Abstract:
A measurement cylinder having a passage for an indenter hammer to go forward and backward formed therein is provided with two light receiving holes a distance S apart. The times required for the indenter hammer to go past the light receiving holes are measured and, in accordance with the required times measured and the distance S, the impacting velocity and the rebounding velocity of the indenter hammer are detected, whereby it is made possible to greatly improve the detecting accuracy of both the velocitys.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an Equotip type hardness tester in which an indenter hammer is caused to impact against a specimen and the hardness of the specimen is measured from the ratio between the velocitys of the indenter hammer before and after the impaction.  
           [0003]    2. Description of the Related Art  
           [0004]    A rebound type hardness tester, in which an indenter hammer is caused to impact a specimen and the hardness of the specimen is calculated from the ratio between the velocity of the indenter hammer immediately before the impaction (impacting velocity) and the velocity of the same immediately after the impaction (rebounding velocity), is generally called an Equotip type hardness tester and put to practical use.  
           [0005]    Since the indenter hammer in the Equotip type hardness tester is adapted to be shot by means of a coil spring, it is not necessarily required, in hardness measurement, that the Equotip type hardness tester is set in the position to keep the impacting direction straight down. Namely, it is possible to carry out the hardness measurement with the Equotip type hardness tester (the body  1  formed of a cylindrical handle portion  11  and a measuring cylinder  12  connected to it) tilted, i.e., keeping the impacting direction, for example, in the horizontal direction, in an angle of depression of 45°, in an angle of elevation of 45°, and in the direction straight up (the angle of inclination then formed between the body  1  and the horizontal plane  010  is denoted by 0) and with the front end of the measuring cylinder  12  abutting on the specimen  01  as shown in FIG. 3. Thus, such an advantage is obtained that hardness of the side face or bottom face of a specimen can be freely measured.  
           [0006]    The indenter hammer  3  is adapted to be discharged in the axial direction of the body  1  guided by the cylindrical body  1 . Further, there are provided a permanent magnet within the indenter hammer  3  and a velocity detecting coil  4  wound around the front end portion of the measuring cylinder  12 , and, by the movements of the permanent magnet (i.e., the indenter hammer  3 ), electric currents proportional to the impacting velocity and the rebounding velocity are caused to flow through the velocity detecting coil  4 . The currents are converted into voltages by a voltage transformer  5  within a display unit  6 , the voltages are input to a CPU  7  to calculate the hardness, and the calculated value is displayed as the Equotip hardness L of the specimen on a display  8 . The Equotip hardness L is defined by a later described expression (1).  
           [0007]    The velocity impaction the specimen  01  of the indenter hammer  3  when hardness is measured with the body  1  tilted is different from its velocity produced when the body  1  is held in the upright position. Therefore, it has so far been practiced to obtain the correct hardness value by checking the value (hardness) of the result obtained by the tilted measurement with a table (conversion table) for angular correction. There is such a one put to practical use that automatically performs the angular correction by means of an incorporated CPU. Further, there is also such a one put to practical use that automatically converts an obtained hardness value into a standardized hardness value so far in use (e.g., Brinell, Vickers, Rockwell C, and Shore hardness) and displays the hardness value.  
           [0008]    The principle of measurement in the Equotip type hardness tester will be described with reference to FIG. 4. Referring to FIG. 4, reference numeral  3  denotes an indenter hammer and  01  denotes a specimen. The indenter hammer  3  is shot by a coil spring (not shown) incorporated in the measuring cylinder  12  to impact the specimen and then rebound from the same.  
           [0009]    At this time, if friction and air resistance against the indenter hammer  3  in motion is neglected and it is assumed that no external force other than the gravitational force acts on the indenter hammer  3  after it has been discharged, the hardness L of the specimen  01  is defined by the following expression  
             L= (| V   2   |/|V   1| )×1000  (1)  
           [0010]    where  
           [0011]    V 1 : impacting velocity of the indenter hammer,  
           [0012]    V 2 : rebounding velocity of the indenter hammer.  
           [0013]    In the conventional Equotip type hardness tester, detection of the velocitys of the indenter hammer  3  (the impacting velocity against and rebounding velocity from the specimen  01 ) is performed by measuring voltages produced in the coil at the time when the permanent magnet incorporated in the indenter hammer  3  passes by the velocity detecting coil,  
           [0014]    Generally speaking, the voltage change occurring in the velocity detecting coil (in pulse waveform) varies with the velocity at which the permanent magnet passes by the coil. Namely, the slower the passing velocity of the permanent magnet, the duller becomes the pulse waveform W (as shown by dotted lines in FIG. 5). From this, a problem arises that accurate measurement results cannot be obtained.  
           [0015]    Further, there is also such a problem that when the specimen is a magnetic body or it is magnetized or the environment is magnetized, an accurate result of measurement cannot be obtained due to the effect of such magnetism.  
         SUMMARY OF THE INVENTION  
         [0016]    It is an object of the invention to provide a method of detecting velocitys of the indenter hammer in an Equotip type hardness tester whereby the above mentioned problems are solved and an Equotip type hardness tester in which the aforesaid detecting method is carried out.  
           [0017]    As the means for solving the above problems, a method according to the invention of detecting velocitys of an indenter hammer in an Equotip type hardness tester, including a measuring cylinder constituting the body of the hardness tester and providing a passage for the indenter hammer to go forward and backward, the measuring cylinder having two light receiving holes formed therein a distance S apart in the axial direction thereof, comprises the steps of measuring the times required for the indenter hammer to go forward and backward past the two light receiving holes and detecting the velocitys of the indenter hammer in accordance with the required times and the distance S.  
           [0018]    As the means for solving the above problems, the required times are calculated by having a pulse counter, to which timing pulses generated by a pulse generator are input, count the number of the timing pulses from the moment of receipt of a signal indicating that the indenter hammer passed by one light receiving hole of the two light receiving holes to the moment of receipt of a signal indicating that the same passed by the other light receiving hole.  
           [0019]    As the means for solving the above problems, an Equotip type hardness tester according to the invention comprises a measuring cylinder constituting the body of the hardness tester and providing a passage for an indenter hammer to go forward and backward, a coil spring incorporated in the body, an indenter hammer adapted to be shot by the spring force of the coil spring toward a specimen, a velocity sensor attached to the body for measuring the velocitys of the indenter hammer immediately before impacting against the specimen and immediately after the impaction, and a display unit including a CPU receiving information of the velocitys of the indenter hammer detected by the velocity sensor for calculating hardness of the specimen and a display for displaying thereon the hardness of the specimen calculated by the CPU, wherein the velocity sensor is constituted of two light projecting holes formed in the vicinity of the front end portion of the measuring cylinder a distance S apart from each other in the axial direction of the measuring cylinder and light receiving holes formed in the positions corresponding to the light projecting holes, and, further, light sources provided for each of the light projecting holes and photodetector devices provided for each of the light receiving holes.  
           [0020]    In the invention, the indenter hammer, at the time of measurement, passes by the two light receiving holes formed a distance S apart in the axial direction of the measuring cylinder in the order of the inner light receiving hole and the outer light receiving hole in the impacting course, whereas it passes by them in the order of the outer light receiving hole and the inner light receiving hole in the rebounding course after impacting against a specimen.  
           [0021]    Hence, by measuring the time required for the indenter hammer to pass by the light receiving holes in the impacting course and the time required for the same to pass by the light receiving holes in the rebounding course, the impacting velocity against and the rebounding velocity from the specimen (face) of the indenter hammer can be calculated in accordance with the measured times and the distance between the light receiving holes.  
           [0022]    The aforesaid times can be calculated by using a pulse counter and by having numbers of timing pulses counted by the pulse counter.  
           [0023]    Further, since the indenter hammer velocity (detecting) sensor is provided by that of a photoelectric type, it is made possible to carry out the detection having the detecting accuracy of the velocity of the indenter hammer unaffected by the indenter hammer velocity.  
           [0024]    Further, the measurement can be carried out unaffected by magnetism.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a diagram schematically showing a sensor portion of velocitys of an indenter hammer in an Equotip type hardness tester as an embodiment of the invention.  
         [0026]    [0026]FIG. 2 is a circuit diagram of a velocity detector circuit of the indenter hammer.  
         [0027]    [0027]FIG. 3 is a diagram schematically showing a conventional Equotip type hardness tester.  
         [0028]    [0028]FIG. 4 is a diagram schematically showing the measuring principle in the Equotip type hardness tester.  
         [0029]    [0029]FIG. 5 is a pulse waveform in a conventional velocity detector portion.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    A method of detecting velocitys of the indenter hammer in an Equotip type hardness tester as an embodiment of the invention and an Equotip type hardness tester in which the aforesaid detecting method is carried out will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the sensor portion of velocitys of the indenter hammer and FIG. 2 is a circuit diagram of the detector circuit of the indenter hammer velocitys. Reference numerals in FIG. 1 and FIG. 2 like those in FIG. 3 and FIG. 4 denote virtually the same members.  
         [0031]    In the embodiment of the described type, a set of light projecting holes  1   a  and  2   a  constituting the sensor of the velocitys of the indenter hammer  3  (impacting velocity against and rebounding velocity from the specimen  01 ) are provided in the vicinity of the front end portion of the measuring cylinder  12  a distance S apart in the axial direction of the measuring cylinder  12  as shown in FIG. 1.  
         [0032]    Further, in the positions of the measuring cylinder  12  opposing the light projecting holes  1   a  and  2   a , there are provided a set of light receiving holes  1   b  and  2   b  the same distance S apart.  
         [0033]    The light projecting holes  1   a  and  2   a  are provided with light sources  13  and  14  formed of a lens and a lamp and the light receiving holes  1   b  and  2   b  are provided with photodetector devices  23  and  24  of a photodiode or the like. As the light source, other than the lamp, that employing a semiconductor, such as a light-emitting diode or a laser beam, may be used.  
         [0034]    Further, at the portions close to the forefront of the measuring cylinder  12 , there are provided a light projecting hole  3   a  and a light receiving hole  3   b  opposing each other and a light source  15  is provided for the light projecting hole  3   a , while a photodetector device  25  is provided for the light receiving hole  3   b.    
         [0035]    In the above described structure, at the time of measurement, the indenter hammer  3  advances in the direction of the arrow A and, when it reaches the position of the light projecting hole  1   a , the light beam being emitted from the light source  13  and received by the photodetector device  23  through the light projecting hole  1   a  and the light receiving hole  1   b  is blocked by the indenter hammer  3 .  
         [0036]    When the indenter hammer  3  further advances in the direction of the arrow A and reaches the position of the light projecting hole  2   a , the light beam being emitted from the light source  14  and received by the photodetector device  24  through the light projecting hole  2   a  and the light receiving hole  2   b  is blocked by the indenter hammer  3 .  
         [0037]    The indenter hammer  3  further advances in the direction of the arrow A, impacts against and rebounds from the specimen  01 , and moves in the direction opposite to the arrow A. Then, first, the light beam being received by the photodetector device  24  is blocked and, then, the light beam being received by the photodetector device  23  is blocked.  
         [0038]    The time T 1  elapsed between the blocking of the light to the photodetector device  23  and the blocking of the light to the photodetector device  24  and the time T 2  elapsed between the blocking of the light to the photodetector device  24  and the blocking of the light to the photodetector device  23  can be measured by a later described electronic circuit (of FIG. 2) in accordance with ON-OFF signals from the photodetector devices  23  and  24 .  
         [0039]    Meanwhile, the distance between the light projecting hole  1   a  and the light projecting hole  2   a , i.e., the distance between the light receiving hole  1   b  and the light receiving hole  2   b , is known (to be S in the present embodiment). Hence, the impacting velocity V 1  of the indenter hammer  3  can be obtained by calculating the ratio of S to T 1  (S/T 1 ), while the rebounding velocity V 2  of the indenter hammer  3  can be obtained by calculating the ratio of S to T 2 (S/T 2 ).  
         [0040]    Now, the circuit for calculating the times T 1  and T 2  in accordance with the ON-OFF signals from the photodetector devices  23  and  24  will be described.  
         [0041]    Referring to FIG. 2, reference numeral  21  denotes a pulse counter for counting timing pulses  22   a  (clock pulses) generated in a pulse generator  22 .  
         [0042]    The pulse counter  21  is adapted such that signals from the photodetector devices  23 ,  24 , and  25  are input thereto. In the pulse counter  21 , the number N 1  of the timing pulses  22   a  from the moment the signal indicating that the light to the photodetector device  23  was blocked (an OFF signal from the photodetector device  23 ) was input to the moment the signal indicating that the light to the photodetector device  24  was blocked (an OFF signal from the photodetector device  24 ) was input and the number N 2  of the timing pulses  22   a  from the moment an OFF signal from the photodetector device  24  was input to the moment an OFF signal from the photodetector device  23  was input are respectively counted.  
         [0043]    T 1  and T 2  are calculated in an operation device  26  in accordance with the numbers of pulses N 1  and N 2  counted by the pulse counter  21  and the frequency f of the timing pulse  22   a  and, further, the impacting velocity V 1  and the rebounding velocity V 2  of the indenter hammer  3  are calculated in accordance with T 1 , T 2 , and the distance S between the light receiving holes  1   b  and  2   b.    
         [0044]    The light projecting hole  3   a  and the light receiving hole  3   b , as well as the light source  15  and the photodetector device  25 , are provided for confirming that the indenter hammer  3  has impacted the specimen (face) and rebounded therefrom. Namely, when ON-OFF signals from each of the photodetector devices have been received by the pulse counter  21  in the order of an OFF signal from the photodetector device  23 →an OFF signal from the photodetector device  24 →an OFF signal from the photodetector device  25 →an ON signal from the same, it is determined that the indenter hammer  3  properly rebounded and, thereupon, the number of pulses N 1  and N 2  are output from the pulse counter  21 .  
         [0045]    Thus, in the embodiment, since the indenter hammer velocity (detecting) sensor is provided by that of a photoelectric type, it is possible to carry out, the detection having the detecting accuracy of the velocity of the indenter hammer unaffected by the indenter hammer velocity and, further, the measurement can be carried out without being affected by environmental magnetism or magnetism in the specimen.  
         [0046]    According to the Equotip type hardness tester of the invention and the method of detecting velocitys of the indenter hammer of the hardness tester, as described above in detail, the following effects or advantages can be obtained:  
         [0047]    (1) The time required for the indenter hammer to travel the distance between the light receiving holes during its impacting course and the time required for the same to travel the distance between the light receiving holes during its rebounding course are respectively measured and, in accordance with each of the measured times and the distance between the light receiving holes, the impacting velocity and rebounding velocity of the indenter hammer against and from the specimen (face) can be calculated.  
         [0048]    (2) The aforesaid times can be calculated by using a pulse counter and by having numbers of timing pulses counted by the pulse counter.  
         [0049]    (3) Since the indenter hammer velocity (detecting) sensor is provided by that of a photoelectric type, it is made possible to carry out the detection having the detecting accuracy of the velocity of the indenter hammer unaffected by the indenter hammer velocity.  
         [0050]    (4) The measurement can be carried out unaffected by environmental magnetism or a magnetized specimen.