Claims (4)

209 253 Bringing to mind 1, hardness tester for estimating the dimensions of an impression applied under specified conditions in a surface of a test piece whose hardness is to be tested, from the dimensions of which a hardness value for the test piece can be derived, with an imaging device which is in one Image plane an image of the surface area designs in which the impression is appropriate »characterized by a in the image plane (6a ι 200a; 20a; 54a; 51a; 56a; 101a) attached photosensitive detection device (1,9? 18, 9, 100) which is operable to provide high definition electrical signals representative of brightness hazards within the image of said surface area, and a discriminator circuit (10, 11, 10, 11, 28, 29, 30) incorporating said electrical signals receives and electrical Hachweissignale whose level of brightness in an image area within the image (6; 20; 56; 101) of the impression cha is characteristic, different from signals whose level for the brightness in an image area outside the image (6; 20 \ 565 101) of the impression, ¹ 2, hardness tester according to item 1, characterized in that the imaging device has a lighting device (671; 90; 9I; 92) capable of illuminating the image area with obliquely incident light « 209 25 3 -50- · 12.3.1979 54 569/16 Hardness tester according to item 2, with an indenter in the form of a diamond pyramid with a square base and a half angle of 68 ° and a device for pressing the indentor in the surface of the specimen, whereby said impression is formed with a complementary to the shape of the indent body pyramid shape, characterized in that the illumination device (671 »90, 91» 92) is arranged so that the illuminating light emanating from it is reflected by at least one of the facets (37-47 »52) of the impression normal to the surface of the specimen · Hardness tester according to item 1, 2 or 3, characterized in that the photosensitive detection device comprises a single photosensitive element (1, 201), and in that a scanning device (2, 3 * 4? 55 202, 203, 204s 205). is provided which performs a scanning relative movement between the single photosensitive member (1 j 201) and the image (6} 200) of the surface area in which the imprint is applied when the apparatus is used for the estimation of dimensions of the indentation. Hardness tester according to item 1 * 2 or 3? characterized in that the photosensitive ITacheinrichtung comprises a one-dimensional array (18) of photosensitive elements * ¹ and that the apparatus further comprises a scanning device (18a, 19, 21, 23, 24, 25; 21, 23 * 70 to 84), the when using the device for assessing the dimensions of the impression a perpendicular to the straight-line arrangement (18) extending between the Abtastrelativbewegung assembly (18) and the image (20) of the surface area in which the Sinruck is attached manufacturer _{s β} 209 25 3 -51- 12.3.1979 54 569/16 beiführt. 6. Hardness tester according to item 1, 2 or 3 # marked •. in that the photosensitive detection device has a two-dimensional arrangement * (100) of photosensitive elements * 7 · hardness tester according to point 4? characterized in that the scanning device is a tongue (2) with the photosensitive member (1) at its one end, further a tongue holder (3 "4) * to which the other end of the tongue (2) is fixed and the rectilinear in the manner is movable, that the photosensitive member (1) over the image (6) of the surface region in which the sensation is attached, and a device having said one end of the tongue (2) transversely to the said direction of movement and let it swing " 8 * hardness tester according to point 4? characterized _s that said scanning a movable support (202 to 205) _f at which the individual light-sensitive element (201) fixed and rectilinear be in the way ~ is wegbar? that it is passed over the image of the surface area in which the impression is made, * and an opto-mechanical device (19S ₅ 195) _s the said image (200) across the photosensitive element (201) transversely to said direction of movement swinging back and forth / 9e hardness tester according to item 8, characterized in that the opto-iiiechanische device a mirror (196) on. indicates * the sum can be brought swinging and on the » -52- 12.3.1979 54 569/16 the way that said image (200) moves back and forth, 10v hardness tester according to item 5 », characterized in that the scanning device has a support (19» 63) for the arrangement (18) movable perpendicular to the linear extent of the arrangement (18) and a scanning circuit (118a) which extracts the detection signals from the respective ones derived photosensitive elements of the arrangement (18), wherein the elements for generating the Ifachweissignsle be scanned in cyclic repeated order successively 11. Hardness tester according to item 6, characterized by a scanning circuit (103) »deriving the liachweissignale of the respective photosensitive elements of the arrangement (100), wherein the elements of each line of the array in turn successively and the rows of the arrangement (100) of Sequentially sequentially scanned in cyclically repeated sequence. 12. hardness tester according to item 7 »8, 9 _f 10 or 11, characterized in that the discriminator circuit comprises a comparator (10) which receives the liachweissignale and compares the received Lachweissignale with a comparator supplied threshold signal and according to the results of comparison comparison signals gives? which is either a first level level indicative of an illicit signal characterizing the brightness in an image area within the image (6, 20, 56, 101) of the indentation, or a second level height s indicative of the detection signal the brightness in an image area outside the image (6, 20, 56? 101) of the image 209 25 3 -53- 12.3.1979 54,569 / 16 and that the discriminator circuit further comprises a sample and hold circuit (12) receiving the comparison signals and responsive to the comparison signals having said first level level for outputting a sample output signal of a predetermined level after fading level signal equal to a half period of the relative vibration between the image and the photosensitive member (1, 201) according to claim 7 »8 or 9 or equal to a whole scanning period of the assembly (18) according to Is point 10 or equal to the time required to scan one line of the array (100) according to point 11 A hardness tester according to item 12, characterized by the provision of a gating circuit (13) connected to the sample and hold circuit (12) for receiving the sampling output signal and detecting measurement signals generated in the device and as appropriate characteristic of movements of the movable support (3 * 4, 202 to 205) according to item 7, 8 or 9 or for movements of the movable assembly support (19 s 63), see item 10 or for the respective successive scans of the assembly (18) according to item 10 or for the scanning of respectively successive rows of the arrangement (100) according to item 11, and which further forwards those measuring signals into a measuring circuit (15) of the apparatus only if said scanning output signal is the selected value 209 253 -54- 12.3.1979 54 569/16 The hardness tester according to item 12, characterized in that the discriminator circuit has a further gate circuit (28) which receives the detection signals and the comparison signals, which forwards the detection signals if the comparison signals have the second level level, and an averaging circuit (29). which receives the detection signals relayed by the further gate circuit (28), and a summing circuit (30) which receives a reference level signal generated in the discriminator circuit and an averaged signal from the averaging circuit and the comparator (10) the sum of the reference level signal and the averaged signal as Threshold signal forwarded 15 * hardness tester according to item 10 or 11, characterized in that the discriminator circuit comprises a comparator (10) which receives the detection signals and the received detection signals with a the comparator. Compares (10) supplied threshold signal and outputs according to the results of the comparison comparison signals having either a first level level indicative of a detection signal representing the brightness in an image area within the image (6, 20, 56, 101) of the indentation or a second level level indicative of the detection signal characterizing the brightness in an image area outside the image (6, 20, 56, 101) of the indentation, further comprising a sample and hold circuit (12) receiving the comparison signals and responsive to the first level height comparison signals for outputting a sample output signal of predetermined magnitude that is set to "-" during a period of time. 9 25 3 - ⁵⁵ - 12.3.197? 54 569/16 which is equal to the transit time between the scanning of a single element of the device (18, 100) and the next, and finally a gate circuit (13) connected to the sample and hold circuit which picks up the sampling output and further receives address signals generated in the sampling circuit (118a, 103) to scan the respective elements of the array (18, 100), a single element of the array (18, 100) providing a check signal whenever the array is supplied with an address signal which will eventually supply those address signals to a counter (15) of the device only if the sample output signal has the selected value * ! 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