Abstract:
Disclosed are a method and apparatus in the field of computer numerically controlled machine tools. A rotating workpiece is brought into contact with a tool, the tool being disposed in a rotating tool holder and traversing an eccentric path. By rotating the tool holder and workpiece synchronously, various characteristics forms may be produced. The method in some embodiments is useful in the turning of noncircular shapes, such as ovoid pistons and other parts.

Description:
TECHNICAL FIELD 
     The invention is in the field of computer numerically controlled machines and related methods. 
     BACKGROUND 
     Lathes have long been used to turn metal and wooden parts. In a lathe, the lathe spindle retains the workpiece via a workpiece holder mounted thereon. The workpiece holder is cause to rotate, and a cutting tool is brought into contact with the rotating workpiece to cause removal of material from the workpiece. The resulting form is symmetric about its axis of rotation. 
     In many cases, it is desired to produce forms that are not symmetric about an axis of rotation. For example, automotive pistons typically are designed to have ovoid or elliptical forms. It can be difficult to produce pistons and other parts having an ovoid shape on a lathe, and it can be difficult to produce other complex shapes on a lathe. Conventionally, in many embodiments such forms either may be milled or otherwise machined, or turned on specialized lathes. Various approaches are purportedly described in U.S. Pat. Nos. 5,313,694, 6,202,521 and 6,760,961, and U.S. Patent Publication Serial No. US2003/0209394. 
     SUMMARY 
     The invention provides in some embodiments a method that differs from the heretofore described prior patents and publication, and in other embodiments an apparatus that differs from the heretofore described prior patents and publication. In one embodiment, a method comprises providing a rotating workpiece and bringing a tool into contact with the workpiece to thereby cause material to be removed from the workpiece. The tool is offset from the rotational axis of the tool holder to thereby create eccentric rotation of said tool. In other embodiments, the invention provides an apparatus that comprises a computer control system having a computer readable medium with computer executable code disposed thereon and being operatively coupled to a tool holder and to a workpiece holder. The code comprises code for causing rotation of the tool holder, the tool holder being configured for eccentric rotation. 
     In some embodiments, the apparatus and method described herein may be used to turn noncircular shapes, such as ovoid or elliptical shapes. In some (but not necessarily all) such embodiments, it is believed that the invention may provide certain processing advantages, in particular enhanced speed and tool life. Neither the foregoing summary nor the remaining descriptions are intended to be limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a front elevation of a computer numerically controlled machine in accordance with one embodiment of the present invention, shown with safety doors closed; 
         FIG. 2  is a front elevation of a computer numerically controlled machine illustrated in  FIG. 1 , shown with the safety doors open; 
         FIG. 3  is a perspective view of certain interior components of the computer numerically controlled machine illustrated in  FIGS. 1 and 2 , depicting a machining spindle, a first chuck, a second chuck, and a turret; 
         FIG. 4  a perspective view, enlarged with respect to  FIG. 3  illustrating the machining spindle and the horizontally and vertically disposed rails via which the spindle may be translated; 
         FIG. 5  is a side view of the first chuck, machining spindle, and turret of the machining center illustrated in  FIG. 1 ; 
         FIG. 6  is a view similar to  FIG. 5  but in which a machining spindle has been translated in the Y-axis; 
         FIG. 7  is a front view of the spindle, first chuck, and second chuck of the computer numerically controlled machine illustrated in  FIG. 1 , including a line depicting the permitted path of rotational movement of this spindle; 
         FIG. 8  is a perspective view of the second chuck illustrated in  FIG. 3 , enlarged with respect to  FIG. 3 ; 
         FIG. 9  is a perspective view of the first chuck and turret illustrated in  FIG. 2 , depicting movement of the turret and turret stock in the Z-axis relative to the position of the turret in  FIG. 2 ; 
         FIG. 10  is a side elevational view of a tool holder and tool assembly useful in conjunction with certain embodiments of the invention. 
         FIG. 11  is a front view of the tool holder and tool assembly illustrated in  FIG. 10 . 
         FIG. 12  is a view taken along the Z-axis illustrating the tool as it is brought into contact with a workpiece in accordance with one embodiment of the invention. 
         FIG. 13  is a perspective view of a characteristic turned form yielded upon synchronous rotation at a relative rotational speed of 1:1. 
         FIG. 14  is a perspective view of a characteristic turned form yielded upon synchronous rotation at a relative rotational speed of 2:1. 
         FIG. 15  is a perspective view of a characteristic turned form yielded upon synchronous rotation at a relative rotational speed of 3:1. 
         FIG. 16  is a perspective view of an exemplary part that may be prepared in accordance with one embodiment of the invention. 
         FIG. 17  is a perspective view of a tool holder and tool assembly as it is brought into contact with a workpiece in another embodiment of the invention. 
         FIG. 18  is a perspective view of a tool holder and tool assembly as it is brought into contact with a workpiece in another embodiment of the invention. 
         FIG. 19  is a perspective view of a tool holder and tool assembly illustrated in  FIG. 17 , showing in phantom a range of obliqueness in the X-direction. 
         FIG. 20  is a perspective view of an alternative tool holder and tool useful in conjunction with the invention. 
         FIG. 21  is a perspective view of an alternative tool holder and tool useful in conjunction with the invention. 
         FIG. 22  is a perspective view of an alternative tool holder and tool useful in conjunction with the invention. 
         FIG. 23  is a perspective view of a turned form prepared by varying the degree of offset of a tool from the centerline of the rotating tool holder. 
         FIG. 24  is a perspective view of a part prepared by varying the relative rotational speed of the tool holder and tool during a turning operation. 
         FIG. 25  is a perspective view of a fluted tool useful in conjunction with some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Any suitable apparatus may be employed in conjunction with the methods of invention. In some embodiments, the methods are performed using a computer numerically controlled machine, illustrated generally in  FIGS. 1-9 . A computer numerically controlled machine is itself provided in other embodiments of the invention. The machine  100  illustrated in  FIGS. 1-9  is an NT-series machine, versions of which are available from Mori Seiki USA, Inc., the assignee of the present application. Other suitable computer numerically controlled machines include the NL-series machines with turret (not shown), also available from Mori Seiki USA, Inc. Other machines may be used in conjunction with the invention. 
     In general, with reference to the NT-series machine illustrated in  FIGS. 1-3 , one suitable computer numerically controlled machine  100  has at least a first retainer and a second retainer, each of which may be one of a spindle retainer associated with spindle  144 , a turret retainer associated with a turret  108 , or a chuck  110 ,  112 . In the embodiment illustrated in the Figures, the computer numerically controlled machine  100  is provided with a spindle  144 , a turret  108 , a first chuck  110 , and a second chuck  112 . The computer numerically controlled machine  100  also has a computer control system operatively coupled to the first retainer and to the second retainer for controlling the retainers, as described in more detail below. It is understood that in some embodiments, the computer numerically controlled machine  100  may not contain all of the above components, and in other embodiments, the computer numerically controlled machine  100  may contain additional components beyond those designated herein. 
     As shown in  FIGS. 1 and 2 , the computer numerically controlled machine  100  has a machine chamber  116  in which various operations generally take place upon a workpiece (not shown). Each of the spindle  144 , the turret  108 , the first chuck  110 , and the second chuck  112  may be completely or partially located within the machine chamber  116 . In the embodiment shown, two moveable safety doors  118  separate the user from the chamber  116  to prevent injury to the user or interference in the operation of the computer numerically controlled machine  100 . The safety doors  118  can be opened to permit access to the chamber  116  as illustrated in  FIG. 2 . The computer numerically controlled machine  100  is described herein with respect to three orthogonally oriented linear axis (X, Y, and Z), depicted in  FIG. 4  and described in greater detail below. Rotational axis about the X, Y and Z axis are connoted “A,” “B,” and “C” rotational axis respectively. 
     The computer numerically controlled machine  100  is provided with a computer control system for controlling the various instrumentalities within the computer numerically controlled machine. In the illustrated embodiment, the machine is provided with two interlinked computer systems, a first computer system comprising a user interface system (shown generally at  114  in  FIG. 1 ) and a second computer system (not illustrated) operatively connected to the first computer system. The second computer system directly controls the operations of the spindle, the turret, and the other instrumentalities of the machine, while the user interface system  114  allows an operator to control the second computer system. Collectively, the machine control system and the user interface system, together with the various mechanisms for control of operations in the machine, may be considered a single computer control system. In some embodiments, the user operates the user interface system to impart programming to the machine; in other embodiments, programs can be loaded or transferred into the machine via external sources. It is contemplated, for instance, that programs may be loaded via a PCMCIA interface, an RS-232 interface, a universal serial bus interface (USB), or a network interface, in particular a TCP/IP network interface. In other embodiments, a machine may be controlled via conventional PLC (programmable logic controller) mechanisms (not illustrated). 
     As further illustrated in  FIGS. 1 and 2 , the computer numerically computer controlled machine  100  may have a tool magazine  142  and a tool changing device  143 . These cooperate with the spindle  144  to permit the spindle to operate with plural cutting tools (shown in  FIG. 1  as tools  102 ′). Generally, a variety of cutting tools may be provided; in some embodiments, plural tools of the same type may be provided. 
     The spindle  144  is mounted on a carriage assembly  120  that allows for translational movement along the X- and Z-axis, and on a ram  132  that allows the spindle  144  to be moved in the Y-axis. The ram  132  is equipped with a motor to allow rotation of the spindle in the B-axis, as set forth in more detail hereinbelow. As illustrated, the carriage assembly has a first carriage  124  that rides along two threaded vertical rails (one rail shown at  126 ) to cause the first carriage  124  and spindle  144  to translate in the X-axis. The carriage assembly also includes a second carriage  128  that rides along two horizontally disposed threaded rails (one shown in  FIG. 3  at  130 ) to allow movement of the second carriage  128  and spindle  144  in the Z-axis. Each carriage  124 ,  128  engages the rails via plural ball screw devices whereby rotation of the rails  126 ,  130  causes translation of the carriage in the X- or Z-direction respectively. The rails are equipped with motors  170  and  172  for the horizontally disposed and vertically disposed rails respectively. 
     The spindle  144  holds the cutting tool  102  by way of a spindle connection and a tool holder  106 . The spindle connection  145  (shown in  FIG. 2 ) is connected to the spindle  144  and is contained within the spindle  144 . The tool holder  106  is connected to the spindle connection and holds the cutting tool  102 . Various types of spindle connections are known in the art and can be used with the computer numerically controlled machine  100 . Typically, the spindle connection is contained within the spindle  144  for the life of the spindle. An access plate  122  for the spindle  144  is shown in  FIGS. 5 and 6 . 
     The first chuck  110  is provided with jaws  136  and is disposed in a stock  150  that is stationary with respect to the base  111  of the computer numerically controlled machine  110 . The second chuck  112  is also provided with jaws  137 , but the second chuck  112  is movable with respect to the base  111  of the computer numerically controlled machine  100 . More specifically, the machine  100  is provided with threaded rails  138  and motors  139  for causing translation in the Z-direction of the second stock  152  via a ball screw mechanism as heretofore described. To assist in swarf removal, the stock  152  is provided with a sloped distal surface  174  and a side frame  176  with Z-sloped surfaces  177 ,  178 . Hydraulic controls and associated indicators for the chucks  110 ,  112  may be provided, such as the pressure gauges  182  and control knobs  184  shown in  FIGS. 1 and 2 . Each stock is provided with a motor ( 161 ,  162  respectively) for causing rotation of the chuck. 
     The turret  108 , which is best depicted in  FIGS. 5 ,  6  and  9 , is mounted in a turret stock  146  ( FIG. 5 ) that also engages rails  138  and that may be translated in a Z-direction, again via ball-screw devices. The turret  108  is provided with various turret connectors  134 , as illustrated in  FIG. 9 . Each turret connector  134  can be connected to a tool holder  135  or other connection for connecting to a cutting tool. Since the turret  108  can have a variety of turret connectors  134  and tool holders  135 , a variety of different cutting tools can be held and operated by the turret  108 . The turret  108  may be rotated in a C′ axis to present different ones of the tool holders (and hence, in many embodiments, different tools) to a workpiece. 
     It is thus seen that a wide range of versatile operations may be performed. With reference to tool  102  held in tool holder  106 , such tool  102  may be brought to bear against a workpiece (not shown) held by one or both of chucks  110 ,  112 . When it is necessary or desirable to change the tool  102 , a replacement tool  102  may be retrieved from the tool magazine  142  by means of the tool changing device  143 . With reference to  FIGS. 4 and 5 , the spindle  144  may be translated in the X and Z directions (shown in  FIG. 4 ) and Y direction (shown in  FIGS. 5 and 6 ). Rotation in the B axis is depicted in  FIG. 7 , the illustrated embodiment permitting rotation within a range of 120° to either side of the vertical. Movement in the Y direction and rotation in the B axis are powered by motors (not shown) that are located behind the carriage  124 . Generally, as seen in  FIGS. 2 and 7 , the machine is provided with a plurality of vertically disposed leaves  180  and horizontal disposed leaves  181  to define a wall of the chamber  116  and to prevent swarf from exiting this chamber. 
     The components of the machine  100  are not limited to the heretofore described components. For instance, in some instances an additional turret may be provided. In other instances, additional chucks and/or spindles may be provided. Generally, the machine is provided with one or more mechanisms for introducing a cooling liquid into the chamber  116 . 
     In the illustrated embodiment, the computer numerically controlled machine  100  is provided with numerous retainers. Chuck  110  in combination with jaws  136  forms a retainer, as does chuck  112  in combination with jaws  137 . In many instances these retainers will also be used to hold a workpiece. For instance, the chucks and associated stocks will function in a lathe-like manner as the headstock and optional tailstock for a rotating workpiece. Spindle  144  and spindle connection  145  form another retainer. Similarly, the turret  108 , when equipped with plural turret connectors  134 , provides a plurality of retainers (shown in  FIG. 9 ). 
     The computer numerically controlled machine  100  may use any of a number of different types of cutting tools known in the art or otherwise found to be suitable. For instance, the cutting tool  102  may be a milling tool, a drilling tool, a grinding tool, a blade tool, a broaching tool, a turning tool, or any other type of cutting tool deemed appropriate in connection with a computer numerically controlled machine  100 . As discussed above, the computer numerically controlled machine  100  may be provided with more than one type of cutting tool, and via the mechanisms of the tool changing device  143  and magazine  142 , the spindle  144  may be caused to exchange one tool for another. Similarly, the turret  108  may be provided with one or more cutting tools  102 , and the operator may switch between cutting tools  102  by causing rotation of the turret  108  to bring a new turret connector  134  into the appropriate position. 
     Other features of a computer numerically controlled machine include, for instance, an air blower for clearance and removal of chips, various cameras, tool calibrating devices, probes, probe receivers, and lighting features. The computer numerically controlled machine illustrated in  FIGS. 1-9  is not the only machine of the invention, but to the contrary, other embodiments are envisioned. 
     The various retainers may serve as tool or workpiece holders in accordance with the present invention. As shown, for instance, in  FIG. 10 , the tool holder  155  may comprise a holder in the nature of an adjustable boring bar holder. The tool  156 , which may be any suitable tool, is disposed in the tool holder  155  in a manner that permits the tool  156  to be offset from the center of rotation of the boring bar, as best seen in  FIG. 11  with respect to rotation  157  of the tool holder  155  and rotation  158  of the tool  156 . The rotation of the tool is thereby caused to be eccentric. The invention is not limited to the use of an adjustable boring bar, but to the contrary it is envisioned that other tool holders and configurations may be possible. 
     As shown, for instance, in  FIG. 12 , the tool is brought into contact with a workpiece  160  whereby material is removed from the workpiece. Both the tool holder  155  and workpiece  160  are rotated. In accordance with some embodiments of the invention, the rotation of the tool holder and tool are synchronous. In accordance with the present invention, and without intending to limit or affect the scope of this term as it may be used in other pending applications, synchronous rotation connotes rotation of the tool holder at a speed (revolutions per time) that is equal to or that is an integer multiple of that of the workpiece. In practice, the rotation may be synchronous within the limits of the machine, or may be synchronous to within any other desired range of tolerance. In some embodiments of the invention, the rotation of the tool holder and workpiece is not synchronous. Generally, the ratio of rotational speeds of the tool:workpiece can be expressed as 1:n, where n can be any suitable integer, fraction, or other suitable value. 
     Synchronous rotation of the tool holder and workpiece allows various characteristic turned forms to be prepared. For instance, as shown in  FIG. 13 , a rotational ratio of 1:1 yields form  166 , which comprises a generally cylindrical form having an axis  163  that is offset from the axis of rotation  167  of the workpiece  155 A. In  FIG. 14 , synchronous rotation of the tool and workpiece at a rotational ratio of 2:1 yields an ovoid form  164  on workpiece  155 B. This embodiment is useful in the preparation of engine pistons. Relative rotation at a ratio 3:1 generally yields a trilobe form  165  on workpiece  155 C, as illustrated in  FIG. 15 . It is contemplated that other non circular forms, or other forms that are asymmetric about the central axis of rotation of the workpiece, may be prepared. For instance, it is contemplated that a form similar to that shown in  FIG. 16  may be prepared. The form including two projections  168 ,  169  yielded by turning opposite ends of a rotating workpiece. 
     The tool holder and workpiece may be oriented with respect to one another in any desired manner. For instance, the tool holder may rotate about an axis that is generally perpendicular to a plane that intersects the axis of rotation of the workpiece and the point of contact of the workpiece and the tool, as illustrated in  FIGS. 12 and 17 . Alternatively, the tool holder may rotate about an axis that is oblique to a plane that intersects the axis of rotation of the workpiece and the point of contact of the workpiece and the tool. The obliqueness may have a Z-axis component, as illustrated in  FIG. 18 . In such embodiments, the degree of offset from the perpendicular may be any amount deemed or found to be suitable for use in preparing turned forms; generally, a degree of offset of up to about 45° often may be suitable. Likewise, as illustrated in  FIG. 19 , the obliqueness may have an X- or Y-axis component. In such embodiments, the degree of offset from the perpendicular may be any amount deemed or found to be suitable for use in preparing turned forms; generally, a degree of offset of up to about 15° often may be suitable. These embodiments are not mutually exclusive, and the tool and workpiece may be oblique in multiple axis. 
     In the heretofore illustrated embodiments, the tool comprises a first surface, a second surface, at least one side therebetween, and a cutting edge at the intersection of the at least one side and the first surface, as illustrated, for instance, in  FIG. 18  with reference to cutting edge  190 , first surface  191  and side surface  192 . Other tools may be employed, however. Likewise, in the heretofore described embodiments, the tool is fixed relative to the tool holder, but other configurations are possible. For instance, as shown in  FIG. 20 , the tool  173  may rotate about its own axis as the tool holder  194  rotates. The rotation may be independent of the rotation of the tool holder. Alternatively, as illustrated in  FIG. 21 , the rotation of the tool  175  may be synchronous with that of the tool holder  196 . Other embodiments for causing eccentric tool rotation are possible. For instance, as illustrated in  FIG. 22 , the illustrated piston and spring mechanism  198  may be employed to cause eccentric rotation of the tool. Other pneumatic or hydraulic or other actuation mechanisms are possible. 
     Other turned forms besides those theretofore described may be prepared. For instance, as illustrated in  FIG. 23 , the degree of relative rotation of the tool holder and workpiece has been varied from 3:1 to 2:1 as the workpiece has been fed to the tool. In  FIG. 24 , the degree of offset of the tool relative to the tool holder central axis has been varied as the workpiece has been fed. These illustrations are not intended to be limiting, but to the contrary, it is contemplated that other turned forms may be compared in accordance with the invention. 
     In some embodiments, the invention contemplates an apparatus, such as the apparatus illustrated above. Generally, the apparatus includes a computer controlled system that includes a computer readable medium having computer executable code disposed thereon. The control system is operatively coupled to the tool holder and to the workpiece holder. The code comprises code for causing rotation of the tool holder and for causing relative movement of the tool holder and workpiece in a direction having a Z-axis component. In this apparatus, the tool holder may include an adjustable offset mechanism, such as the mechanism of a boring bar tool holder, to permit adjustment of the offset between the tool and the axis of rotation of the tool holder. In a suitable apparatus, the code may include code for causing adjustment thereof. The code may include code for causing synchronous rotation of the workpiece holder and tool holder, (again, within the limits of the machine or within any other desired range of tolerance), or asynchronous rotation. The rotation may be synchronous at a relative speed of rotation of 1:1, 2:1, or 3:1, or any other suitable value. With a suitable apparatus, the code may include code for varying the degree of offset of the tool from the rotational access of the tool holder as the tool and workpiece move together in a Z-direction. In some embodiments, the code may include code for varying the degree of relative rotation of the tool holder and tool as the tool and workpiece move relative to one another in a direction having a Z-axis component. The code may include code for causing other aspects of the heretofore described methods to be performed. 
     As supplied, the apparatus may or may not be provided with a tool or workpiece. An apparatus that is configured to receive a tool and workpiece is deemed to fall within the purview of some embodiments of the invention. In other embodiments of the invention, an apparatus that has been provided with both a tool and workpiece is deemed to fall within the purview of the present invention. Except as may be otherwise claimed, the invention is not deemed to be limited to any tool depicted herein, and thus fluted tools, such as the tool shown in  FIG. 25 , may be employed. 
     It is thus seen that various turned forms, such as ovoid forms, may be prepared. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference. The description of certain embodiments as “preferred” embodiments, and other recitation of embodiments, features, or ranges as being preferred, is not deemed to be limiting, and the invention is deemed to encompass embodiments that are presently deemed to be less preferred. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended to illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Any statement herein as to the nature or benefits of the invention or of the preferred embodiments is not intended to be limiting, and the appended claims should not be deemed to be limited by such statements. More generally, no language in the specification should be construed as indicating any non-claimed element as being essential to the practice of the invention. This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. The description herein of any reference or patent, even if identified as “prior,” is not intended to constitute a concession that such reference or patent is available as prior art against the present invention.