Abstract:
A non-contact laser inspection system includes a probe with a thin tubular extension into which a light redirecting mechanism is incorporated to permit inspection of small diameter cylinders. The laser inspection system contains a laser that produces a beam of light that is coincident with an axis of the probe body. A reflector in the tip of the probe deflects the laser beam perpendicular to the axis of the probe. An optical system in the probe directs directly back reflected light to a detector contained in the probe body. The probe is mounted in a rotatable shaft and the axis of the probe is aligned along the axis of the rotatable shaft. The rotatable shaft rotates the probe as it is inserted into a cylindrical hole, so the laser beam can scan the inside of the cylindrical surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/248,244 filed on Oct. 2, 2009. The disclosure of the above application is incorporated herein by reference. 
     
    
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Certain of the research leading to the present invention was sponsored by the United States Government under National Science Foundation Grant IIP-0924053. The United States Government may have certain rights to the invention. 
     
    
     FIELD 
       [0003]    The present disclosure relates to non-contact laser inspection systems and more particularly to non-contact laser inspection systems for detection of surface defects on reflective cylindrical or conical parts. 
       BACKGROUND 
       [0004]    Adequate inspection of parts in a manufacturing process is desirable in order to meet part tolerances, minimize scrap and prevent defective components from being incorporated into larger subsystems. Rapid detection of defects under conditions of high volume manufacture is particularly important. If a defective part is incorporated into a larger system, the cost of disassembling the system, identifying the defect and replacing the defective part can dramatically increase production costs. Therefore, rapid detection of defects before system integration is desirable. 
         [0005]    If parts can be inspected at the speed of a production line it may be possible to use this information for process control. If it appears that parts are drifting out of tolerance, corrective action could be taken so that defective parts are not produced. Sudden onset defects in a production system could be identified before large quantities of scrap are produced. 
         [0006]    Some common surface defects on machined surfaces may occur randomly. These include pores, chips, and scratches. Poured metal castings contain entrained air bubbles around which liquid metal can solidify. When the castings are machined these bubbles can be cut open and exposed as pores. Chips may form when pieces of metal chip off from a casting as a tool enters or exits a hole in a part. Scratches on a surface may also make a component defective. These types of defects can be difficult to detect when they occur inside cylindrical holes in a part. 
         [0007]    Complex parts, such as valve ports of automatic transmissions, may contain cylindrical holes that may vary progressively in diameter in discrete steps along the length of the cylinder. The cylinders may also be intersected by multiple slots. Valve ports may vary between about 8 to 24 millimeters in diameter and may have lengths over 100 millimeters. Defects in valve ports over areas as small as 0.1 mm 2  may cause problems or failure when used in automobile transmissions. Defects in such complex parts can be particularly difficult to detect rapidly with existing probes and sensors. 
         [0008]    Non-contact gauges of various types are used to measure dimension and surface defects using optical, capacitive, eddy current and Hall-effect sensors. Most of these gauges do not measure surface finish. Imaging systems may measure geometry and surface finish, but they typically require image analysis software which may be quite slow. In addition, some geometries do not lend themselves easily to insertion of existing gauges. 
         [0009]    Contact gauges are also used to measure dimensional accuracy and surface roughness. These gauges include coordinate measuring machines of various types and stylus gauges. Stylus gauges measure surface roughness by tracing a thin line with a diamond-tipped needle. The thin line is an extremely small fraction of the total surface area. The measurement is slow and may miss defective regions. If there are gaps in the surface, the stylus tip must be raised to avoid these gaps and avoid damage to the tip of the needle. Such characteristics make stylus gauges impractical for total part inspection on a production line. 
         [0010]    A number of optical instruments used to detect surface flaws on reflective surfaces illuminate the surface with a directed source of illumination and place a detector in a location that will not detect specularly reflected light. Instead, the detector is generally placed to detect light scattered by a defect. If there is no defect, no signal will be received by the detector, but if there is a defect that scatters light, a signal will be received by the detector. Examples of scattered light detectors are given in U.S. Pat. Nos. 6,097,482 and 7,372,557. 
         [0011]    Scattered light detection may be adequate when it is possible to position the light source and detector at different viewing angles that prevent reflected light from reaching the detector. However, for small diameter cylindrical holes this may not be practical or possible. 
         [0012]    Another approach to surface defect detection uses a diffuse beam of light to illuminate a surface and a camera or other imaging system to image the surface. The data must then be analyzed using image analysis software. Examples of this type of inspection system are given in U.S. Pat. Nos. 7,394,530, 6,516,083, 6,169,600, 5,588,068, 5,353,357, and 4,732,474. In general, the illumination system and detection path are not coincident and this approach is therefore not suitable for inspecting small diameter cylinders with lengths significantly longer than the cylinder diameter. 
         [0013]    Another technique that can inspect the inside of relatively small diameter cylinders is a confocal microscope, such as one that is commercially available from the Micro-Epsilon Corporation. This system can scan the inside of a cylinder with a focused beam of light. However, the focal spot on the surface of the cylinder is so small that a considerable time is required to scan the total area of a cylinder. 
         [0014]    Accordingly, there is a need in the art for an improved non-contact laser inspection system capable of rapidly detecting surface defects and inspecting small diameter bores. 
       SUMMARY 
       [0015]    This disclosure relates to an instrument and method for the rapid inspection of reflective surfaces of cylindrical parts for surface finish defects in a high volume production environment. A non-contact laser system uses an optical configuration in which a laser beam is directed substantially perpendicular to the surface to be inspected. Some of the laser beam light is back reflected along the trajectory of the incident beam. This makes it possible to use the detector to detect surface defects in small diameter cylindrical holes including cylinders in which the hole depth is much larger than the hole diameter. Using this system a reflective surface with no defects will produce a large optical return signal. Conversely, surface defects that scatter the incident beam will result in a dip in the return light intensity. 
         [0016]    One embodiment of the present disclosure includes a laser probe with a thin tubular extension or tip into which a light redirecting mechanism is incorporated to permit inspection of small diameter cylinders. The probe contains a laser that produces a beam of light that is coincident with an axis of the tubular extension. A reflector in the tubular extension of the probe deflects the laser beam substantially perpendicular to the surface of the cylindrical or conical part being inspected. An optical system in the probe directs directly-back-reflected and directly back scattered light to a detector contained in the probe body. The probe body also contains electronics to amplify the detector signal. A slip ring mounted on the probe shaft permits electric power to be input to the probe and data to be retrieved while the probe is spinning. The probe is mounted on a rotatable shaft and the axis of the probe is aligned along an axis of the rotatable shaft. The rotatable shaft rotates the probe as it is inserted into a cylindrical or conical hole, so the laser beam can scan the inside of the cylindrical or conical surface. Linear and rotary encoders monitor the probe axial and angular positions. Data from the probe and from the encoders are collected using a data acquisition system and the data is analyzed and displayed using a computer and analysis and display software. 
         [0017]    In another aspect of the present disclosure, an inspection probe for inspecting reflective cylindrical or conical surfaces of manufactured components is provided. The probe includes a laser system, an optical system, an optical detector, and a computer. The optical system directs a laser beam perpendicular to the surface being inspected and directs back-reflected light to an optical detector. The optical detector detects the back-reflected laser light from the surface. 
         [0018]    In yet another aspect of the present disclosure, the computer includes software that compares the detected light signal to a light signature from a known cylindrical or conical surface or cylindrical or conical surface with known defects and determines a condition of the surface. 
         [0019]    In yet another aspect of the present disclosure, the probe further includes a filter in front of the detector to reduce unwanted light. 
         [0020]    In yet another aspect of the present disclosure, the reflective cylindrical surface is one of a valve port of a valve body or pump cover of an automatic transmission, a brake cylinder, a cylindrical reflective surface of a component of a shock absorber, the surface of a hydraulic or pneumatic cylinder, the inside surface of a gas flow valve, the inside or outside surface of a reflective cylindrical manufactured part, or a component with a tapped interior thread. 
         [0021]    In yet another aspect of the present disclosure, the laser system, the optical system, and the detector are mounted inside a support structure. 
         [0022]    In yet another aspect of the present disclosure, the support structure is mounted on a support shaft. 
         [0023]    In yet another aspect of the present disclosure, the support shaft is mounted in the spindle of a machine. 
         [0024]    In yet another aspect of the present disclosure, the laser beam is aligned along an axis of the spindle. 
         [0025]    In yet another aspect of the present disclosure, the optical system includes an optional beam reducer to reduce the diameter of the parallel laser beam emitted along an axis of the spindle. 
         [0026]    In yet another aspect of the present disclosure, the laser beam is reflected by an optical reflector in a direction perpendicular to the cylindrical surface to be measured. 
         [0027]    In yet another aspect of the present disclosure, the optical system directs the return beam from the cylindrical surface onto a detector. 
         [0028]    In yet another aspect of the present disclosure, the optical system includes a polarizing beam splitter, a quarter wave plate, an optional spacer and a 90° reflector, such as a right angle prism. 
         [0029]    In yet another aspect of the present disclosure, the polarizing beam splitter, the quarter wave plate, the optional spacer, and the 90° reflector are attached together to form a single rigid component. 
         [0030]    In yet another aspect of the present disclosure, the optical detector is a photodiode. 
         [0031]    In yet another aspect of the present disclosure, the probe includes a device transmitting power to the laser and electronics in the detector and transmitting data to a computer. 
         [0032]    In yet another aspect of the present disclosure, the power and data transmitting device is mounted on the support shaft. 
         [0033]    In yet another aspect of the present disclosure, the power and data transmitting device is a slip ring. 
         [0034]    In yet another aspect of the present disclosure, the probe includes a detector electronics device mounted in the support structure. 
         [0035]    In yet another aspect of the present disclosure, the detector electronics device includes signal amplification. 
         [0036]    In yet another aspect of the present disclosure, the shaft is rotatably supported on a chuck or tool holder. 
         [0037]    In yet another aspect of the present disclosure, the chuck or tool holder is supported on a spindle. 
         [0038]    In yet another aspect of the present disclosure, the spindle is supported in a computer numerically controlled (CNC) machine or robot. 
         [0039]    In yet another aspect of the present disclosure, the CNC machine or robot is programmed to rotate and insert the probe into a reflective cylindrical component of a manufactured part. 
         [0040]    In yet another aspect of the present disclosure, the laser beam scans the surface of the cylindrical part. 
         [0041]    In yet another aspect of the present disclosure, the CNC machine or robot has axial and rotary encoders to determine axial position and rotation angle of the probe in the cylinder. 
         [0042]    In yet another aspect of the present disclosure, the data acquisition system of the computer records the angular position of data points measured by the probe. 
         [0043]    In yet another aspect of the present disclosure, data from the linear encoder is recorded by the data acquisition system. 
         [0044]    In yet another aspect of the present disclosure, a method for inspecting a machined surface is provided. The method includes the steps of: directing a laser beam perpendicularly to the machined surface, detecting a back-reflected laser beam from the machined surface, determining a signature of the detected laser beam light, and determining a condition of the machined surface from the signature. 
         [0045]    In yet another aspect of the present disclosure, the machined surface is a cylinder. 
         [0046]    In yet another aspect of the present disclosure, determining a signature includes comparing a light signature from a known surface or surface with known defects to the light signature from the inner surface of the cylinder. 
         [0047]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0048]      FIG. 1  is a schematic drawing of an inspection system in an operating environment in accordance with the principles of the present disclosure; 
           [0049]      FIG. 2  is a cross sectional view of an exemplary laser probe in accordance with the principles of the present disclosure; 
           [0050]      FIG. 3  is a cross sectional view of an exemplary laser probe in accordance with the principles of the present disclosure; 
           [0051]      FIG. 4  is a flow chart of a method for inspecting a bore according to the principles of the present disclosure; and 
           [0052]      FIG. 5  is a schematic drawing of an inspection system in an operating environment in accordance with the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It is to be understood that standard components or features that are within the purview of an artisan of ordinary skill and do not contribute to the understanding of the various embodiments of the invention are omitted from the drawings to enhance clarity. In addition it will be appreciated that the characterization of various components and orientations described herein as being “vertical” or “horizontal”, “right” or “left”, “side”, “top” or “bottom” are relative characterizations only based upon the particular position or orientation of a given component for a particular application. 
         [0054]    With reference to  FIG. 1 , a schematic diagram of inspection system  5  for inspecting workpiece  7  is shown. Inspection system  5  includes a probe  10 , probe shaft  14 , slip ring  16 , rotatable shaft  18 , positioning machine  20 , rotary encoder  22 , linear encoder  24 , data acquisition unit  26 , computer  28 , and monitor  30 . 
         [0055]    Workpiece  7  includes an at least partially reflective inner surface  9  that defines at least one bore  12 . In the example provided, bore  12  is a valve port and workpiece  7  is a valve body or pump cover in a transmission of an automobile. 
         [0056]    However, it should be appreciated that cylindrical bore  12  could exist in many other types of workpieces  7 , such as, but not limited to, brake cylinders, shock absorbers, hydraulic or pneumatic cylinders, gas flow valves, tapped internally threaded cylinders or other cylindrical manufactured parts. 
         [0057]    In the example provided, inner surface  9  includes surface defect  13 . However, it should be appreciated that surface defect  13  may not be present in a given bore  12 , or many surface defects  13  may be present in a given bore  12 . In addition, bore  12  may have other diameters, depths, types of defects  13 , and numbers of defects  13  without departing from the scope of the present disclosure. 
         [0058]    Probe  10  is disposed in bore  12 . Probe  10  is generally a laser probe, as will be described below. Probe  10  is attached to and centered on probe shaft  14 . 
         [0059]    In the example provided, slip ring  16  is mounted on probe shaft  14  and is electrically connected to the components of probe  10 , as will be described in detail below. 
         [0060]    Probe shaft  14  is mounted to rotatable shaft  18  of positioning machine  20 . Positioning machine  20  rotates and axially moves rotatable shaft  18 . Rotatable shaft  18  may be a solid bar or a hollow tube. In the example provided, positioning machine  20  is a computer numerically controlled (CNC) machine, and probe shaft  14  is mounted in a chuck (not shown) of rotatable shaft  18 . However, it should be appreciated that other positioning machines  20  capable of rotating probe  10  may be used without departing from the scope of the present disclosure. Standard machining techniques may be used to align the center of probe  10  with the axis of rotatable shaft  18 . The positioning machine  20  includes rotary encoder  22  and linear encoder  24  that indicate the angular orientation and the axial position of rotatable shaft  18  in the machining system. Rotatable shaft  18  and a portion of positioning machine  20  are commonly known in industry as a spindle. 
         [0061]    Data acquisition unit  26  may be an internal data acquisition card installed in computer  28  or an external data collection unit in communication with computer  28 . However, other types of devices that perform the same functions as computer  28  may be employed without departing from the scope of the present invention. Data acquisition unit  26  is in communication with rotary encoder  22  and linear encoder  24 . In an alternative embodiment where bore  12  may be scanned without linear position data, data acquisition unit  26  is not in communication with linear encoder  24 . 
         [0062]    Turning to  FIG. 2 , further details of probe  10  are shown. Probe  10  has body portion  104  and tip portion  106  extending from body portion  104  and partially disposed within bore  12 . Body portion  104  and tip portion  106  are preferably cylindrically shaped for improved balance during rotation. The interior of body portion  104  is preferably shaped for easy insertion and removal of optic and electronic components and may be covered by a removable outer envelope (not shown) to access the interior of body portion  104 . In the example provided, tip portion  106  is a thin walled-tube about 100 millimeters in length with an outer diameter of about 3.9 millimeters. However, other shapes, diameters and lengths may be employed without departing from the scope of the present disclosure. Body portion  104  and tip portion  106  are centered along a common axis  108 . Laser  110  is mounted in body portion  104  and is aligned to emit laser beam  112  through tip portion  106  along axis  108 . Preferably, laser beam  112  has a diameter of about 1 mm. In the example provided, an optional aperture or other type of beam reducer  117  can reduce the diameter of laser beam  112  to less than 1 mm before laser beam  112  enters tip portion  106 . Laser beam  112  may return substantially along axis  108  towards laser  110  as return beam  113 . Laser beam  112  has a predetermined polarization that interacts with other components in desirable ways, as will be described below. Proper polarization of laser beam  112  may be achieved by rotational alignment of laser  110 . In the example provided, laser  110  is a diode laser that fits loosely into a cylindrical cavity in probe body  104  and can be aligned using six set screws (not shown) to both center laser  110  in probe body  104  and align laser beam  112  along probe axis  108 . Apertures and interior surfaces that may scatter light into detector  132  are made of black material or are coated black to absorb the scattered light. Tapped threads may also be added to some interior cylindrical surfaces of probe body  104  to enhance absorption of scattered light. 
         [0063]    Polarizing beam splitter  114  is disposed on axis  108  between laser  110  and tip portion  106 . Laser  110  is oriented so that the polarization of laser beam  112  allows laser beam  112  to pass through polarizing beam splitter  114  substantially undeflected. Polarizing beam splitter  114  deflects return beam  113  due to the polarization of return beam  113 , as will be described below. Polarizing beam splitter  114  preferably deflects return beam  113  perpendicular to axis  108 . 
         [0064]    Quarter wave plate  116  is also disposed on axis  108  between polarizing beam splitter  114  and tip portion  106 . Quarter wave plate  116  is oriented to convert the polarization of laser beam  112  from linear polarization to circular polarization. Quarter wave plate  116  also converts the polarization of return beam  113  from circular polarization to linear polarization, but in a direction that is perpendicular to the original linear polarization of laser beam  112 . Beam reducer  117  is disposed between quarter wave plate  116  and tip portion  106 . 
         [0065]    Mirror  118  is disposed in and rotates with tip portion  106  on axis  108 . Preferably, mirror  118  is disposed near an end of tip portion  106  farthest from body portion  104 . Mirror  118  may be a separate reflector attached to probe tip  106 , and may be a cut and polished glass rod with a diameter of about 2 to 3 mm. However, other types, shapes and diameters of mirror  118  may be used without departing from the scope of the present disclosure. Mirror  118  is angled to deflect laser beam  112  perpendicular to inner surface  9  of workpiece  7 . In the example provided, mirror  118  is generally angled at 45 degrees with respect to axis  108 . 
         [0066]    In an alternative embodiment, mirror  118  is at a different angle with respect to axis  108  in order to inspect conical surfaces, such as the sealing surface of a valve seat of an engine head. The deflection angle of mirror  118  is preferably chosen to deflect laser beam  112  perpendicular to the specified conical surface. If the surface has been machined at the specified angle, the back reflected light will produce a large signal at the detector. If the conical angle of the valve seat is incorrect or the valve seat is misaligned or defective there will be a lower detector signal. 
         [0067]    In an alternative embodiment of a probe, a fiber optic cable (not shown) is disposed in a probe to transmit beams  112  and  113 . A laser insertion assembly (not shown) is disposed at an end of the fiber optic cable to insert laser beam  112  into the fiber optic cable. A light collimating assembly is disposed at a second end of the fiber optic cable to collimate the light from laser beam  112  exiting the fiber optic cable. Mirror  118  at the end of tip portion  106  may be used to deflect laser beam  112  perpendicular to surface  9  of bore  12 . However, other types of deflection assemblies may be used at the end of tip portion  106  to deflect laser beam  112  perpendicular to surface  9  of bore  12 . 
         [0068]    In the example provided, optional glass spacer  124  is disposed adjacent polarizing beam splitter  114  in the path of return beam  113 . Alternatively, an opaque spacer with a centered clear aperture could be used in place of the glass spacer  124 . 
         [0069]    Right angle prism  126  is disposed adjacent to glass spacer  124  and in the path of return beam  113  after return beam  113  has been deflected by polarizing beam splitter  114 . Right angle prism  126  is oriented to deflect return beam  113  in a direction substantially parallel to axis  108 . 
         [0070]    In the example provided, wavelength filter  128  and neutral density filter  130  are disposed adjacent right angle prism  126 . However, in an alternative embodiment, neutral density filter  130  may be omitted, and wavelength filter  128  may be omitted when the only potential source of light reaching detector  132  is generated by laser  110 . 
         [0071]    In the example provided, polarizing beam splitter  114 , quarter wave plate  116 , glass spacer  124 , and right angle prism  126  are held rigid by an index matching epoxy. However, the components may be held rigid in other ways without departing from the scope of the present disclosure. Preferably, any optical surface in contact with air is coated to reduce reflection. 
         [0072]    Detector  132  is disposed adjacent neutral density filter  130  in the path of return beam  113 . Detector  132  is generally a photodiode that converts optical signals to electrical signals. However, other types of detectors  132  may be used without departing from the scope of the present disclosure. 
         [0073]    Electrical cable  134  connects detector  132  with electronic circuit  136 . In the example provided, electronic circuit  136  is held in place by a lip at the bottom of a cavity  135  and thin collar  137  within probe body  104 . However, electronic circuit  136  may be placed in other locations and fixed within probe body  104  in other ways without departing from the scope of the present disclosure. 
         [0074]    Probe body  104  is attached to probe shaft  14  by screws (not shown). Probe shaft  14  has a hole (not shown) through its center and a hole perpendicular to axis  108  proximate slip ring  16 . The hole through the center can enable clean low pressure compressed air to flow through the probe body and tip to create a positive pressure shielding the optical and other internal components from the outside environment. Wiring from laser  110  and wires from circuit board  136  pass through the hole perpendicular to axis  108  in probe shaft  14  and are connected to slip ring  16 . A cable (not shown) from slip ring  16  is connected to data acquisition unit  26  in computer  28 . Power cables (not shown) connect to a power supply (not shown), providing power to probe  10 . 
         [0075]    With combined reference to  FIGS. 1 and 2 , the operation of inspection system  5  will now be described. During operation, positioning machine  20  will spin probe  10  as probe  10  enters bore  12 . For a smooth cylindrical inner surface  9 , much of laser beam  112  will be reflected directly back on itself as return beam  113 . If a surface defect  13  is present, at least some of laser beam  112  will scatter and not be reflected as return beam  113 . Thus, the intensity of return beam  113  may be used to indicate the presence of surface defect  13 . 
         [0076]    Laser beam  112  is emitted by laser  110  through polarizing beam splitter  114 , quarter wave plate  116  and beam reducer  117 , and is redirected towards inner surface  9  of workpiece  7  by mirror  118 . Upon reaching inner surface  9 , part of laser beam  112  is back reflected along the path of incident laser beam  112 . If surface defect  13  is present, at least part of laser beam  112  will not be reflected as return beam  113 . When at least part of laser beam  112  does not reflect back, any return beam  113  that does return will have lower intensity than when there is no surface defect  13 . Return beam  113  is reflected by mirror  118  through beam reducer  117  (which now may act as a beam expander) towards quarter wave plate  116 . Quarter wave plate  116  converts return beam  113  polarization so that polarizing beam splitter  114  redirects return beam  113  through spacer  124  to right angle prism  126 . Right angle prism  126  directs return beam  113  through wavelength filter  128  and neutral density filter  130  to detector  132 . When employed, neutral density filter  130  reduces return beam  113  intensity to prevent saturation of the electronic circuit  136  or data acquisition unit  26 , and wavelength filter  128  reduces the intensity of a portion of the return light corresponding to certain wavelengths. Detector  132  converts the intensity of return beam  113  into an electrical signal and sends the electrical signal through electrical cable  134  to electronic circuit  136 . Electronic circuit  136  sends a signal indicative of the intensity of return beam  113  through slip ring  16 . 
         [0077]    Data from probe  10  is transmitted through slip ring  16  to data acquisition unit  26  in computer  28 . Data from rotary encoder  22  is also sent to data acquisition unit  26 . When a pulse is received from rotary encoder  22 , data acquisition unit  26  samples the value of the signal from probe  10 . Data from linear encoder  24  may also be sent to data acquisition unit  26  to indicate the axial location at which data from probe  10  is being sampled. 
         [0078]    Computer  28  preferably analyzes the data from probe  10 , rotary encoder  22 , and linear encoder  24 . Preferably, software in computer  28  may create a three dimensional graph of probe  10  data as a function of position, representing surface  9  of bore  12 . The results of the analysis may be displayed on monitor  30 . The graph displayed on monitor  30  is provided to assist human visualization of surface  9  of bore  12 . The software in computer  28  obtains the information used to generate the graph and analyze the data from a data file created from data transmitted to computer  28  by data acquisition unit  26 . Alternatively, the software in computer  28  analyzes the data from data acquisition unit  26  and provides information about whether a part is acceptable or defective without generating a graph. 
         [0079]    In an alternative embodiment, a probe is configured to inspect the outside surface of cylinders, cones, or gears by rotating the part (not shown) rather than the probe. In this embodiment, the probe does not rotate and slip ring  16  is not included because it is not needed to transmit power to and collect data from the probe. Deflecting mirror  118  may be omitted and laser beam  112  can be directed along axis  108  directly to the part being inspected. A machine (not shown) rotates the part, and has a means of determining the axial position of the probe and rotational position of the part and transmitting this information to data acquisition unit  26  collecting data from the probe. In addition to rotating the part being inspected, the machine also moves the probe linearly relative to the rotating part or moves the rotating part linearly relative to the probe in order to scan the surface of the rotating part. 
         [0080]    The diameter of bore  12  may be determined by measuring the average intensity of return beam  113 . Smaller diameter bores  12  may have lower average return beam intensities because part of the edges of laser beam  112  may be reflected away from probe  10  due to the small radius of curvature of bore  12 . 
         [0081]    The data obtained from probe  10  may be compared with data from a master bore known to be free of defects. The workpiece  7  can be removed for further inspection if the data between the master bore and the bore  12  of the workpiece  7  deviate from each other by a predetermined amount. 
         [0082]    In an alternative embodiment of a probe, slip ring  16  is mounted on a second shaft (not shown). The second shaft is co-axial with and mounted to rotatable shaft  18  and is disposed on the side of rotatable shaft  18  opposite probe shaft  14 . A cable (not shown) is disposed in a bore (not shown) of rotatable shaft  18  to connect slip ring  16  with the probe. Mounting slip ring  16  on the second shaft improves the load balance on rotatable shaft  18  when the probe is mounted horizontally. Rotary encoder  22  can also be connected to the second shaft. It should be appreciated that the hole perpendicular to axis  108  in shaft  14  of the probe may be omitted. In the example provided, there is a hole on the second shaft perpendicular to axis  108 . 
         [0083]    In an alternative embodiment of a probe, slip ring  16  is omitted and data is transmitted wirelessly from the probe to data acquisition unit  26 . An example of wireless data transmission adapted for use in the probe is given in a paper by C. Suprock, et al. titled “A Low Cost Wireless Tool Tip Vibration Sensor for Milling” in the Proceedings of the International Manufacturing Science and Engineering Conference (MSEC2008). 
         [0084]    The data from probe  10  may also be used to determine whether axis  108  of probe  10  and an axis defined by bore  12  are coincident. If probe  10  is off center relative to the bore axis, the signal from probe  10  may be modulated with the period of the probe rotation. This modulation may be filtered out when the data is analyzed. The data may also be used as a diagnostic to monitor the relative alignment of probe  10  within bore  12 . 
         [0085]    Another alternative embodiment that does not include a slip ring is shown in  FIG. 3 , which shows a schematic diagram of inspection system  200  for inspecting workpiece  7 . Inspection system  200  includes probe  210 , base  202 , probe cover and body portion  204 , probe tip  206 , rotatable shaft  218 , rotation machine  220 , linear movement machine  223 , rotary encoder  222 , and linear encoder  224 . Rotatable shaft  218 , rotation machine  220  and rotary encoder  222  may be combined into a spindle with integral rotary encoder. Probe  210  is generally a laser probe, as will be described below. Base  202  is designed to properly position the optical and electronic components and slide along rail  226  of linear movement machine  223 . 
         [0086]    Body portion  204  does not rotate and is rigidly mounted on and moves linearly with base  202 . The interior of body portion  204  is preferably shaped for easy insertion and removal of optic and electronic components. In the example provided, body portion  204  includes a removable outer envelope that allows access to the optic and electronic components when removed. The outer envelope of body portion  204  prevents stray light from reaching the optical components, protects the probe components from the outside environment and permits low pressure compressed air to flow through probe  210 . 
         [0087]    Probe tip  206  may be attached to rotary shaft  218  with a chuck, tool holder, or collet (not shown). Probe tip  206  is rigidly held in rotatable shaft  218 , is rotatable with rotatable shaft  218  and is disposed in bore  12 . Probe tip  206  is centered on axis  308 . Probe tip  206  is preferably cylindrically shaped for improved balance during rotation. In the example provided, tip portion  206  is a thin walled-tube about 100 millimeters in length with an outer diameter of about 3.9 millimeters. However, other shapes, diameters and lengths may be employed without departing from the scope of the present disclosure. 
         [0088]    Rotatable shaft  218  is centered on axis  308  and is rotatable by rotation machine  220 . Rotatable shaft  218  includes a clear through aperture  219  through an axial dimension of rotatable shaft  218  aligned with axis  308 . Rotation machine  220  is rigidly mounted on base  202 , does not rotate, and moves with base  202  along an axis of linear machine  223 . Rotation machine  220  includes aperture  221  that surrounds rotatable shaft  218  and extends through rotation machine  220  substantially along axis  308 . Rotatable shaft  218  and rotation machine  220  may be integrated into a spindle, and rotatable shaft  218  may be disposed within aperture  221 . Rotation machine  220  includes rotary encoder  222  that indicates the angular orientation of rotatable shaft  218  in inspection system  200 . In the example provided, rotary encoder  222  is aligned with rotatable shaft  218 , and includes aperture  225  that extends through rotary encoder  222  substantially along axis  308 . However, rotary encoder  222  may be placed in other locations in which case aperture  225  may be omitted without departing from the scope of the present disclosure. 
         [0089]    Linear movement machine  223  includes linear encoder  224  and guide rail  226 . Guide rail  226  constrains movement of base  202  to linear movement along the length of guide rail  226 . Linear encoder  224  indicates the linear location of base  202  and probe tip  206  in inspection system  200 . In the example provided, linear movement machine  223  is a CNC machine. However, other machines may be used without departing from the scope of the present disclosure. 
         [0090]    Laser  310  is mounted in body portion  204  and is aligned to emit laser beam  312  through tip portion  206  along axis  308 . Preferably, laser beam  312  has a diameter of about 1 mm. In the example provided, an aperture or other type of beam reducer  317  reduces the diameter of laser beam  312  before laser beam  312  enters tip portion  206 . In an alternative embodiment, beam reducer  317  is omitted. Laser beam  312  may return substantially along axis  308  towards laser  310  as return beam  313 . Laser beam  312  has a predetermined polarization that interacts with other components in desirable ways, as will be described below. 
         [0091]    Polarizing beam splitter  314  is disposed on axis  308  between laser  310  and tip portion  206 . Laser  310  is oriented so that the polarization of laser beam  312  allows laser beam  312  to pass through polarizing beam splitter  314  substantially undeflected. Polarizing beam splitter  314  deflects return beam  313  due to the polarization of return beam  313 , as will be described below. Polarizing beam splitter  314  preferably deflects return beam  313  perpendicular to axis  308 . 
         [0092]    Quarter wave plate  316  is also disposed on axis  308  between polarizing beam splitter  314  and tip portion  206 . Quarter wave plate  316  is oriented to convert the polarization of laser beam  312  from linear polarization to circular polarization. Quarter wave plate  316  also converts the polarization of return beam  313  from circular polarization to linear polarization, but in a direction that is perpendicular to the original linear polarization of laser beam  312 . Beam reducer  317  is disposed between quarter wave plate  316  and tip portion  206 . Beam reducer  317  may act as a beam expander for beam  313 . 
         [0093]    Mirror  318  is disposed in and rotates with tip portion  206  on axis  308 . Preferably, mirror  318  is disposed near an end of tip portion  206  farthest from body portion  204 . Mirror  318  may be a separate reflector attached to probe tip  206 , and may be a cut and polished glass rod with a diameter of about 2 to 3 mm. However, other types, shapes and diameters of mirror  318  may be used without departing from the scope of the present disclosure. Mirror  318  is angled to deflect laser beam  312  perpendicular to inner surface  9  of workpiece  7 . In the example provided, mirror  318  is generally angled at 45 degrees with respect to axis  108 . However, it should be appreciated that mirror  318  may have other angles with respect to axis  308 , such as when inspection of a conical surface is desired, without departing from the scope of the present disclosure. 
         [0094]    Glass spacer  324  is disposed adjacent polarizing beam splitter  314  in the path of return beam  313 . However, in an alternative embodiment, glass spacer  324  is omitted. In another alternative embodiment, glass spacer  324  may be replaced with an opaque spacer with an aperture at its center to permit the return beam to pass through to detector  332 . Right angle prism  326  is disposed adjacent to glass spacer  324  and in the path of return beam  313  after return beam  313  has been deflected by polarizing beam splitter  314 . Right angle prism  326  is oriented to deflect return beam  313  in a direction substantially parallel to axis  308 . In an alternative embodiment, glass spacer  324  and right angle prism  326  are omitted. Such an alternative embodiment may be desirable because the spatial constraints on the location of the optical components are more relaxed than are the spatial constraints in an embodiment with a rotating probe body. 
         [0095]    In the example provided, wavelength filter  328  and neutral density filter  330  are disposed adjacent right angle prism  326 . However, in an alternative embodiment, neutral density filter  330  is omitted, and wavelength filter  328  is omitted when the only potential source of light reaching detector  332  is generated by laser  310 . 
         [0096]    In the example provided, polarizing beam splitter  314 , quarter wave plate  316 , glass spacer  324 , and right angle prism  326  are held rigid by an index matching epoxy. However, the components may be held rigid in other ways without departing from the scope of the present disclosure. Preferably, any optical surface in contact with air is coated to reduce reflection. 
         [0097]    Detector  332  is disposed adjacent neutral density filter  330  in the path of return beam  313 . It should be appreciated that detector  332  is disposed in the alternative path of return beam  313  when right angle prism  326  and glass spacer  324  are omitted. Detector  332  is generally a photodiode that converts optical signals to electrical signals. However, other types of detectors  332  may be used without departing from the scope of the present disclosure. 
         [0098]    Electrical cable  334  connects detector  332  with electronic circuit  336  and cable  338  transmits data from electronic circuit  336  to computer  28 . 
         [0099]    With continued reference to  FIG. 3 , the operation of inspection system  200  will now be described. During operation, rotation machine  220  will spin rotatable shaft  218  which spins probe tip  206  as linear movement machine  223  linearly moves base  202  so that probe tip  206  enters bore  12 . For a smooth cylindrical inner surface  9 , much of laser beam  312  will be reflected directly back on itself as return beam  313 . If a surface defect  13  is present, at least some of laser beam  312  will scatter and not be reflected as return beam  313 . Thus, the intensity of return beam  313  as a function of position of the laser spot on surface  9  may be used to indicate the presence of surface defect  13 . 
         [0100]    Laser beam  312  is emitted by laser  310  through polarizing beam splitter  314 , quarter wave plate  316 , beam reducer  317 , aperture  225  in rotary encoder  222 , aperture  219  in rotatable shaft  218 , and probe tip  206  and is redirected towards inner surface  9  of workpiece  7  by mirror  318 . Upon reaching inner surface  9 , part of laser beam  312  is back reflected along the path of incident laser beam  312 . If surface defect  13  is present, at least part of laser beam  312  will not be reflected as return beam  313 . When at least part of laser beam  312  does not reflect back, any return beam  313  that does return will have lower intensity than when there is no surface defect  13 . Return beam  313  is reflected by mirror  318  through probe tip  206 , aperture  219  in rotatable shaft  218 , aperture  225  in rotary encoder  222 , and beam reducer  317  (which now may act as a beam expander) towards quarter wave plate  316 . Quarter wave plate  316  converts return beam  313  polarization so that polarizing beam splitter  314  redirects return beam  313  through spacer  324  to right angle prism  326 . Right angle prism  326  directs return beam  313  through wavelength filter  328  and neutral density filter  330  to detector  332 . When employed, neutral density filter  330  reduces return beam  313  intensity to prevent saturation of the electronic circuit  336  or data acquisition unit  26 , and wavelength filter  328  reduces the intensity of the return light corresponding to certain wavelengths. Detector  332  converts the intensity of return beam  313  into an electrical signal and sends the electrical signal through electrical cable  334  to electronic circuit  336 . Electronic circuit  336  sends a signal indicative of the intensity of return beam  313  through cable  338 . 
         [0101]    Data from probe  210  is transmitted through cable  338  to data acquisition unit  26  in computer  28 . Data from rotary encoder  222  is also sent to data acquisition unit  26 . When a pulse is received from rotary encoder  222 , data acquisition unit  26  samples the value of the signal from probe  210 . Data from linear encoder  224  may also be sent to data acquisition unit  26  to indicate the axial location at which data from probe  10  is being sampled. 
         [0102]    Referring now to  FIG. 4 , with continued reference to  FIGS. 2 and 3 , a method of inspecting bore  12  using probe  10  is described and is generally indicated by reference number  400 . Starting in block  402 , acceptable characteristics and characteristics of defects of inner surface  9  within bore  12  are determined. Defect characteristics may indicate the type and size of defect and size of defects  13  on inner surface  9 , a surface roughness parameter of the surface or geometric information about the cylinder. However, other characteristics may be used in block  402 . Acceptable characteristics may be the same or similar indicators having different sizes, numbers, parameters, or geometries. In the example provided, defect characteristics are determined and used through the method. However, acceptable characteristics or both acceptable characteristics and defect characteristics may be used. 
         [0103]    In block  404 , signal patterns, including intensity thresholds, corresponding to defects or surface patterns indicative of surface defects from block  402  are determined. 
         [0104]    In block  406 , a workpiece  7  including bore  12  with inner surface  9  is provided and probe  10  is inserted into bore  12  in block  408 . In block  410 , scanning begins by directing laser beam  112  perpendicular to inner surface  9  of bore  12 . The intensity of return beam  113  that reflects perpendicular to inner surface  9  of bore  12  is measured in block  412  and is stored in block  414 . In the example provided, the intensity values of sampled points of return beam  113  are stored as a data file. 
         [0105]    In block  416 , the probe is rotated within bore  12 . The angle of rotation of probe  10  within bore  12  is measured in block  418  and is stored in block  420 . In block  422 , the depth of probe  10  within bore  12  is adjusted. The depth of probe  10  within bore  12  is measured in block  424  and is stored in block  426 . In the example provided, blocks  416  to  420  and  422  to  426  are performed simultaneously with blocks  410  to  414 . However, blocks  416  to  420  and  422  to  426  may be performed separately from each other and from blocks  410  to  414  without departing from the scope of the present disclosure. 
         [0106]    In decision block  427 , it is determined whether the travel of probe  10  within bore  12  has met predetermined conditions for the amount of bore  12  to be scanned. In the example provided, the predetermined conditions are selected to correspond to scanning the entire length of bore  12 . However, the predetermined conditions may be selected to correspond to scanning less than the entire length of bore  12 . If the predetermined conditions are not met, the method returns to block  410  where scanning will continue. If the predetermined conditions have been met, the method proceeds to block  428 . 
         [0107]    In an example of steps  410  to  427 , probe  10  is rotated in a low pitch screw path to scan the surface of the cylinder with laser beam  112  directed perpendicular to the inner surface  9  of bore  12 . Positioning machine  20  moves probe  10  towards the starting position of the scan in or near bore  12 . When probe  10  has reached the starting position linear encoder  24  sends a signal to the CNC control program. After receiving the signal from linear encoder  24 , the CNC control program begins spinning probe  10 . Rotary encoder  22  sends different signals to data acquisition unit  26  at different intervals. Index signals are sent at index intervals corresponding to a certain angular orientation of probe  10 . Sample signals are recorded at intervals predetermined from the rotary orientation of probe  10  and fixed in number during every full rotation of probe  10 . When the probe begins to spin, data acquisition unit  26  looks for the next index signal from rotary encoder  22  and begins sampling data after receiving the index signal. Data acquisition unit  26  takes and stores samples of continuously streaming data from detector  132  at every sample signal pulse from rotary encoder  22  until a predetermined number of pulses that indicate a full scan have been received. Computer  28  calculates the angle for each data point from the angle at which the index pulse is emitted, the known number of pulses per revolution and the order of a particular sample in the stored data file. However, it should be understood that the method of taking data from probe  10  may take other forms without departing from the scope of the present invention. 
         [0108]    In block  428 , a return beam pattern is determined from the intensity of return beam from block  414 , the probe angle from block  420 , and the depth of probe  10  within bore  12  from block  422 . In block  430 , the return beam pattern is compared with the signal patterns determined in block  404  and it is determined whether the return beam pattern matches the signal pattern in decision block  432 . In the example provided, if the return beam pattern matches the threshold for the signal pattern of a defect then a defect has been detected and inspection system  5  indicates that the defect is present in block  434 . The workpiece  7  will be removed from the production line for further inspection. If the return beam pattern does not match the threshold for the signal pattern of a defect then no defect is detected and inspection system  5  indicates that the defect is not present in block  436 . The workpiece  7  will continue as part of the production stream and the method is complete. It should be appreciated that blocks  428  to  430  may be performed before the predetermined conditions of block  427  have been met, and the scan may be interrupted if a defect is detected. Of course, the present invention contemplates that method  400  may be repeated to inspect other surfaces or other parts. 
         [0109]    In additional steps, even when no individual signal pattern meets the threshold for a defect, the recorded signal patterns of different inspected components may be compared to determine whether variations in signal patterns are changing monotonically over time. If the signal pattern variations are changing monotonically then the computer may generate a message to indicate a drift in the production stream that may eventually result in defects on production parts. Detecting this drift can enable corrections to the production process to be made before a defect is actually generated, thus preventing the production of defective parts. 
         [0110]    With reference now to  FIG. 5 , a schematic diagram of inspection system  500  for inspecting workpiece  502  is shown. Inspection system  500  includes probe  10 , probe shaft  14 , slip ring  16 , rotatable shaft  18 , positioning machine  20 , rotary encoder  22 , and linear encoder  24 . 
         [0111]    Workpiece  502  is mounted on part positioning fixture  504  and includes an at least partially reflective inner surface  506  that circumscribes axis  108  and defines at least one bore  507 . Workpiece  502  also includes a conical portion or conical member  508  having an angled surface  510  that is at an angle different from the angle of the inner surface  506 . In the example provided, workpiece  502  is an engine head of an internal combustion engine, bore  507  is a valve guide, and conical member  508  is a valve seat. However, it should be appreciated that other types of bores and conical surfaces within other types of workpieces may be inspected by inspection system  500 . 
         [0112]    Inspection system  500  further includes a conical mirror  512  having a conical mirror surface  514  circumscribing axis  108 . Conical mirror surface  514  defines a bore  515  that accommodates probe tip  106  of probe  10  as probe  10  moves along axis  108  during inspection. The angle of conical mirror surface  514  is selected to direct laser beam  112  from probe  10  perpendicular to angled surface  510  of conical member  508 . Conical mirror  512  is fixed to a mirror mounting and positioning fixture  516  which is attached to fixed platform  518 . In the example provided, fixed platform  518  does not move along axis  108 . 
         [0113]    With continued reference to  FIG. 5 , the operation of inspection system  500  will now be described. Laser beam  112  exits probe  10  perpendicular to axis  108  and then reflects off of conical mirror surface  514  of conical mirror  512  towards and perpendicular to angled surface  510  of conical member  508 . When laser beam  112  reaches the angled surface  510  of conical member  508 , at least a portion of laser beam  112  reflects back towards conical mirror  512  as return beam  113 . Return beam  113  then reflects off of conical mirror surface  514  towards probe  10 , where the intensity of return beam  113  and the alignment of conical member  508  relative to axis  108  are determined. In the example provided, after inspecting angled surface  510  of conical member  508 , probe  10  continues moving axially through conical mirror  512  into bore  507  where probe  10  inspects the alignment of bore  507  relative to the axis  108 . Using the measurements from conical member  508  and bore  507 , probe  10  determines whether conical surface  510  is concentric with bore  507  of workpiece  502 . 
         [0114]    In an alternative embodiment for determining whether a conical surface and a cylindrical surface are concentric, a first probe has a first mirror angled to inspect the conical surface of a valve seat and a second probe with a second mirror angled at 45° to inspect a valve guide hole. The first and second probes may be sequentially moved to the same measurement position relative to the valve guide to inspect both the valve seat and the valve guide hole. 
         [0115]    The present invention has many advantages over the prior art. A probe according to the present disclosure may scan the entire inner surface of bores having varying diameters. The probe may complete the inspection rapidly enough to be used on a production line. 
         [0116]    While the preferred modes for carrying out the invention have been described in detail, it is to be understood that the terminology used is intended to be in the nature of words and description rather than of limitation. Those familiar with the art to which this invention relates will recognize that many modifications of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced in a substantially equivalent way other than as specifically described herein.