Patent Publication Number: US-2006000101-A1

Title: Measurement probe for profilometer and method for manufacturing same

Description:
FIELD OF THE INVENTION  
      The present invention relates to surface measurement equipment such as a profilometer which measures surface profiles with high precision, and more particularly to a probe structure used for a profilometer and method for manufacturing the probe structure.  
     BACKGROUND  
      Measurement of surface topography or surface roughness is very important in manufacturing of small sized products such as optical lenses used in optical communication, pickup lenses for optical disks, and molds for making such lenses. Generally, methods for measuring surface topography include the contact mode measurement method and the non-contact mode measurement method. The contact mode measurement method detects a surface of an object being measured by contacting a probe of a piece of measurement equipment (such as a profilometer, also named a profiler) with the surface of the object, and moving the probe along the surface at a predetermined velocity to obtain data pertaining to the surface. Generally, a contact-type profiler employs a probe having a tip end moving along the surface being measured. Unevenness of the surface causes the probe to move up and down, and these displacements are converted into optical or electrical signals. Then the signals are magnified and processed by a computer to obtain a trace of the profile or surface roughness of the surface measured.  
      One important factor affecting the precision of contact-type profilometers is the geometrical shape and size of the probe, especially the shape and size of the tip end of the probe that directly contacts the surface to be measured. Generally, a probe employs a spherical tip end, which generally comprises a ruby ball with a very small diameter (for example, less than 1 mm). The smaller the diameter of the tip end, the higher the precision of the profilometer. A relatively large tip end lowers the precision of measurement, and also increases the tolerance, i.e., the difference between the true value and the measured value. The theoretical ideal diameter of the tip end is zero. According to modern technologies, typical diameters of tip ends are in the scale of micrometers. In addition, the higher the roundness of the tip end, the higher the precision of the profilometer.  
      Besides the tip end, a probe further includes a holder. The holder has a long and narrow shape, and the tip end is fixed on the holder. In general, it is difficult to integrally make a probe having a tip end (such as a ruby ball) with a high roundness. Instead, for a typical probe, the tip end and the holder are first made separately. Then the tip end is attached to the holder to form the unified probe.  
      In contact-mode measurement equipment such as a profilometer, the probe has to move along a surface of the object to be measured. Hence, the probe needs to satisfy the following requirements: 
          (1) the tip end of the probe has a small diameter and high roundness in order to improve the measurement precision;     (2) the tip end is firmly jointed with the holder in order to prevent separation; and     (3) the tip end of the probe protrudes sufficiently outward, in order to maximize the effective contact surface of the tip end.        

      Referring to  FIG. 2 , a conventional probe  10  for measurement equipment includes a tube member  12 , and a sphere member  15  attached to the tube member  12 . The tube member  12  and the sphere member  15  are manufactured separately. The tube member  12  is hollow, defining an inner channel  13  therein. Preferably, the sphere member  15  has a high roundness. The sphere member  15  is pressed into the inner channel  13  of the tube member  12  and fixed therein. This means that the sphere member  15  and the tube member  12  have to be made and sized very precisely, so that a diameter of the sphere member  15  mates with a diameter of the inner channel  13 . This requirement can significantly increase the difficulty and cost of manufacturing the probe  10 . In addition, as seen in  FIG. 2 , a major portion of the sphere member  15  is received in the channel  13  and covered by the tube member  12 , with only ⅓ or less of the surface area of the sphere member  15  being exposed outside the tube member  12 . Thus, an effective contact surface of the sphere member  15  for contact with a surface of an object to be measured is limited. If an object having a deep groove or slot is measured, the tube member  12  is liable to contact sidewalls of the groove or slot, thereby preventing the sphere member  15  from reaching the surface in the groove or slot to be measured.  
      Referring to  FIG. 3 , another conventional probe  20  includes a tube member  22  and a sphere member  25 . The tube member  22  defines an inner channel  23  therein, and the sphere member  25  is adhered on an end of the tube member  22  by an adhesive  26 . The probe  20  has the advantage of a major surface portion (greater than ½) of the sphere member  25  being exposed as an effective contact surface. However, adhesion provided by the adhesive  26  is limited, because an adhesive interface area between the sphere member  25  and the channel  23  is relatively small. Hence, the sphere member  25  is liable to separate from the tube member  22 , especially when an object being measured has a rough surface. In particular, the sphere member  25  is likely to sustain transverse forces until it detaches from the tube member  22 .  
      Accordingly, what is needed is a probe structure for a profilometer which overcomes the above disadvantages. In particular, a probe which has high measurement precision and improved structural stability.  
     SUMMARY  
      One embodiment of the present invention provides a probe for use in surface measurement equipment such as a profilometer. The probe comprises a holder, a head member, and a connecting member connecting with the holder and the head member respectively. The connecting member has a first end and a second end. The holder has a first recess at one end thereof for receiving the first end of the connecting member. The head member has a second recess spanning from an outer surface to a central portion thereof for receiving the second end of the connecting member. The first end of the connecting member defines a shape similar to that of the first recess of the holder and is fixed in first recess by adhering, welding or doweling. The second end of the connecting member defines a shape similar to that of the second recess of the head member and is fixed in the second recess by adhering or welding. Hence, the head member of the probe is jointed with the holder via the connecting member firmly and stably, and an effective contact surface of the head member is increased for contacting with an object to be measured. In addition, most transverse resist forces produced in use is absorbed by the connecting member, therefore the problem of separation or disconnection of the head member from the holder is avoided.  
      A method for making the probe comprises steps of: making a holder defining a first recess at one end thereof; making a head member defining a second recess spanning from an outer surface of the head member to a central portion of the head member; making a connecting member having a first end and a second end; fixing the first end of the connecting member in the first recess; and fixing the second end of the connecting member in the second recess.  
      Other structures, methods, features, and advantages of the present invention will be or become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such additional structures, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a probe according to a preferred embodiment of the present invention;  
       FIG. 2  is a cross-sectional view of a first conventional probe structure; and  
       FIG. 3  is a schematic, cross-sectional view of a second conventional probe structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made to the drawings to describe a preferred embodiment of the present invention in detail.  
      Referring to  FIG. 1 , according to a preferred embodiment of the present invention, a probe  30  is for use in high precision surface measurement equipment such as a profilometer. The probe  30  includes a holder  32 , a head member  35 , and a connecting member like a dowel  37  having a first end and an opposite second end. Preferably, the holder  32  is a tubular piece. The holder  32  defines a first recess  33  at one end thereof, for receiving the first end of the dowel  37 . The first recess  33  has a configuration similar to that of the first end of the dowel  37 . Preferably, the first recess  33  of the holder  32  is shaped as a cylinder, and has a diameter the same as or a little greater than that of the first end of the dowel  37 . The head member  35  is a spherical piece, and defines a second recess  351  therein for receiving the second end of the dowel  37 . The second recess  351  spans from an outer surface of the head member  35  to a central portion thereof, and has a shape similar to that of the second end of the dowel  37 . A diameter of the second recess  351  is the same as or a little greater than that of the second end of the dowel  37 . Preferably the head member  35  has a high roundness, and typically has a diameter in the range from a plurality of micrometers to a plurality of millimeters. The dowel  37  is preferably shaped as a cylinder, and has a diameter the same as or a little greater than that of the first recess  33  of the holder  32 . A length of the dowel  37  is at least slightly greater than a depth of the second recess  351  of the head member  35 . The first end of the dowel  37  is received in the first recess  33  of the holder  32  and fixed therein; for example, by adhering, welding, or interference fitting. The second end of the dowel  37  is received in the second recess  351  of the head member  35  and fixed therein; for example, by adhering or welding.  
      Preferably, the holder  32  is made of steel, especially tungsten steel, or a super-hard alloy material. The head member  35  may be made of, for example, metal, ruby, ceramic, or a super-hard alloy material. The dowel  37  may be made of metal or a super-hard alloy material.  
      It is noted that the dowel  37  may instead have other shapes, such as being prism-shaped with one or more triangular cross-sections and/or one or more rectangular cross-sections, or being polygonal. Whatever shape is provided for the dowel  37 , the shapes of the first recess  33  of the holder  32  and the second recess  351  of the head member  35  are configured accordingly.  
      A method for making the probe  30 , and advantageous aspects of the present embodiments, will be described below.  
      The holder  32 , dowel  37  and head member  35  are manufactured separately. As an example, the holder  32  and the dowel  37  can be made by an ordinary mechanical machining process. The holder  32  is machined to define the first recess  33  therein, which is then mated with the first end of the dowel  37 . The head member  35  is preferably made as a spherical piece having a high roundness. Then the second recess  351  is formed in the head member  35  by a precision machining technology, such as diamond tool milling, grinding, ultrasonic machining, discharge machining, or laser machining.  
      Then in assembly, the second end of the dowel  37  is inserted into the second recess  351  of the head member  35 , and is fixed therein by adhesive or welding. If the dowel  37  is fixed by adhesive, preferably, an adhesive is coated on the second end of the dowel  37  prior to insertion of the second end of the dowel  37  into the second recess  351 . After the adhesive is solidified, the dowel  37  and the head member  35  are fixed as one. Because the second end of the dowel  37  is inserted into the head member  35 , an adhesive interface are between these two components is significantly increased in comparison with conventional structures. Therefore, a joint strength of and stability between the dowel  37  and the head member  35  are increased. In addition, the dowel  37  takes up minimal space of the outer surface of the head member  35 . Therefore an effective contact surface of the head member  35  for contact with an object to be measured is increased. Moreover, in use, a resisting transverse force produced by a rough surface of the object being measured is absorbed by the dowel  37 . Hence, the problem of separation or disconnection often occurring in conventional structures is avoided.  
      Finally, the first end of the dowel  37  is inserted into the first recess  33  of the holder  32 , and fixed therein by adhesive, welding, or interference fitting. For reasons similar to those described above, the dowel  37  is firmly jointed with the holder  32 , with minimal risk of these two components separating.  
      The probe  30  as described in the preferred embodiment can be used in various surface measurement equipment, such as a profilometer.  
      It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.