Abstract:
An improved design of an automatic tool changing system for use with a machine tool is disclosed. The design of the tool gripper and tool holder enable reliable tool changes without requiring precise alignment of the machine tool spindle with the tool changer. In addition, the invention is modular in nature and allows an automatic tool changer to be added to a variety of machine tools in a simple and cost effective manner without extensive modification and rewiring.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to automatic tool changers for machine tools, and in particular to automatic tool changers for milling machines. 
         [0003]    2. Description of the Prior Art 
         [0004]    Milling machines are well known devices in the machine tool art. They are used extensively to perform a variety of machining operations including drilling and cutting. In milling machines a removable rotating tool, often vertically oriented, is secured in and projects downward from the lower end of a power driven spindle which is movable along one axis and mounted to a column. This tool is used to perform machining operations on a workpiece which is typically held on a horizontal table capable of movement along two or more different axes. 
         [0005]    A variety of tools are used to perform the various machining operations. Available tools include end mills, face mills, reamers, taps and drill bits. To allow successive operations using various tools to proceed automatically it is necessary to use an automatic tool changer to transfer individual tools between the machine spindle and tool storage. To facilitate this transfer tools are typically mounted in tool holders which have a standard size and shape and allow various sized tools to be easily mounted in a machine tool spindle or in tool storage. 
         [0006]    When operations with a given tool are complete the tool holder is disengaged from the spindle and transferred to tool storage. A different tool in its tool holder is then transferred from tool storage to the spindle and the next machining operation proceeds. Tool storage is often a rotatably mounted tool storage carousel. It includes means for securing tool holders. In operation the tool storage carousel is rotated until a desired position is reached at which point a tool holder is either stored or removed from the tool storage carousel. 
         [0007]    Automatic tool changers use various means for gripping tool holders during tool changes. These tool grippers also serve to secure tool holders in the tool storage carousel. In addition, these tool grippers must reliably and repeatedly locate tool holders in the proper position relative to the spindle for tool change operations. 
         [0008]    Tool grippers and tool holders are designed to function cooperatively together. In the prior art a “V” shaped grove in the tool holder typically mates with a “V” shaped ridge on the tool gripper. Complex mechanisms are often used to rigidly clamp the tool holder in the tool gripper. These mechanisms are necessary if high speed movement of the tool holder is desired, but they add significantly to the cost of the tool gripper and reduce its reliability. 
         [0009]    During operation of an automatic tool changer malfunctions or mistakes in programming can occur. These can result in costly damage to the tool changer, the tool holders, and/or the cutting tools. To reduce the possibility of damage it is known in the art to provide a means of reducing damage should a malfunction or mistake occur and cause interference. The methods employed in the prior art require additional parts and added expense, in addition they do not protect against interference from any direction. 
         [0010]    Automatic tool changers designed for high speed movement and precise alignment are too expensive for use in small shops and shops that have intermittent use, such as prototype shops and hobby shops. In addition, existing tool changers are designed with power and control signals integrated into the electrical and control systems of a specific machine tool. These tool changers can only be used on the type of machine tool the were designed for. Owners of lower cost machine tools, for which a tool changer system typically has not been designed, are therefore often unable to obtain the advantages of an automatic tool changer. 
         [0011]    For the reasons listed above owners of lower cost machine tools are typically unable to obtain the many advantages of an automatic tool changer. There therefore exists a need for an affordable and reliable tool changer that can be easily configured to work with a variety of machine tools and control systems, to serve the small shop, prototype shop, and hobby shop market. 
       SUMMARY OF THE INVENTION 
       [0012]    In view of the foregoing disadvantages inherent in the prior art the present invention provides an improved modular automatic tool changer system utilizing simple and cost effective tool grippers and tool holders. In addition break away bolts are used to minimize damage in the event of a malfunction or mistake. The simplicity of the system results in high reliability and low cost which will make the system affordable for small shop and prototype shop use. The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new and improved way of automatically changing tools which has all of the advantages of the prior art and none of the disadvantages. 
         [0013]    To achieve this purpose the present invention comprises a modular tool changer system which incorporates composite tool grippers, break away bolts, a “sprung” collet, and tool holders with a special grove to mate with the composite tool grippers. 
         [0014]    The modularity allows the tool changer to be easily configured for installation on different machines. The composite tool grippers secure tool holders for movement but allow limited flexibility to ensure tool holders can be readily aligned with the machine tool spindle. The break away bolts protect the tool changer from damage in the event of a mistake or malfunction. 
         [0015]    The composite tool grippers are composed of a rigid lower gripper and a compliant upper gripper fastened together with break away bolts. The rigid lower gripper provides structural strength and a precise vertical locating surface and is typically made of metal such as steel or aluminum. Clearance between the inner diameter of the rigid lower gripper and the outer diameter of the tool holder allows the tool holder to “float” horizontally in the composite tool gripper. The compliant upper gripper fits closely around the tool holder and secures and locates the tool holder horizontally while still allowing horizontal flexibility. The compliant upper gripper is typically made of plastic, such as polypropylene co-polymer. 
         [0016]    There has thus been broadly outlined the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention which will be described hereinafter that will form the subject matter of the claims appended hereto. 
         [0017]    In this respect, before explaining one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description and illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. 
         [0018]    Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the design of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
         [0019]    Further, the purpose of the foregoing abstract is to enable the US Patent and Trademark Office, the public generally, and especially scientists, engineers and practitioners in the art not familiar with patent or legal terms or phraseology to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way. 
         [0020]    It is therefore an object of the present invention to provide a new and improved modular automatic tool changer system which has all the advantages of the prior art and none of the disadvantages. 
         [0021]    It is another object of the present invention to provide a composite tool gripper, tool holder, and a sprung collet which work together cooperatively to improve reliability during tool changes. 
         [0022]    It is a further object of the present invention to provide an automatic tool changer system which is modular in nature and can be easily installed on a variety of machine tools. 
         [0023]    It is yet a still further object of the present invention to provide automatic tool changer system with break away bolts to minimize damage to the tool changer in the event of a mistake or malfunction. 
         [0024]    These, together with other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive material in which there is illustrated a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention will be better understood when consideration is given to the following detailed description of the preferred embodiment of the invention. This description makes reference to the following drawings: 
           [0026]      FIG. 1  is a perspective view of an automatic tool changer as utilized in the present invention mounted to a milling machine. 
           [0027]      FIG. 2  is a perspective view showing the automatic tool changer in the retracted position. 
           [0028]      FIG. 3  is a top view showing a tool holder mounted in a tool gripper, the machine spindle and collet. 
           [0029]      FIG. 4  is a section view along section line A-A of  FIG. 3  showing a tool holder mounted in a tool gripper, the machine spindle and collet. 
           [0030]      FIG. 5  is a magnified view of a tool holder mounted in a tool gripper, the machine spindle and collet shown in  FIG. 4 . 
           [0031]      FIG. 6  is a perspective view of a collet. 
           [0032]      FIG. 7  is a perspective view showing the automatic tool changer in the tool change position. 
           [0033]      FIG. 8  is a perspective view of the automatic tool changer showing a tool stored in the carousel. 
           [0034]      FIG. 9  is a top perspective view showing tool grippers mounted to the rotating plate of the storage carousel. 
           [0035]      FIG. 10  is a perspective view showing a prior art tool gripper, tool holder and tool. 
           [0036]      FIG. 11  is a top perspective view showing a tool gripper, tool holder and tool. 
           [0037]      FIG. 12  is a top view showing a tool holder and tool mounted in a tool gripper. 
           [0038]      FIG. 13  is a section view along section line B-B of  FIG. 12  of a tool holder and tool mounted in a tool gripper. 
           [0039]      FIG. 14  is a magnified view of the tool gripper and tool holder interface shown in  FIG. 13 . 
           [0040]      FIG. 15  is a schematic of the automatic tool changer power and control signals. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    Turning now to the drawing figures,  FIG. 1  shows the automatic tool changer generally designated as  10  mounted on a milling machine  12 . Mill table  14  is capable of translation in the horizontal plane and is mounted on the mill base  20 . Mill column  24  is also mounted on base  20 . The column  24  supports spindle head  26  which is capable of translation along a vertical path. Spindle head  26  supports spindle assembly  28 . Cutting tool  30  is mounted in tool holder  32  which in turn is mounted in spindle assembly  28 . 
         [0042]    Tool changer  10  is mounted to mill column  24  using support bracket  33 . Tool changer carousel  34  slides on linear rails  36  under the action of cylinder  38 . In  FIG. 1  tool changer carousel  34  is shown in the retracted position distant from spindle assembly  28 . 
         [0043]    As shown in  FIG. 2  a number of cutting tools  30  and tool holders  32  can be stored in tool changer carousel  34 . They are held by composite tool grippers  40  which are mounted to rotating plate  41 . Rotating plate  41  is rotated in the horizontal plane using conventional driving means  42  as needed to load, remove and store cutting tools  30  and tool holders  32 . 
         [0044]    As shown in  FIGS. 3 ,  4  and  5  cutting tool  30  is mounted in tool holder  32 . Tool holder  32  is mounted in spindle shaft  44  using collet  50 . Spindle shaft  44  rotates in housing  52  of spindle assembly  28 . Downward movement of drawbar  54  moves collet  50  down relative to spindle shaft  44 . This disengages tapered section  56  at the bottom of collet  50  from spindle shaft  44  and releases the straight shank  57  of tool holder  32  from the grip of collet  50 . Upward movement of drawbar  54  moves collet  50  up relative to spindle shaft  44 . This engages the tapered section  56  at the bottom of collet  50  with spindle shaft  44  and securely clamps straight shank  57  of tool holder  32  in collet  50 . 
         [0045]      FIG. 6  shows collet  50  in more detail with tapered section  56 , slots  62  and inner bore  63 . Slots  62  allow the collet to open and close as tapered section  56  is engaged and disengaged from spindle shaft  44 . 
         [0046]    As best shown in  FIG. 5  composite tool gripper  40 , composed of upper compliant gripper section  58  and lower rigid gripper section  60 , hold tool holder  32  and position it properly for tool change operations. During tool change operations it is critical that shoulder  64  on tool holder  32  is firmly located against bottom face  65  of spindle shaft  44 . This ensures that the proper vertical position of tool holder  32  and cutting tool  30  is maintained. Pocket  66  ensures that shoulder  64  does not contact collet  50 . Contact with collet  50  would not provide repeatable vertical location of tool holder  32 . 
         [0047]    To remove a cutting tool  30  from spindle assembly  28  spindle head  26  is placed at the proper height to align composite tool gripper  40  with tool holder  32  as shown in  FIG. 2 . Cylinder  38  is actuated to engage composite tool gripper  40  with tool holder  32  mounted in spindle assembly  28  as shown in  FIG. 7 . Drawbar  54 , shown in  FIG. 4 , is then moved down to disengaging tapered section  56  from spindle shaft  44  which releases tool holder  32  from the grip of collet  50 . Spindle head  26  is then raised and tool holder  32  slides out of collet  50  and is held in composite tool gripper  40  as shown in  FIG. 8 . 
         [0048]    To load a cutting tool  30  into spindle assembly  28  spindle head  26  is placed at the proper height to clear tool holder  32  as shown in  FIG. 8 . Cylinder  38  is actuated to position composite tool gripper  40  with tool holder  32  and cutting tool  30  below spindle assembly  28 . Drawbar  54 , shown in  FIG. 4 , is moved down to disengaging tapered section  56  from spindle shaft  44  which opens the inner bore  63  of collet  50  to prepare it to receive tool holder  32 . 
         [0049]    It is difficult to quickly and reliably locate tool holder  32  so that it is always centered horizontally in inner bore  63  of collet  50 . In the prior art inner bore  63  of “R-8” type collet  50  is normally straight with an inner diameter of 0.750 inches. To facilitate smooth entry of straight upper section  67  of tool holder  32  into the inner bore  63  of collet  50  the present invention, in one embodiment, utilizes a “sprung” collet. The bottom end of the inner bore  63  of collet  50  is “sprung” by bending it out between 0.004 inches and 0.012 inches. This slight bend, when combined with tapered section  84  at the top of tool holder  32 , significantly improves the smooth entry of straight upper section  67  of tool holder  32  into the inner bore  63  of collet  50 . 
         [0050]    After cylinder  38  is actuated to position composite tool gripper  40  with tool holder  32  and cutting tool  30  below spindle assembly  28  spindle head  26  is lowered and tool holder  32  slides into inner bore  63  of collet  50 . Drawbar  54  is moved up and pulls collet  50  up relative to spindle shaft  44 . This engages the tapered section  56  at the bottom of collet  50  with spindle shaft  44  and securely clamps tool holder  32  into collet  50 . Cylinder  38  is actuated to disengage composite tool gripper  40  from tool holder  32  and to move tool changer carousel  34  to the tool storage position distant from spindle assembly  28 . 
         [0051]    As shown in  FIG. 9  composite tool grippers  40  are mounted to rotating plate  41  with break away bolts  12 . Break away bolts  12  are made of nylon or another material with a lower yield strength than rotating plate  41  and rigid gripper section  60 . In the event an error during tool change operations results in interference between tool holders  32  and composite tool grippers  40  break away bolts  12  will yield and prevent damage to rotating plate  41 , tool changer  10 , and tool holders  32 . Break away bolts  12  will yield in the event of interference in the upward, downward or horizontal direction. 
         [0052]    In practice much of the difficulty and cost associated with automatic tool changers is due to the need to accurately position tool holder  32  relative to tool gripper  40  and to collet  50 . As shown in  FIG. 10  a prior art tool holder  68  has an upper tapered section  69  and a “V” grove  70 . “V” grove  70  engages ridge  72  on tool gripper  73 . Accurate positioning of tool holder  68  with respect to the machine spindle (not shown) is not required since precision tapered section  69  is pulled upward to engage the machine spindle and by virtue of the taper  69  both horizontal and vertical positioning of the tool holder  68  is readily accomplished. While this prior art design works well it is expensive and requires precise tolerances on tapered section  69  and the machine spindle. 
         [0053]    A major problem with automatic tool changers for machine tools using the less expensive R-8 type collet  50  is the correct stable positioning of the tool holder  32  relative to the machine spindle  44  and collet  50  when a tool is loaded into the spindle. The present invention accomplishes this positioning using composite tool gripper  40  and slot  74  on tool holder  32 . 
         [0054]    As best shown in  FIGS. 11 and 14  composite tool gripper  40  is composed of upper compliant gripper section  58  and lower rigid gripper section  60 . The pocket  78  of upper compliant gripper section  58  is “C” shaped and fits securely around the upper shoulder  80  of tool holder  32 . The pocket  78  of upper compliant gripper section  58  flexes out during tool holder insertion or removal and then returns to its normal position and securely holds tool holder  32 . This serves to locate tool holder  32  in the approximately correct horizontal position and allows chamfer  84  at the top of tool holder  32  to enter inner bore  63  of collet  50  as the spindle is lowered onto tool holder  32 . As straight upper section  67  of top of tool holder  32  enters into the inner bore  63  of collet  50  compliant gripper section  58  flexes as necessary and allows tool holder  32  to “float” or “swim” in the horizontal direction as needed to provide for a smooth and non-binding entry. 
         [0055]    As best shown in  FIG. 14  there is a gap  86  between the “U” shaped pocket  79  of lower rigid gripper section  60  and the outer diameter of slot  74  on tool holder  32 . Gap  86  is between 0.010 inches and 0.030 inches. Gap  86  provides clearance to allow tool holder  32  smooth and nonbinding entry into pocket  79  of rigid gripper section  60 . Gap  86  in combination with flexing of compliant gripper section  58  allows tool holder  32  to “swim” or “float” horizontally as straight upper section  67  of tool holder  32  enters into the inner bore  63  of collet  50 . This prevents binding and ensures smooth and reliable operation without the need for expensive precision tolerances on tool holder  32 , tool gripper  40  and the entire tool changer mechanism. As best shown in  FIG. 14  “U” shaped pocket  79  of lower rigid gripper section  60  is also thinner than the height of slot  74  on tool holder  32  by between 0.020 and 0.050 inches to prevent interference as tool holder  32  is inserted or removed from composite tool gripper  40 . 
         [0056]    As shown in  FIGS. 4 ,  5 , and  6  R-8 type collet  50  has an inner bore  63  which mates with straight upper section  67  of tool holder  32 . When straight upper section  67  of tool holder  32  is inserted into the inner bore  63  of collet  50  it is accurately located horizontally, but not vertically. To accomplish vertical location shoulder  64  on tool holder  32 , as shown in  FIG. 14 , must firmly engage the bottom surface  65  of spindle shaft  44  as shown in  FIG. 5 . To ensure that shoulder  64  firmly engages the bottom surface of spindle shaft  44  tool holder  32  is vertically located when flat top  82  of gap  74  on tool holder  32  rests on upper surface  76  of lower rigid gripper section  60 . These two mating horizontal surfaces ensure that tool holder  32  is accurately located vertically and also ensure that the longitudinal axis of tool holder  32  remains parallel to the axis of inner bore  63  of collet  50 . 
         [0057]    Finally, as shown in  FIG. 15 , the present invention is modular in terms of power, control signals and compressed air supply. Prior art tool changers are typically designed with power and control signals integrated into the design of a specific machine tool. They cannot be used on a different type of machine tool without extensive modification and rewiring of the machine tool and/or the tool changer. 
         [0058]    In the present invention a single USB connection between machine control computer  88  and automatic tool changer controller  94  and a single spindle interlock signal between machine spindle driver  90  and automatic tool changer controller  94  are the only connections required to the machine tool. Automatic tool changer  95  has an independent power supply and an independent controller  94 . Upon receipt of digital control signals from machine control computer  88  automatic tool changer controller  94  controls slide solenoids  96  and tool carousel stepper driver  98  as necessary. Stepper driver  98  in turn controls carousel motor  100 . Because of its modular nature the automatic tool changer of the present invention can be easily used on a variety of machine tools without extensive hardware modification.