Abstract:
A micrometer, including a constant force drive spring actuator configuration, is disclosed which comprises a frame, an anvil, a spindle, a linear displacement sensor that senses a displacement of the spindle, and an actuator including a button which is configured to move the spindle toward or away from the anvil. The spindle drive is attached to a constant force spring actuator comprising at least one constant force spring coil extending toward the spindle and attached between the spindle and the frame such that the sum of their forces drives the spindle toward the anvil with an approximately constant force. In some embodiments, the constant force spring actuator comprises at least two parallel constant force spring coils, extending in parallel toward the spindle. The constant force spring may be made more compact, exert a greater force, and have an extended life relative to known configurations.

Description:
FIELD 
       [0001]    The present disclosure relates generally to handheld micrometers, and more specifically, to a handheld micrometer with a constant force spring actuator for moving a spindle into contact with a workpiece. 
       BACKGROUND 
       [0002]    Various micrometer devices are known in the art for performing high precision measurements of workpieces using a handheld mechanism. For example, U.S. Pat. Nos. 1,132,704; 3,849,890; 4,485,556; 4,561,185; and 8,091,251 (referred to herein as the &#39;704, &#39;890, &#39;556, &#39;185, and &#39;251 patents), each of which is hereby incorporated by reference in its entirety, disclose micrometer devices. In particular, modern micrometers such as that disclosed in U.S. Pat. No. 5,495,677 (the &#39;677 patent), which is hereby incorporated by reference in its entirety, comprise a linear digital sensor for determining measurements, rather than relying on accurate micrometer threads in combination with a rotary position sensing device. Using a linear digital sensor eliminates the need to use accurate or fine pitch threads in order to drive the micrometer. 
         [0003]    Various methods are known for providing constant force in hand measurement tools. For example, U.S. Pat. No. 4,035,922 (the &#39;922 patent), which is hereby incorporated by reference in its entirety, discloses a digital micrometer or gauge which includes a constant force spring to drive two anvils toward each other. However, this particular arrangement is bulky and prone to a potentially short lifetime. Furthermore, if this design were to be more compact, the constant force spring may not provide enough force to properly drive the anvils toward each other. 
       SUMMARY 
       [0004]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0005]    In various embodiments described herein , a micrometer quickly drives a spindle to a desired position with limited motion on the part of the user while driving the spindle toward the anvil with a constant force. Various embodiments described herein include a compact design, a greater force provided by a constant force spring arrangement and an extended life of spring coils relative to known configurations. Various embodiments described herein provide ergonomic, rapid, and convenient functionality for users. 
         [0006]    For example, disclosed herein is a micrometer including a constant force spring actuator configuration which is more compact, exerts a greater force, and has an extended life relative to known configurations such as the &#39;922 patent. In various embodiments, the micrometer comprises a frame comprising: an anvil, a spindle, a linear displacement sensor that senses a displacement of the spindle, and an actuator including a button attached to a spindle which is configured to move the spindle toward or away from the anvil. The spindle is attached to a constant force spring actuator comprising at least two constant force spring coils extending in parallel toward the spindle and attached between the spindle and the frame such that the sum of their forces drives the spindle toward the anvil with a constant force. 
         [0007]    In some embodiments, each of the spring coils of the constant force spring actuator may provide a force of at least 0.05 N. 
         [0008]    In some embodiments, the constant force spring coils may comprise material which is at most 0.4 mm thick. 
         [0009]    In some embodiments, the constant force spring coils may comprise material which is longer than the range of the spindle. 
         [0010]    In some embodiments, the constant force spring actuator may comprise a width which is at most 25 mm. In some embodiments, when fully wound, the constant force spring actuator may comprise a diameter which is less than 35 mm. 
         [0011]    In some embodiments, the constant force spring coils may be parallel to the direction of the spindle. 
         [0012]    In some embodiments, the at least two parallel constant force spring coils may extend into a handle of the micrometer alongside the spindle when the spindle is retracted into the handle. 
         [0013]    In another embodiment, the micrometer comprises a frame comprising: an anvil, a spindle, a linear displacement sensor that senses a displacement of the spindle, and an actuator including a button attached to a spindle which is configured to move the spindle toward or away from the anvil. The spindle is attached to a constant force spring actuator comprising at least one constant force spring coil extending toward the spindle and attached between the spindle and the frame such that it drives the spindle toward the anvil with a constant force. The at least one constant force spring coil extends into a handle of the micrometer alongside the spindle when the spindle is retracted into the handle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a diagram of a basic micrometer gauge which may be adapted to the principles disclosed herein; 
           [0016]      FIG. 2  is a cross-sectional diagram of the micrometer gauge shown in  FIG. 1 , showing further details; 
           [0017]      FIG. 3  is a cross-sectional diagram of the micrometer gauge shown in  FIGS. 1 and 2 , showing further details; 
           [0018]      FIG. 4  is a diagram of a set of constant force spring coils shown in  FIG. 3 ; 
           [0019]      FIG. 5  is a cross-sectional diagram of the micrometer gauge shown in  FIGS. 1 through 4 ; and 
           [0020]      FIG. 6  is an exploded isometric diagram of the micrometer gauge shown in  FIGS. 1 through 5 , showing further details. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  is a diagram of a basic micrometer gauge which may be adapted to the principles disclosed herein. The micrometer of  FIG. 1  may incorporate elements of the commonly assigned &#39;677 patent and may additionally be adapted to comprise elements described in  FIGS. 3 and 4 . 
         [0022]    In  FIG. 1 , a digital display micrometer gauge  1  has a main body  2  formed as a closed, water/dust proof structure. A spindle  3  is adapted to project from and retract into main body  2 . A cover member  8 , seen in  FIG. 1 , is provided on the front surface of U-shaped main frame  4 . A digital display device  9  and a plurality of operating switches  10  are provided on the front surface of cover member  8 . 
         [0023]    The U-shaped main frame  4  has two outwardly extending ends defining an opening with an anvil  11  disposed at one of the ends as seen in  FIG. 1 . At the other end of main frame  4 , spindle  3  is supported such that it can be axially displaced by sliding an actuator button  17 . One end of spindle  3  is adapted to abut against anvil  11 . A handle element  16  and an end cap  27  cover the connection between the actuator button  17  and the spindle  3 . 
         [0024]      FIG. 1  shows lines C-C and D-D. Other figures show cross-sectional diagrams along these lines. 
         [0025]      FIG. 2  is a cross-sectional diagram of the micrometer gauge  1  shown in  FIG. 1  along line D-D. As shown in  FIG. 2 , an electronics board  8 ′ is placed between the cover member  8  and the main body  2 . The electronics board  8 ′ is configured for processing position signals indicative of a position of the spindle  3  relative to the anvil  11 , as well as providing signals for displaying an indication of this position on the digital display device  9 , and receiving and processing input from the operating switches  10 . 
         [0026]      FIG. 3  is a cross-sectional diagram of the micrometer gauge  1  shown in  FIGS. 1 and 2  along a line A-A (shown in  FIG. 2 ) which goes through spindle  3 , showing further details. As seen in  FIG. 2  and  FIG. 3 , main body  2  includes a U-shaped main frame  4 , a spindle driving mechanism  5  (or spindle drive) for causing spindle  3  to advance and retreat, and a position transducer  6  for detecting the displacement amount of spindle  3 . The spindle driving mechanism  5  includes the actuator button  17  and a constant force spring actuator  21 . Position transducer  6  is a linear encoder, arranged inside U-shaped main frame  4  through the intermediation of gap control mechanism (not shown) and a main scale  31  (see  FIG. 6 ). Main scale  31  is attached to the spindle  3  through the intermediation of a scale mounting member  30 . The scale mounting member  30  and the spindle  3  move inside of the handle element  16 , which is closed by an end cap  27 . The spindle  3  is generally surrounded by a bushing  28 , which seals the end of the main frame  4 . 
         [0027]    Position transducer  6  is connected to digital display device  9 , shown in  FIG. 1 , through conventional electric devices, such as a counter and CPU (not shown). The position transducer  6  employs a photoelectric type encoder as schematically seen in  FIG. 2 . For example, the photoelectric type encoder disclosed in U.S. Pat. No. 5,026,164, the disclosure of which is incorporated herein by reference, could be employed. The position transducer  6  may also employ a capacitive or inductive type encoder in alternative embodiments. 
         [0028]    Referring again to  FIG. 3 , an actuator button  17  is attached via a pin  18  to a bushing  19  which is attached to the scale mounting member  30 . The actuator button  17  is configured to move the spindle  3  toward or away from the anvil  11 . The scale mounting member  30  is attached to the constant force spring actuator  21  by a screw  25 . The constant force spring actuator  21  comprises a set of constant force spring coils  22  extending in parallel toward the spindle  3  and attached between the spindle  3  and the main frame  4  such that the sum of their forces drives the spindle  3  toward the anvil  11  with a constant force. The constant force spring actuator  21  additionally comprises a hub  23  and a shoulder screw  24 . The set of constant force spring coils  22  is wound around the hub  23 , which is secured to the main frame  4  with the shoulder screw  24 . In the embodiment shown in  FIG. 3 , the actuator button  17  is a thumb slider which may be ergonomically driven by a user&#39;s thumb. In some embodiments, the set of constant force spring coils  22  comprises at least two constant force spring coils. 
         [0029]    In some embodiments, a single constant force spring coil may provide sufficient force to drive the spindle  3 . A single constant force spring made from some materials (e.g., beryllium copper alloys or composite materials) may provide a sufficient amount of force for driving the spindle  3  as well as an acceptable lifetime. It should be appreciated that advancements in these materials may make a single constant force spring coil more desirable. However, in some embodiments a single constant force spring coil, which fits in the space allotted by the main frame  4 , may not provide enough force while at the same time allowing a sufficient lifetime of driving the spindle  3 . Therefore, as shown in  FIG. 3  and  FIG. 4 , two or more parallel constant force spring coils may be simultaneously wound around the hub  23  in order to provide a sufficient amount of force and, by splitting the force between multiple springs, increase the expected lifetime. In some embodiments, each of the spring coils of the constant force spring actuator provides a force of at least 0.05 N. Increasing the diameter of hub  23  reduces the stress in the constant force springs, thereby increasing the lifetime. It should be appreciated that there is a maximum diameter of the hub  23  and the set of constant force spring coils  22  that will fit in the micrometer main frame  4 . It should be appreciated that there is a practical limit to the number of constant force spring coils which may be wound around the hub  23 , as each spring coil increases the diameter of the constant force spring actuator  21  when fully wound. In some embodiments, when fully wound, the constant force spring actuator  21  comprises a diameter which is less than 35 mm. Additionally, the length of each spring coil may also be a limiting factor, as each turn around the hub  23  increases the overall diameter of the constant force spring actuator  21 . In some embodiments, the constant force spring actuator  21  comprises material which is at least 5 mm longer than the range of the spindle  3 . For example, a typical micrometer may include a spindle which moves through a range of 30 mm, and, therefore, in such embodiments, when fully extended each spring coil is less than 35 mm in length. The width of each spring coil must be considered for space constraints, as there is limited width between the electronics board  8 ′ and the main frame  4 . It should be appreciated that there is a practical limit to the width of the set of constant force spring coils  22  which allows the spring coils to fit in the micrometer main frame  4 . In some embodiments, the constant force spring actuator  21  comprises a width which is at most 25 mm. Spring coils are generally rated to a limited lifetime, for the number of times they may be wound and unwound before mechanical failure. For example, series L springs from Vulcan Spring of Telford, Pa. are rated to 25,000 cycles. The life cycle rating is generally reduced if spring coils are redirected by a pin or the like, because this puts additional stress on the constant force springs. In order to maintain the rated lifetime of the constant force spring actuator  21 , in some embodiments, the constant force spring coils are parallel to the direction of the spindle. Therefore, constant force spring coils which are parallel to the direction of the spindle are included in an embodiment. 
         [0030]      FIG. 4  is a diagram of the set of constant force spring coils  22  of  FIG. 3 . In the embodiment shown in  FIG. 4 , the set of constant force spring coils  22  comprises constant force spring coils  22 A,  22 B and  22 C. It should be appreciated that this embodiment is exemplary only and not limiting. Any set of constant force spring coils which comprises at least two constant force spring coils may be used in accordance with the principles described herein. Furthermore, it is desirable in some embodiments, for such a set of constant force spring coils to follow the parameters described with respect to  FIG. 3  and described in further detail with respect to  FIG. 5 . 
         [0031]      FIG. 5  is a cross-sectional diagram of the micrometer gauge  1  shown in  FIGS. 1 through 4  along line C-C. The thickness of each constant force spring coil, or more specifically, the sum of their thicknesses, is a limiting factor in the design of the micrometer gauge  1 . As shown in  FIG. 5 , the set of constant force spring coils  22  comprises spring coils with thicknesses which add up to a total thickness t. The total thickness t must be small enough such that the end of the screw  25  fits between the scale member  30  and the main frame  4 . In some cases, this may leave a very tight tolerance of space to provide a functional micrometer. In some embodiments, each coil of the set of constant force spring coils  22  may comprise material which is at most 0.4 mm thick. Thus, in an embodiment with two parallel constant force spring coils, the total thickness t is less than 0.8 mm, or an embodiment with three coils (e.g., the embodiment shown in  FIG. 4 ), the total thickness t is less than 1.2 mm.  FIG. 6  is an exploded isometric diagram of the micrometer gauge  1  shown in 
         [0032]      FIGS. 1 through 5 , showing additional details. As shown in  FIG. 6 , the actuator button  17  is configured to move the spindle toward or away from the anvil as it moves the pin  18  through a groove  20  in the handle element  16 . 
         [0033]    Numerous variations in the illustrated and described arrangements of features and sequences of operations will be apparent to one skilled in the art based on this disclosure. 
         [0034]    Thus, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the claimed subject matter.