Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 11/642,076, filed Dec. 20, 2006, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     This invention relates generally to methods and systems for measurement of objects. More particularly, this invention relates to methods and systems for measurement of cutting tools. 
     Various types of cutting tools are known and used for machining objects, such as engine blades. Each cutting tool has associated parameters, such as primary relief angle, flute spacing, rake angle and so forth, to define a shape and a profile thereof. Typically, performance of the machined objects may depend on the parameters of the cutting tools. Accordingly, inspection of the cutting tools is required from time-to-time to ensure a desired performance of the cutting tools. In general, the parameters associated with the cutting tools are estimated and compared to desired values for determining the cutting performance of the cutting tools. 
     Different measurement methods for the cutting tools are employed to determine the parameters of such cutting tools. For example, the cutting tools are sliced and an optical comparator or a hard gage is employed to measure the parameters at any section of the sliced cutting tools. However, this technique requires physical slicing of the cutting tools, thereby making them unusable for future machining. In addition, certain methods employ image-processing techniques for estimating the tool parameters from captured projections. However, such measurement methods are limited to estimation of a minority of the tool parameters and are unable to provide measurements for all of the parameters associated with the cutting tools. Further, existing parameter measurement techniques for the cutting tools are time-consuming, relatively expensive and are less accurate than desired. 
     Therefore, there is a need for a new and improved method for extraction of parameters of cutting tools. 
     BRIEF DESCRIPTION 
     A method for measurement of a cutting tool is provided in accordance with one embodiment of the invention. The method comprises positioning the cutting tool on a moveable stage, performing a first rotary scan of a first section of the cutting tool to generate a first scanning point cloud, segmenting the first scanning point cloud, performing a second rotary scan of the first section based on the segmentation of the first scanning point cloud, and extracting the parameters of the first section based on the second rotary scan of the first section. 
     Another embodiment of the invention further provides a system for measurement of a cutting tool. The system comprises a stage configured to position the cutting tool, a range sensor configured to scan the cutting tool and a controller. The controller is configured to control the range sensor to perform a first rotary scan of a first section of the cutting tool to generate a first scanning point cloud and segment the first scanning point cloud, and further to control the range sensor to perform a second rotary scan of the first section based on the segmentation of the first scanning point cloud to extract the parameters of the first section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an example cutting tool; 
         FIG. 2  is a schematic diagram of a measurement system for measuring the cutting tool in accordance with one embodiment of the invention; 
         FIG. 3  is a schematic diagram of a range sensor of the measurement system in  FIG. 2 ; 
         FIG. 4  is a schematic diagram useful for illustrating a first scanning point cloud of an object with some points absent; 
         FIGS. 5(   a )- 5 ( b ) are schematic diagrams useful for illustrating segmentation of a first scanning point cloud of an object; 
         FIG. 6  is a schematic diagram of example scanning paths of a first scanning point cloud of an example cutting tool; and 
         FIG. 7  is a second scanning diagram of the cutting tool shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the subsequent description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. 
     In embodiments of the invention, parameters of different types of cutting tools, such as ball end mills, flat end mills, drills and reamers may be extracted. Referring to  FIG. 1 , a cutting tool  10 , such as a ball end mill is illustrated. It should be noted that the invention is not limited to any particular type of cutting tool. Rather, the example depicted in  FIG. 1  is merely illustrative. The cutting tool  10  comprises a shank  11  and a cylindrical cutting body  12 . The cutting body  12  comprises a side portion  121  and a tip  122 . In the illustrated example, the tip  122  comprises a rounded tip. For other cutting tools, the tip  122  may comprise other shapes, such as a flat tip when the cutting tool  10  comprises a flat end mill. 
     In the illustrated example, the cutting body  12  comprises multiple cutting edges and multiple flutes  13  based on a desired profile of machined parts. In one example, a two-flute mill may be employed for cutting slots or grooves. A four-flute mill may be used for a surface milling operation. The cutting tool  10  has a plurality of parameters associated with the cutting body  12 . Non-limiting examples of the parameters comprise flute spacing, an axial primary relief angle, a radial primary relief angle, a radial rake angle, concentricity, a core diameter, an axial rake angle, and a helix angle, for the illustrated example. 
       FIG. 2  is a schematic diagram of a measurement system  20  for extracting the parameters of the cutting tool  10  in accordance with one embodiment of the invention. As illustrated in  FIG. 2 , the measurement system  20  comprises a base  21 , a stage  22 , a range sensor  23 , and a controller  24 . In the illustrated embodiment, the stage  22  comprises a first stage  220  and a second stage  221 . The first stage  220  is moveably disposed on the base  21  and comprises a positioning element  222  comprising a bottom element  223  and an upper element  224  stacked together. In one embodiment, the bottom element  223  and the upper element  224  may move along an X-axis and a Y-axis relative to the base  21 , respectively. Additionally, the first stage  220  may further comprise a rotatable element  225  rotatably disposed on the upper element  224  for holding the cutting tool  10 . Accordingly, the cutting tool  10  may move along the X-Y-axis and rotate about a Z-axis relative to the base  21  with the linear movement of the positioning element  222  and rotation of the rotatable element  225 . 
     In one non-limiting example of the invention, the first stage  220  may move along the X-axis within a range of approximately zero millimeters to approximately fifty millimeters with a resolution of approximately 0.1 micrometers, and may move along the Y-axis within a range of approximately zero millimeters to approximately one hundred millimeters with a resolution of approximately 0.1 micrometers. In other embodiments, the first stage  220  may move along the X-axis and/or the Y-axis within other suitable ranges having any suitable resolution. Additionally, the rotatable element  225  may rotate approximately 360 degree with a resolution of approximately 0.0001 degrees. Alternatively, the rotatable element  225  may rotate within other suitable ranges with other suitable resolutions. 
     In the illustrated embodiment, the second stage  221  is fixedly disposed on the base  21  to moveably hold the range sensor  23  and adjacent to the first stage  220 . In one example, the range sensor  23  may move on the second stage  221  along the Z-axis. In more particular examples, the range sensor  23  may move along the Z-axis within a range of approximately zero millimeters to approximately 250 millimeters with a resolution of approximately 0.1 micrometers. In other embodiments, the range sensor  23  may move along the Z-axis within other suitable ranges and with other suitable resolutions. 
     In certain embodiments, the range sensor  23  may also move on the second stage  221  along the X-axis and Y-axis within a range and with a resolution substantially similar to these of first stage  220 . In other embodiments, the second stage  221  may be moveably disposed on the base  21 . Accordingly, in embodiments of the invention, the controller  24  may control the first stage  220  and the second stage  221  to cooperate to position the range sensor  23  at variable distances from the cutting tool  10  to measure the points on the cutting tool  10 . 
     In the illustrated embodiment, the controller  24  comprises at least one of a computer, a database, and/or a processor to control the movement of the stage  22  and the range sensor  23 , and to store and analyze the measured data points from the range sensor  23 . It should be noted that the present invention is not limited to any particular computer, database or processor for performing the processing tasks of the invention. The term “computer”, as that term is used herein, is intended to denote any machine capable of performing the calculations, or computations, necessary to perform the tasks of the invention. The term “computer” is intended to denote any machine that is capable of accepting a structured input and of processing the input in accordance with prescribed rules to produce an output. It should also be noted that the phrase “configured to” as used herein means that the computer is equipped with a combination of hardware and software for performing the tasks of the invention, as will be understood by those skilled in the art. Additionally, the measurement system  10  may further comprise a monitor  25 , such as a LCD to display data. 
       FIG. 3  illustrates a schematic diagram of an example the range sensor  23 . In the illustrated example, the range sensor  23  comprises an optical sensor  30  and a periscope  31  coupled to the optical sensor  30 . The optical sensor  30  comprises a conoscopic sensor, such as the Optimet Smart Probe described in U.S. Pat. No. 5,953,137. The periscope  31  further comprises a lens  32 . Alternatively, the optical sensor  30  may be another suitable ranging sensor. 
     In the illustrated embodiment, a light source (not shown) generates and directs a beam of light  33 , such as a laser with a wavelength of 670 nm on a point of the cutting tool  10  after the light  33  passes through the optical sensor  30  and the periscope  31  in turn. Then, a beam of reflected light  34  is generated because of diffusion of the light  33  on the point of the cutting tool  10 . The diffused light  34  passes through the periscope  31  and is detected by the optical sensor  30 . Subsequently, the controller  24  (shown in  FIG. 2 ) retrieves a distance of the point on the cutting tool  10  from the optical sensor  30  and extracts the parameters of the point by analyzing information in the detected light  34 , which is known to one skilled in the art. In one or more embodiments of the invention, with the rotation of the cutting tool  10 , the optical sensor  30  may detect diffused light from different points on the cutting tool  10  so that the controller  24  extracts the parameters of the cutting tool  10 . 
     In one embodiment, the controller  24  may determine the distance with an accuracy of approximately ±1.5 microns based on the information in the detected lights by the range sensor  23 . In other embodiments, the controller  24  may determine the distance with other suitable accuracy. In the illustrated embodiment, the incident light  33  has a frequency of up to approximately 3000 kilohertz. Alternatively, the incidence light  33  may have another suitable frequency. 
     For the arrangement illustrated in  FIG. 3 , the range sensor  23  further comprises a rotation mechanism  35  coupled to the periscope  31 . In one embodiment, the controller  24  may control the rotation mechanism  35  to rotate the periscope  31  within a range of approximately zero degree to approximately ninety degree, or other suitable ranges. Thus, in embodiments of the invention, the rotation mechanism  35  rotates the periscope  31  to enable the lens  32  to align with the points on the side portion  121  or the tip  122  (shown in  FIG. 1 ) of the cutting body  12 . In certain embodiments, the optical sensor  30  may also be rotatable. 
     As illustrated in  FIGS. 1-3 , during operation, the controller  24  controls the range sensor  23  and the first stage  220  holding the cutting tool  10  to move cooperatively so that the lens  32  first aims at a first desired section of the side portion  121  of the cutting body  12  with an appropriate distance therebetween. Then, the measurement system  20  rotates the cutting tool  10  while the light  33  scans along the first desired section with the rotation of the cutting tool  10 . Meanwhile, the range sensor  23  detects the detected light  34  diffused from the first desired section and outputs the detected information in the light  34  to the controller  24  for analyzing to generate a first scanning point cloud of the first desired section of the cutting tool  10 . In one embodiment, the controller  24  may adjust the power of the light source for subsequent scans based on the signal to noise ratio of the detected light  34 . 
     In certain applications, the complex geometry of the cutting body  12  and limited working range of the range sensor  23  may cause the first scanning point cloud to miss some points of the first desired section.  FIG. 4  shows a diagram useful for illustrating an exemplary first scanning point cloud of a section of an object (not shown) with some points absent. In other applications, the first scanning point cloud may include all points of the first desired section. 
     When missed points exist, the measurement system  20  further moves adaptively the cutting tool  10  to perform a subsequent scan to supplement the points absent based on the first scanning point cloud. In embodiments of the invention, the range sensor  23  has a focal length L, and works at a working range L±T 0 , such as L±0.8 mm to scan the different points on the side portion  121  of the cutting body  12 . 
     In one embodiment, the controller  24  may employ predictive algorithms to supplement the absent points. That is, positions of the absent points may be determined based on positions of present points on the first scanning point cloud. In one example, firstly, selecting a present point P i  proximate to an absent point P i+1 , such as an end point P i  of a gap formed by the points absent, on the first scanning point cloud with a distance from the range sensor  23  being X i . Thus, with the movement of the cutting body  12 , the distance X i  may be used for predicting a stage increment displacement (X i+1 ) between the absent point P i+1 , and the range sensor  23 . When the distance X i+1 , is in the range of L±T 0 , and is larger or less than the distance L, the measurement system  20  moves the cutting tool  10  and/or the ranger sensor  23  to adjust the distance X i+1 to be proximate to the distance L so as to retrieve the position of the absent point P i+1 . Similarly, a next absent point P i+2  may be retrieved based on the point P i+1 . Therefore, other absent points may be deduced by analogy. However, in this example, the system  20  may have to adjust the stage very frequently for every adjacent two positions have different sensor readouts, in other words, the X i+1  is always different from X i , which may cause vibration of the first stage  220 . 
     In other examples, in order to avoid the vibration of the first stage  220 , when the distance X i+1 , may be in a range of L±T 1  (T 1 &lt;T 0 ), such as L±0.2 mm, the system  20  would retrieve this point without adjusting the position of the first stage  220 . In embodiments of the invention, the points on the cutting body  12  with a distance within the working range of the range sensor  23  may be detected. However, in order to avoid adding too much inaccuracy to the first point cloud, the range of L±T 1  is selected based on experience. Additionally, when the distance X i+1  is larger than L±T 1  and less than L+T 0 , or larger than L−T 0  and less than L−T 1 , the measurement system  20  adjusts the position of the first stage  220  to enable the distance X i+1  to be in the range of L±T 1  for a scan. In one embodiment, the larger the distance X i+1  is than L+T 1 , the quicker the system  20  adjusts the first stage  220 . 
     Thus, the positions of other absent points may be supplemented. In certain embodiments, distances of some points from the range sensor  23  may be beyond the working range of the range sensor  23 , since without a compute aided design (CAD) model of the cutting tool  10  in the controller  24 , the system  20  may not identify the actual location of the points. Consequently, these points may be still absent and may be retrieved in a second scan of the first section, which will be described below. 
     Subsequently, the controller  24  analyzes and segments the first scanning point cloud.  FIGS. 5(   a )- 5 ( b ) illustrates exemplary diagrams useful for illustrating segmentation of a first scanning point cloud of an object (not shown). For the example illustrated in  FIG. 5(   a ), the controller  24  first analyzes a convex hull of the first scanning point cloud of the object to identify feature points thereon, such as edge points including the points A, B and C, and other feature points, such as the points D, E, F, G, H and I, which can be easily implemented by one skilled in the art. Then, the controller  24  calculates a distance of two adjacent feature points according to a certain order and compares the distance with a predetermined value therein. In one example, when the distance is larger than or equal to the predetermined value, the controller  24  would identify these points, such as the points A, D, B, E, C and F. Thus, a first segmentation of the first scanning point cloud is performed based on the segment of these feature points. For the example illustrated in  FIG. 5(   a ), the first scanning point cloud is segmented into six segments based on the convex hull analysis. 
     As illustrated in  FIG. 5(   b ), the controller  24  analyzes each segment in the first segmentation to perform a second segmentation. In one or more embodiments of the invention, every point in the first scanning point cloud has a normal perpendicular to a tangent of the point. Taking the point cloud in the segment AD as an example, that is, the controller  24  may analyze a normal of each point on the point cloud successively from the point A to the point D. When an angle between a normal of a point, such as the point J and the normal of the point A approximates or is equal to a predetermined angle, such as 80 degrees, the controller  24  defines the point cloud between the two points A and J as a scanning path. Similarly, the point cloud between A and D is segmented to different scanning paths. Thus, the second segmentation for the first scanning point cloud may be implemented. 
     Similar to the first and second exemplary segmentations shown in  FIGS. 4-5 , and as illustrated in  FIG. 6 , the first scanning point cloud of the cutting tool  10  can be segmented into different scanning paths, which are illustrated by lines  60  with different symbols (in this example, the first scanning point cloud is segmented into 30 scanning paths). Then, the measurement system  20  performs a second scan to scan the first desired section of the side portion  121  of the cutting body  12  according to the different scanning paths in the second segmentation shown in  FIG. 6  to retrieve a second scanning point cloud shown in  FIG. 7  with higher accuracy than the first scanning point cloud. Meanwhile, the parameters on the first desired section are extracted. 
     In one embodiment, during the second scan, an incidence direction of the light  33  may be fixed. Therefore, the controller  24  may control the first stage  220  to first rotate, and then move the cutting tool  10  linearly to enable the lens  32  to face different portions of the first desired section according to the respective scanning paths of the second segmentation for scan. In other embodiments, the range sensor  23  may also rotate to change the incidence direction of the light  33  to cooperate with the first stage  220  holding the cutting tool  10 . 
     In certain embodiments, with respect to the points absent from the first scan, during the second scan, the measurement system  20  may supplement these points by linearly scanning the gap formed by the absent points and/or by scanning the gap along extension lines of two end points of the gap. In one example, the extension lines of the two end points of the gap may be formed by connecting the two points with a central point O of the first scanning point cloud, respectively. 
     In some embodiments, the parameters of the side portion  121  of the cutting body  12  may also be extracted. In one example, firstly, the measurement system  20  controls the range sensor  23  and the first stage  220  holding the cutting tool  10  to move cooperatively so that the lens  32  faces a second desired section of the side portion  121  spaced away from the first section with a desired distance. Then, the first and second scans implemented on the first section may be used for scanning the second section to get a second scanning point cloud. Next, the measurement system  20  calculates a helix angle by analyzing the parameters of the first and second sections, and performs a side helical scanning according to the helix angle to get a side scanning point cloud of the side portion  121 . 
     In other embodiments, after performing the side scanning, the measurement system  20  may move the range sensor  23  to align with the tip  122  of the cutting tool  10 , and rotate the cutting tool  10  to scan the tip  122  to get a tip scanning point cloud. Thus, a 3D scanning point cloud (not shown) of the cutting tool  10  may be retrieved. Meanwhile, the parameters of the cutting tool  10  may be extracted and can be displayed on the monitor  25  for one to check whether the cutting tool  10  meet specifications. 
     While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the disclosure as defined by the subsequent claims.

Technology Category: 3