JPH0257659B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an improvement of a constant force hardness tester for measuring the hardness of an elastic body such as rubber, and particularly takes into consideration the stress relaxation phenomenon of the elastic body. This invention relates to a constant force digital hardness tester that can automatically read the hardness of a material and display the measured value digitally.

[Prior art] Olsen type hardness tester in Section 5.3 of JIS K6301, Pousey-Gyons type hardness tester in Section 5.4, or
For measuring international rubber hardness (IRHD) as specified in ISO48-1979, any of the commercially available constant force hardness testers are designed to measure the international rubber hardness (IRHD) specified by ISO 48-1979. First, a primary load (including the weight of the pusher needle, etc.) is applied in the direction, and then a specified secondary load is applied, and the amount of vertical movement of the pusher needle during that time is converted into rotation amount by the rack and pinion mechanism. However, a dial gauge system was used in which the scale on the gauge board was read by the movement of the indicator needle on the analog gauge board.

This method is characterized by its relatively simple structure and low cost, but on the other hand, it has the following drawbacks. One of them is that after applying the primary load and before applying the secondary load, it is necessary to set the dial gauge to the zero position, and for this purpose, the scale plate of the dial gauge must be rotated. There was a problem that I had to do it.

In addition, these constant force hardness testers are usually specified to read the hardness after a certain period of time (for example, 30 seconds) has passed after applying a static load.
When measuring materials with large stress relaxation whose hardness indication changes over time, it is difficult to read the position of the moving pointer while keeping time, which results in inaccurate measurement results. There was a problem that the dispersion of the data became large.

Furthermore, the conventional mechanism that uses a rack and pinion to convert the vertical movement of the indenter into rotational movement is prone to looseness and friction, and because it is small, it cannot obtain a sufficient amount of rotation, which reduces measurement accuracy. There was also the problem of lowering the

On the other hand, in a micro hardness tester for micro test pieces specified by ISO48, the indenter travel distance is as small as 0.3 mm on a full scale, and in order to read the hardness from the indenter travel distance, a dial gauge is used. However, it is difficult to directly read the needle accurately, and efforts have been made to increase the amount of movement of the indenter (Co., Ltd.).
(Hiraizumi Yoko Catalog, manufactured by Wallace, UK) These mechanisms had the drawbacks of being complex, cumbersome to operate, and expensive.

A conceivable way to solve these problems is to electrically detect the amount of movement of the indenter and convert it into a digital signal. As a means for this purpose, digitization of the measured values of spring-type hardness meters has already been published in Japanese Patent Publication No. 55-20191 and Japanese Patent Application Laid-Open No.
56-153235, JP 57-184949, JP 58-9044, JP 58-72032,
Utility Model Application Publication No. 59-20146 has been reported,
These methods include a method using a rotary encoder, a method using a variable resistor, a method using a differential transformer, and a method using a linear scale using a single slit plate, all of which have problems.

For example, in the rotary encoder method, vertical movement must be converted into rotational movement using a rack-and-pinion mechanism, so similar to the conventional dial gauge method, this converting part causes measurement accuracy problems, and then a computer etc. No matter how well the analysis is carried out, the hardness of the sample being measured cannot be accurately measured, and the conventional problems have not been solved.

On the other hand, the method of digital conversion using a variable resistor involves contacting the resistor with the amount of vertical movement of the push needle and converting the amount of change into an electrical signal.
This method not only cannot accurately detect the small amount of vertical movement of the indenter due to the friction caused by contact, but also the detected electrical resistance is an analog value, and it cannot be converted into a digital meter without converting it from analog to digital. As a result, the hardness meter has a large number of components, which poses a major problem: not only is the measurement accuracy poor, but the hardness meter is large and expensive.

In addition, the differential transformer method converts electrical quantities into analog/
It requires digital conversion, and like the variable resistor method, the hardness meter itself has the problem of being large and expensive. These large hardness testers cannot be powered by batteries from the point where they require power, so they cannot be carried anywhere, and they also have other problems such as being susceptible to power fluctuations and electrical noise. have.

In addition, in devices that use a linear scale with a single slit plate, the movement of the slit is read by an optical sensor across the single slit plate, so magnification is required to detect minute displacements of the indenter. This method requires a device, and the hardness tester itself becomes large and expensive, or if a magnifying device is not used, the accuracy is poor.

In addition, regarding the digitalization of the measured values of constant force hardness testers, we have developed a system using a differential transformer for automatic measurement of Bitkers hardness and Brinell hardness.
12455, JP-A-57-20642, JP-A-57-148233, Utility Model Application, JP-A-57-14823, which determines the hardness of the material by automatically measuring the area of the indentation using a television camera or an optical microscope. Publication No. 177157 or JP-A-59
-18651 has been reported, but none of these is a method for determining hardness from the amount of movement of the indenter.

[Purpose of the invention]

The present invention was developed as a result of studies to solve the above-mentioned problems.

Therefore, an object of the present invention is to obtain not only highly accurate hardness measurements but also the degree of dispersion of the sample by devising a way to directly detect the amount of vertical movement of the indenter using a linear encoder. Our goal is to provide an excellent digital hardness meter that can

[Structure of the invention]

In other words, the present invention applies a constant load to the surface of a flexible material via an indenter of a certain shape, and determines the depth of penetration (amount of movement) of the indenter into the material at that time.
is the hardness of the material, and is provided with a linear encoder for detecting the amount of movement of the indenter, and this linear encoder is attached to a movable slit plate that interlocks with the indenter, and to a position opposite to the movable slit plate. A light-emitting element and a light-receiving element are provided at positions opposite to each other with a fixed slit plate placed between them. A change in brightness caused by the movement of the moire stripes is converted into an electrical signal so that it can be detected, and a control circuit is connected to the linear encoder that can convert the electrical signal into a pulse and digitally display the amount of movement of the presser needle. The gist of this invention is a constant force digital hardness tester characterized by the following characteristics.

〔Example〕

Hereinafter, the present invention will be specifically described by way of examples with reference to the drawings.

FIGS. 1 to 7 show a constant force digital hardness tester according to an embodiment of the present invention, FIG. 1 is an explanatory front view with main parts cut away, and FIG. 2 is an explanatory front view showing the external appearance of the same. 3 is a vertical cross-sectional explanatory view showing the main parts of the same as above, that is, the internal structure of the linear encoder, FIG. 4 is a cross-sectional explanatory view of the same as above, and FIG. ,
FIG. 6 is an explanatory diagram of operating waveforms of the direction determining circuit used in the present digital hardness meter, and FIG. 7 is a block explanatory diagram showing the configuration of the present digital hardness meter.

In the figure, 1 is a base, and a vertical arm 3 is attached to a column 2 erected vertically on one side of the upper surface of the base 1.
is installed. And this lifting arm 3
is equipped with a lifting mechanism (using a rack and pinion, for example), so that it can be moved up and down along the column 2 by turning the handle 4 by hand.

Note that the lifting arm 3 can also be automatically operated by rotating the handle 4 using a motor or the like.

Further, a holding tube 5 is provided in front of the lifting arm 3, and a spindle 6, a load 7, and a pressure leg 8 are installed coaxially inside the holding tube 5. There is a pusher needle 9 at the lower end of the spindle 6, and circular projections 6 ₁ and 6 ₂ are fixed to the middle and top parts of the pusher needle 9, respectively, and a load 7 is applied between the two projections. It is provided.

The holding tube 5, the spindle 6, the load 7, and the pressure leg 8 are configured to be able to freely slide vertically relative to each other, and a linear encoder is provided between the spindle 6 and the pressure leg 8. 10 is included.

The sample stage 12 on which the sample 11 is placed is located directly below the spindle 6 and is provided integrally with the base 1.

In the above structure, the tip of the indenter 9 is connected to the sample 11.
The positional relationship of each component of this hardness tester when separated from the hardness meter is as shown in FIG. That is, (a) the flange 7 ₁ formed on the upper part of the load 7;
The lower surface of the holding tube 5 rests in contact with the upper surface of the holding tube 5.

(b) Further, the lower surface of the protrusion 6 ₂ located at the top of the spindle 6 rests on the upper surface of the load 7 .

(c) Furthermore, the pressure leg 8 has its intermediate flange 13
The lower surface of the holding tube 5 rests on the upper surface of the lower flange ₅₁ of the holding tube 5.

(d) At this time, the pusher needle 9 at the tip of the spindle 6 projects slightly downward from the center hole 8 ₁ on the lower surface of the pressure leg 8 .

When the lifting arm 3 is lowered from this state by operating the handle 4, the tip of the indenter 9 first comes into contact with the upper surface 11a of the sample 11, and the upper surface of the load 7 and the lower surface of the top protrusion ₆₂ are separated. . When the lifting arm 3 is further lowered, the lower surface 8 ₂ of the pressure leg 8 touches the sample 1.
1, and the intermediate flange 13 of the pressurizing leg 8 and the lower flange ₅₁ of the holding tube 5 are separated from each other.

In this state, a static load due to the weight of the spindle 6 and pusher needle 9 is applied to the measurement point on the upper surface 11a of the sample 11.
It acts as a primary load, and at the same time a pressure surface load due to the weight of the pressure leg 8 acts on the annular surface around the measurement point.
The conditions around the measurement point are kept constant.

When the lifting arm 3 is further lowered, the load 7
The lower surface 7 ₂ of the load member 7 contacts the upper surface of the intermediate projection 6 ₁ , and as a result, the outer periphery of the lower surface of the upper flange 7 ₁ of the load 7 separates from the upper surface of the holding tube 5 . In this state, in addition to the primary load, a static load due to the weight of the load 7 acts as a secondary load at the measurement point of the sample 11.

In other words, in the above-mentioned process, the initial state is the state in which the primary load is applied, and the amount by which the spindle 6 moves downward when the secondary load is applied thereafter varies depending on the hardness of the sample 11, so this amount of movement By reading this, the hardness of the sample 11 can be measured.

The linear encoder 10 has a built-in mechanism and circuit for extracting the amount of movement of the spindle 6 as a digital signal, and this digital signal is processed by a circuit built into the display/operation section 14 shown in FIG. , is displayed on the hardness display 15 as a hardness value.

Next, the configuration of the linear encoder 10 will be explained with reference to FIGS. 3 and 4.

This linear encoder 10 includes a movable slit plate 16 fixed to a spindle 6 and moving linearly in the axial direction of the spindle 6, a fixed slit plate 17 fixed to the main body of the linear encoder 10, a movable slit plate 16 and a fixed slit plate. Two sets of light emitting elements 18, 18' placed before and after 17, and light receiving elements 19,
19' and a voltage comparator 20.

The slit plates 16 and 17 are transparent plates with thin opaque lines printed at regular intervals, and the lines of the movable slit plate 16 and the fixed slit plate 17 overlap each other depending on the upper and lower positions of the spindle 6. They no longer overlap at all, but rather overlap. Then, changes in brightness and darkness due to the degree of overlap between the lines are detected using an approximate sine wave 3 by the light receiving elements 19 and 19'.
After converting it into a zero electrical signal and extracting it, the voltage comparator 20 further shapes the waveform into a rectangular wave 31.

Note that the slits of the movable slit plate 16 and the fixed slit plate 17 may not be completely parallel, and there may be a slight inclination between them. (In this case, both may be tilted in opposite directions with respect to the horizontal line, but one of them may be made horizontal and the other tilted with respect to the horizontal line.) In this case, the spindle 6 can be moved to make it movable. When the slit plate 16 is moved in the vertical direction, dark and light stripes called moiré stripes as shown in FIG. 5 move left and right. Even in this case, if the pitch of the moire fringes is larger than the diameter of the light-receiving element, the change in brightness due to the movement of the shading of the moire fringes can be detected by the light-receiving elements 19, 19'.
After converting it into an electrical signal of an approximate sine wave 30 and extracting it, the voltage comparator 20 further shapes the waveform into a rectangular wave 31.

In this case, the slight inclination between both slit plates means that, for example, if the size of the light receiving element is 4 mmφ, two stripes will be detected in one element unless the interval S between the moiré fringes is 4 mm or more. .

Generally, if the pitch of the slit is d and the angle of inclination is α, the interval S of the moiré fringes is given by S≒d/α, so when reading the hardness to the nearest 0.05 using the Olsen hardness meter , the interval d between the slit lines is 0.005 mm, and when the interval between moire fringes is 5 mm, the inclination angle α = d/s = 0.005
mm/5mm=0.001rad (1rad=57 degrees), and similarly when reading up to 1 unit of hardness, 0.1/5=
It becomes 0.02rad.

These numbers depend on the dimensions of the element, but the inclination angle of the slit is usually selected in the range of 0.001 to 0.02 rad according to the measurement accuracy. In addition, in order to read the hardness value in units of 0.05 degrees, the interval d between the slit lines is set to 0.00125 mm x 4 = 0.005 mm using the quadruple pulse described later.
It is necessary to set the pitch interval (d) to .

Further, in the micro hardness tester mentioned above, hardness values can be read to the nearest 0.5 degree by using the quadruple pulse.

By counting the number of rectangular waves obtained in this manner, the amount of movement of the spindle 6 can be measured.

Furthermore, in order to recognize the moving direction of the spindle 6, the set of elements 18 and 19 and the set of elements 18' and 19' are positioned at a certain distance apart.
The line of one of the slit plates sandwiched between the elements of one set is shifted from the line of the same slit plate in front of the other set of elements so that their output phases differ by 90 degrees from each other.

Due to this deviation, A from the pair of elements 18 and 19
The moving direction can be determined by outputting B-phase signals whose phases are different from each other by 90 degrees from the pair of phase elements 18' and 19'.

FIG. 6 is a waveform diagram showing the operating procedure of a circuit for determining the moving direction of the spindle 6. The linear encoder 10 outputs two signals (A
phase and B phase) are output. FIG. 6 shows waveforms when the spindle 6 is raised and lowered.

Next, a differentiating circuit is used to generate an A-phase rising timing pulse At and an A-phase falling timing pulse shown in FIG. FIG. 6 shows the logical product At×B of the timing pulse At and the B phase, and the logical product×B of the timing pulse and the B phase. If both signals of this logical product are inputted to an RS flip-flop, the output will be as shown in FIG. 6, so that the direction of rise and fall of the spindle 6 can be determined.

Further, by taking the logical sum of the logical product and the logical product, the counting pulse shown in FIG. 6 can be extracted.

Furthermore, using the inversion of the B phase, At in Fig. 6 2,
If you combine it with , you will get twice as many pulses. Further, by combining this double pulse, the rising and falling pulses of the B phase, and the double pulse obtained by inverting the A phase and the A phase, a quadruple pulse can be obtained.

FIG. 7 is a circuit diagram of the embodiment shown in FIG. As shown in FIG. 7, the linear encoder 10
The displacement signal outputted from the display operating section 14 is displayed on the hardness display 15 through a direction discrimination circuit 21, a reversible counter 22, a time control circuit 23, and a display control circuit 24.

The direction discrimination circuit 21 inputs the two signals of A phase and B phase from the linear encoder 10, and generates a number of pulses proportional to the displacement of the spindle 6, that is, the amount of movement, along with a discrimination signal for raising or lowering the spindle 6. It is output and sent to the next reversible counter 22.

The reversible counter 22 counts the number of pulses and outputs the amount of movement of the spindle 6 in the form of a binary number, for example, and increases or decreases the count output signal depending on the direction discrimination signal. Time control circuit 23
is a stress relaxation phenomenon that is usually observed when measuring the hardness of a measured sample, that is, the hardness value shows the highest value immediately after applying a secondary load to the sample, and then the hardness value gradually decreases and finally becomes almost stable. For a phenomenon that is a value,
It has a peak hold circuit that holds the maximum value, and a circuit that determines which period of time the value is to be the hardness value of the sample to be measured, and for example, indicates the maximum value,
Alternatively, after the set time has elapsed, the display on the hardness indicator 15 maintains the value at that time. In this case, the time signal setter 25
If you enter a set time in advance in , after the maximum hardness value is obtained, the hardness value after the set time has elapsed can be held and displayed.

The display control circuit 24 converts the hardness data signal (for example, a binary data signal) from the time control circuit 23 into a form that can be displayed on a display, and includes a decoder, a multiplexer, and the like.

The hardness display 15 is composed of, for example, a 7-segment light emitting diode (LED) (or liquid crystal [LED]) numeric display with 3 to 4 digits. Note that this display can be switched and used as an input signal display for the time signal setting device 25 described above, or as an input signal display for the pass/fail criterion setting device 27 described later.

In addition, the display operation section 14 includes a pass/fail determination circuit 26 that determines whether the measured hardness value is within a preset tolerance range. This compares the measured hardness value with a reference hardness value inputted in advance to the pass/fail judgment standard setter 27, and outputs the result to the pass/fail judgment display 28. In this case, an upper limit, a lower limit, and an upper and lower limit can be set for the reference hardness value depending on the purpose. As an example of the pass/fail judgment indicator 28, a means may be used in which LEDs are individually lit to light up when the measurement result exceeds the upper limit or lower limit of the allowable range.

Furthermore, the display/operation section 14 can be provided with a function of sending measurement results to an external data processing device (for example, a printer, a microcomputer, etc.). In this case, it is preferable to provide versatility by, for example, converting the measurement results into binary coded decimal numbers (BCD) using the signal converter 29, if necessary.

Note that the time control circuit 23 and subsequent parts in FIG. 7 can be configured by hardware as shown in the figure, but they can also be configured by software using a microcomputer.

The display operation unit 14 is separated from the hardness meter of the present invention,
It may also be held as an external function in combination with an external data processing device. In that case, there is an advantage that the hardness value can be obtained simultaneously with the external data processing results. Furthermore, if the display operation section 14 is separated from the main body, all functions other than the linear encoder 10 shown in FIG. 7 will be retained as external functions.

If the digital hardness meter of the present invention as described above is used to directly detect the amount of vertical movement of the indenter using a linear encoder, there will be no mechanism to convert the vertical movement into rotational movement, and this will prevent backlash and friction of each part. Since the influence of

In particular, when glass is used for the slit of a linear encoder and the scale is made by vapor-depositing chromium on the glass, it is possible to optically detect displacements up to about 1 μm, making it possible to detect displacements with extremely low error and high precision. It becomes possible.

If such a high-precision linear encoder is used in a constant force hardness meter, and if a means is used to keep the temperature etc. constant during measurement, it will be possible to read ±1 degree from the analog value, which is the minimum unit of hardness values. What I was doing was
It varies depending on the type of hardness meter, but from ±0.5 degrees to ±
Hardness values up to 0.05 degrees can be accurately obtained as digital values, increasing accuracy by up to 20 times. Of course, it is easy to lower the accuracy depending on the purpose.

〔Effect of the invention〕

Since the present invention is configured as described above, the hardness of a sample can be measured with high accuracy and extremely easily. As a result, it is possible to easily examine, for example, the distribution of the vulcanization state of vulcanized rubber and the dispersion state of mixed ingredients, which could not be measured with conventional hardness meters.

Furthermore, since the present invention can directly count pulse signals from a linear encoder as digital values, there is no need for electrical conversion means such as an A/D converter, and furthermore, the above-mentioned mechanical conversion means, such as those specified by ISO48, are not required. In a micro hardness tester for micro test pieces, the hardness of a sample can be accurately detected without using a mechanism to magnify the amount of movement of the indenter. As a result, the hardness meter body has been made smaller and
It is lightweight and easy to carry,
Moreover, since a battery can be used as a power source, there is no fear that the measurement results will be abnormal due to electrical noise, and it can be used anywhere with peace of mind.

In addition, this constant force digital hardness tester can automate its load loading device, extend the tip of the indenter to enable measurement of samples inside a thermostatic oven, and compare measurement results with standard hardness values. By using the pass/fail judgment function in the test, combined with the digital display and printout function, it is much easier to use than conventional ones, and is effective for sample development research and in factories. It can be used for.

[Brief explanation of the drawing]

FIGS. 1 to 7 show a constant force digital hardness tester according to an embodiment of the present invention, FIG. 1 is an explanatory front view with main parts cut away, and FIG. 2 is an explanatory front view showing the external appearance of the same. 3 is a vertical cross-sectional explanatory view showing the main parts of the same as above, that is, the internal structure of the linear encoder, FIG. 4 is a cross-sectional explanatory view of the same as above, and FIG. ,
FIG. 6 is an explanatory diagram of operating waveforms of the direction determining circuit used in the present digital hardness meter, and FIG. 7 is a block explanatory diagram showing the configuration of the present digital hardness meter. 9... Push needle, 10... Linear encoder, 16
...Movable slit plate, 17...Fixed slit plate,
18, 18'... Light emitting element, 19, 19'... Light receiving element.

Claims (1)

[Claims] 1. Hardness when a fixed load is applied to the surface of a flexible material through a pusher needle of a certain shape, and the depth (amount of movement) of the pusher needle into the material at that time is the hardness of the material. A linear encoder is provided to detect the amount of movement of the indenter. The light-emitting element and the light-receiving element are arranged opposite to each other, and the light-emitting element and the light-receiving element are arranged to face each other. The constant force digital hard drive is configured such that the linear encoder is connected to a control circuit capable of converting the electric signal into a pulse and digitally displaying the amount of movement of the pusher needle. Total.