Patent Publication Number: US-8539844-B2

Title: Apparatus and methods for measuring a material property

Description:
FIELD OF THE INVENTION 
     The present invention relates to measurement for a material property, particularly an apparatus as well as the method thereof for measuring a material property of a matter using an elastic member. 
     BACKGROUND OF THE INVENTION 
     It would be an advanced function of a tactile sensor for being able to verify either the softness or the hardness of a matter, particularly being utilized to identify different portions of an animal&#39;s body based on the softness or hardness thereof. However, those tactile sensing apparatuses known to the art are either too complicated or short in performance. These shortages render the currently prevailed tactile sensors hard to be used for identifying physical materials as soft as tissues of human bodies. 
     Please refer to  FIG. 1 , which is a schematic diagram illustrating an endoscope  10  capable of verifying the hardness of a tissue. It can be observed from  FIG. 1  that, an external structure  12  is disposed at the front end of a traditional endoscope  11  for adapting a spring  13  with an observation window  14  and a filter  15  at the front. The axis of the endoscope  10  lies along the direction of the Z-axis.  FIG. 2  shows a cross-sectional view of the spring  13  of the endoscope  10  at a plan A-A illustrated in  FIG. 1 . Apparently, the endoscope  10  is good for used in analyzing material properties, such as hardness or elastic coefficient, of a matter or a tissue in front of the endoscope  10 , by collecting the deformation of the spring  13  due to a force Fz along the direction of Z-axis. However, according to  FIG. 2 , those external forces at either the direction of X-axis Fx and the direction of Y-axis Fy is not measurable by the endoscope  10 . Besides, the effectiveness in terms of determining the degree of hardness for the apparatus illustrated in  FIG. 1  is limited, and sometimes causes misjudging. 
     Some people suggested a method for verifying the mechanical properties of a matter by using the transmission of vibration signals. According to a research resulting with low-frequency vibrations, however, the measurement at low power may easily be disturbed by noises, and the accuracy thereof is insufficient. Some other sensing device for detecting material properties based on different physical concepts are also hard to be used for distinguishing soft materials such as sponge and gelatin. 
     According to the above-mentioned, there is a need to develop a new method for measuring a material property of a matter to overcome all those deficiencies of the prior arts. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to instantly verify the hardness or elastic coefficient of a specimen by measuring the stress difference at two portions of different mechanical property in a member, which can be produced through a simple process. 
     To achieve the abovementioned objective, the present invention provides a method for producing a measurement apparatus for measuring a material property. The method includes steps of (a) providing a pressure sensing component having a first and a second surfaces; (b) disposing a first and a second electrodes on the first surface; and (c) disposing an elastic member having a first and a second portions on the first surface, wherein the first and the second portions of the elastic material have different values of an elastic coefficient, and cover the first and the second electrodes, respectively. 
     In accordance with another aspect of the present invention, a measurement apparatus for measuring a material property of a matter is provided. The measurement apparatus comprises a pressure sensing component, a first and a second electrodes, and an elastic member. The pressure sensing component has a first and a second surfaces. The first and the second electrodes are disposed on the first surface. The elastic member has a first portion and a second portion, and is disposed on the first surface. The first and the second portions of the elastic material have different values of an elastic coefficient, and cover the first and the second electrodes respectively. 
     In accordance with a further aspect of the present invention, a method of measuring a material property of a matter is provided. The method comprises steps of: (a) providing a measurement material having a first surface and a second surface opposite to the first surface, wherein the second surface includes a first and a second portions having different measurements of a mechanical property; (b) contacting the first surface with the matter; (c) measuring a first and a second stresses due to the contact, corresponding to the first and the second portions, respectively; and (d) estimating the material property based on the first and the second stresses. 
     The above objects and advantages of the present invention will be more readily apparent to those ordinarily skilled in the art after reading the details set forth in the descriptions and drawings that follow, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing an endoscope according to the prior art; 
         FIG. 2  is a schematic diagram showing a cross-sectional view of the spring  13  of the endoscope  10  at a plan A-A illustrated in  FIG. 1 ; 
         FIGS. 3(A) and 3(B)  are schematic diagrams showing the method for measuring a material property of a body under inspection in accordance with one embodiment of the present invention; 
         FIGS. 4(A)-4(I)  are schematic diagrams showing a process of producing apparatus for measuring a material property according to a preferred embodiment of the present invention; 
         FIG. 5  is a schematic diagram showing an experiment result obtained by the method and measurement apparatus according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     In the field of Mechanics of Materials, parameters used for identifying the mechanical property of materials include elastic coefficient (Modulus of Elasticity), hardness, density and etc. For example, the Young&#39;s Modulus which indicates a relation between tensile stress and extension of a specimen is a commonly used elastic coefficient. If a body includes two portions which are obviously distinguishable in terms of a mechanical property and disposed at right and left, stresses measured from the two portions will be different when a compression is loaded to the body from top to its bottom, for the harder portion of the body bears more loading. The difference of the stresses measured from the two portions varies due to the mechanical property of the material that provides the compression. 
     Please refer to  FIG. 3(A) , which is a schematic diagram showing an apparatus and a method thereof for measuring a material property of a body under inspection in accordance with one embodiment of the present invention. According to  FIG. 3(A) , a measurement material  30  with a first surface  311  and a second surface  312  is composed of a first portion  321  and a second portion  322 , where the mechanical property of the materials (for example an elastic coefficient) of the first and the second portions  321 ,  322  are E 1  and E 2  respectively, and there is a significant difference between E 1  and E 2 . A first and a second locations  331 ,  332  are marked on the second surface  312 , and face the first and the second portions  321 ,  322  respectively, for the need of further descriptions set forth below. It can be observed from the illustration of  FIG. 3(A)  that, the second surface  321  of the measurement material  30  comprises surfaces of the first portion  321  and the second portion  322  separately. To describe in a convenient way, the first and the second portions  321 ,  322  are disposed along a horizontal direction, while the first and the second surfaces  311 ,  312  are the upper and the bottom surfaces of the measurement material  30  respectively, and the value of the elastic coefficient E 1  is larger than that of E 2 . 
     Notably, the disposition of embodiment for achieving the anticipated effects of the present invention is not limited to the above-mentioned example. Elastic coefficients indicate the degree of softness or hardness. As for the same type of material, the density thereof is also related to the elastic coefficients or hardness thereof. Therefore, the present invention is applicable for estimating material properties of a specimen based on the differences in terms of hardness or density of the two portions of the measurement material. 
     Referring to  FIG. 3(A) , a soft specimen is placed on the first surface  311  of the measurement material  30 , external forces F are applied to compress both the soft specimen and the measurement material  30  simultaneously, and deformations result in the contact due to the compression occur at the areas near the first surface  311 . According to the illustration, it can be observed that the deformation of the second portions  322  is larger than that of the first portion  321 , for the first portion  321  has a larger elastic coefficient (Young&#39;s Modulus for example) E 1  which indicates a relatively tougher material property. At this moment, one may obtain different stress values by measuring the first and second locations  331 ,  332 , based on the above-mentioned concept of Mechanics of Materials. According to one preferred embodiment of the present invention, a simple method is to dispose a pressure-sensing material (e.g. piezoelectric material, not shown) underneath the second surface  312  to collect voltage values V 1 , V 2  from locations near the first and second locations  331 ,  332  respectively. Usually the voltages produced from a piezoelectric material of a uniform thickness are positively propositional to the pressure stresses at the measurement areas. Thus, the ratio of the two stresses measured at the locations  331 ,  332  can be obtained from that of the two voltages V 1 , V 2 . 
     The right portion of  FIG. 3(A)  illustrates the values of the voltages V 1 , V 2  measured from different locations underneath the first and second portions  331 ,  332 , where the dotted line indicate the values of V 1 , the solid lines indicate the values of V 2 , and the distance between the two different locations corresponding to each pair of data is shown on the X-axis. The experimental results are in consistence with the expectation of the above-mentioned concept, which anticipates the values of V 1  shall always above the values of V 2 . 
     Please refer to  FIG. 3(B) , which illustrates the same measurement material  30  for measuring a specimen of a harder material. According to the illustrations, external forces F are applied to compress both the hard specimen and the measurement material  30  simultaneously. However, deformations result in the contact due to the compression occur at the areas near the first surface  311  are much less that those in the illustrations of  FIG. 3(A) . It can be observed that the voltage difference between V 1  and V 2  resulting from the some device allocation with that in  FIG. 3(A) , except the material property of the specimen, is significantly higher in  FIG. 3(B)  (referring to the right portion of  FIG. 3(B) ). Comparing the differences between those illustrations in  FIGS. 3(A) and 3(B) , one may obtain the ratios of V 1  to V 2  or the corresponding stress ratios, which can be used for estimating material properties relevant to the softness or hardness of the tested material, for examples, hardness or elastic coefficients. When the ratio of V 1  to V 2  is higher, it can be realized that the Young&#39;s modulus of the material of the tested matter is higher. 
     Referring again the right portions of  FIGS. 3(A) and 3(B) , it can be observed that the relation between the measured voltages V 1  and V 2  are related to the distance between the locations  331  and  332  where those measurements are implemented. When the two locations  331  and  332  are either very close or far away, the difference between V 1  and V 2  is insignificant. While the two locations  331 ,  332  are right under the middle of the first and the second portions  321 ,  322  respectively, in other words the distance thereinbetween is about the half of the maximum distance the two locations  331 ,  332  could be disposed, a maximum difference of the two voltages V 1  and V 2  is obtained. Accordingly to a preferred embodiment, the two locations  331 ,  332  for data collecting are disposed near the center areas underneath the first and second portions  321 ,  322  of the measurement material  30 , respectively. 
     Please refer to  FIGS. 4(A) to 4(I) , which schematics a process of producing apparatus for measuring a material property according to a preferred embodiment of the present invention.  FIG. 4(A)  illustrates a flexible substrate  41  plated with a conductive material  42  on top, which can be used for making electrodes. Referring to  FIGS. 4(B) to 4(D) , which illustrate the lithography and etching process accustomed to the semiconductor industry, most of the conductive material  42  is removed while a first and a second electrodes  421 ,  422  are disposed at predetermined locations. Through similar process, a third and a fourth electrodes  423  and  424  can be produced on another flexible substrate  41 . 
       FIG. 4(E)  schematics a piezoelectric film  44  which is popular in the market. The piezoelectric film  44  comprises a pressure-sensing element  441  attached with a conductive silver glue  442  on either side thereof. The pressure-sensing element  441  usually is a PVDF thin film. According to a preferred embodiment, the two layers of conductive silver glue  442  are removed by etching, so as to obtain a sensing element  441  illustrated in  FIG. 4(F) . Preferably, a sensing thin film (for example a piezoelectric thin film) without conductive silver glue is directly utilized as the sensing element  441 . 
     Referring to  FIG. 4(G) , the first electrode  421  and the second electrode  422  are separately disposed on the upper surface of the sensing element  441 , and the third electrode  423  and the fourth electrode  424  are disposed on the lower surface of the sensing element  441  at locations corresponding to that of the first and second electrodes respectively, by properly arranging the position of the flexible substrates  41 . Accordingly, the first and the third electrodes  421 ,  423  constitutes a pair of electrodes being able to transmit the voltage signal (not shown) due to pressure stress existing at the location of the sensing element  441  between the two electrodes  421  and  423  via the two flexible substrates. According to the present embodiment, those electrodes are previously disposed on the flexible substrates, and then the flexible substrates are disposed on the two sides of the sensing element  441 , so the circuits in the flexible substrates can provide a function of transmitting the voltage signals from the electrodes. In other embodiment, the users may adopt different methods for directly disposing each pairs of electrodes on both sides of the sensing element  441  to obtain the voltage signals, and collect the signal or data with other means. 
     Referring to  FIG. 4(H) , an elastic member  45  made of an elastic material such as emulsion, rubber, resin or silicone is disposed on top of the second electrode  422 . Finally, referring to  FIG. 4(I) , the whole structure illustrated in  FIG. 4(H)  is packaged with a molding material  46 , which has a mechanical property different from that of the elastic member  45 , to form a measurement device  40 . The plastic molding process accustomed to the art may be adopted for producing the package structure of the measurement device  40  with the molding material  46 , which is at a status of a glue type before the molding process and then solidified. It can be figured out by the skilled person in the art that, according to the illustration of  FIG. 4(I) , the elastic coefficient of the portion of the measurement device  40  above the first and the third electrodes  421 ,  423  must be different from that of the portion above the second and the third electrodes  422 ,  424 , since the material property of the elastic member  45  differs from that of the molding material  46 . Therefore, the measurement device  40  is applicable to be used according the above-mentioned method for estimating a material property of a matter under test. 
     Please refer to  FIG. 5 , which schematics the relation of Young&#39;s Modulus of three test samples E 1 , E 2  and E 3  versus the corresponding voltage ratios obtained by the method and measurement apparatus according to the present invention, where E 1  denotes a very soft elastic material, E 2  denotes a rubber-like material having a type number PDM184 (made by Dow-Corning Corp.) and E 3  denotes an epoxy resin. It appears that the data shown alone the horizontal axis and those along the vertical axis are positively correlated. With the aide of the use of units in  FIG. 5 , it can be observed there is a linear relation between the voltage ration and the Young&#39;s Modulus. The Young&#39;s Modulus of the three samples spread in a wide range, which indicates the method provided by the present invention is applicable at a broad scope of use. Particularly, most of the traditional methods for determining the Young&#39;s Modulus of materials are limited for measuring materials of high hardness, while the present invention is good for measuring materials with smaller Young&#39;s Modulus or relatively soft ones (such as the sample E 1  in  FIG. 5 ). 
     According to the above, the present invention provides a method being able to instantly verify the hardness or elastic coefficient of a specimen by measuring the stress difference at two portions of different mechanical property in a member, which can be produced through a simple process. 
     Embodiments 
     
         
         1. A method for producing a measurement apparatus, comprising steps of
       providing a pressure sensing component having a first and a second surfaces;   disposing a first and a second electrodes on the first surface; and   disposing an elastic member having a first and a second portions on the first surface, wherein the first and the second portions of the elastic material have different values of an elastic coefficient, and cover the first and the second electrodes, respectively.   
     
         2. The method of embodiment 1, wherein the first and the second electrodes are firstly disposed on a flexible substrate, and then disposed on the first surface through the flexible substrate. 
         3. The method of embodiment 1, further comprise a step of:
       disposing a third and a fourth electrodes on the second surface, wherein the third and the fourth electrodes are firstly disposed on a flexible substrate, and then disposed on the second surface through the flexible substrate.   
     
         4. The method of embodiment 1, wherein the first portion is disposed on the first surface before the second portion is disposed on the first surface. 
         5. The method of embodiment 1, wherein the second portion is disposed on the first surface via a molding process. 
         6. The method of embodiment 1, wherein the elastic coefficient of the elastic member includes one selected from a group consisting of a Young&#39;s modulus, a Rockwell hardness, a Brinell hardness and a Shore hardness. 
         7. The method of embodiment 1, wherein the first portion of the elastic member is harder than the second portion thereof. 
         8. The method of embodiment 1, wherein the first portion of the elastic material is softer than the second portion thereof. 
         9. A measurement apparatus, comprising:
       a pressure sensing component having a first and a second surfaces;   a first and a second electrodes disposed on the first surface; and   an elastic member having a first and a second portions, and disposed on the first surface, wherein the first and the second portions of the elastic material have different values of an elastic coefficient, and cover the first and the second electrodes respectively.   
     
         10. The measurement apparatus of embodiment 9, further comprising a flexible substrate, and the first and the second electrodes are separately and electrically coupled to the flexible substrate. 
         11. The measurement apparatus of embodiment 9, further comprising a third and a fourth electrodes disposed on the second surface, and separately and electrically coupled to a flexible substrate. 
         12. The measurement apparatus of embodiment 9, wherein the elastic coefficient of the elastic member includes one selected from a group consisting of a Young&#39;s modulus, a Rockwell hardness, a Brinell hardness and a Shore hardness. 
         13. The measurement apparatus of embodiment 9, wherein the first portion of the elastic material is harder than the second portion thereof. 
         14. The measurement apparatus of embodiment 9, wherein the first portion of the elastic material is softer than the second portion thereof. 
         15. A method of measuring a material property of a matter, comprising steps of:
       providing a measurement material having a first surface and a second surface opposite to the first surface, wherein the second surface includes a first and a second portions having different measurements of a mechanical property;   contacting the first surface with the matter;   measuring a first and a second stresses due to the contact, corresponding to the first and the second portions, respectively; and   estimating the material property based on the first and the second stresses.   
     
         16. The method of embodiment 15, wherein the material property is a physical property related to one of an elasticity and a hardness. 
         17. The method of embodiment 15, wherein the material property of the matter is estimated according to a ratio of the first to the second stresses. 
         18. The method of embodiment 15, wherein the mechanical property includes one selected from a group consisting of a Young&#39;s modulus, a Rockwell hardness, a Brinell hardness, and a Shore hardness. 
         19. The method of embodiment 15, wherein the first portion of the measurement material is harder than the second portion thereof. 
         20. The method of embodiment 15, wherein the first portion of the measurement material is softer than the second portion thereof. 
       
    
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims that are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.