Abstract:
A quill style drilling/milling end effector with high tool positioning accuracy, a pressure foot with fast response in force and displacement feedback, and with automatic mounting and dismounting, normality sensing, and through the tool coolant delivery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to machine tools and, more particularly, to end effectors typically used with robots. 
       PRIOR ART 
       [0002]    Traditionally, the machining or other like work on large bodies or assemblies has been accomplished with even larger equipment that has a bed for receiving or holding the body and for supporting and driving tools at a point or points in the space surrounding the body. In more recent times, industrial robots have been available to position and support tools for operation on large bodies. Conventional machines, whether a large monument type, or a gantry type have limitations on the accuracy by which they can position and hold a tool with respect to the body being machined or otherwise operated on. As technology has advanced, there has developed a need for precision positioning of tooling or other instrumentalities that exceeds the capability of conventional equipment to machine large parts, bodies or assemblies. The size and mass of the machinery as well as temperature conditions are factors that contribute to making the task of holding accurate machining tolerances difficult if not impractical. Further, active joints, bearings, slides, couplings, and the like can introduce lash, again, making precise positioning of tooling elements difficult. 
         [0003]    Applications of a robotic end effector can benefit from or require a pressure foot that first engages the work before a tool is deployed. It can be desirable to automatically remove a pressure foot from an end effector, for example, when its function is not required, when automatic tool changes require removal of the pressure foot, or when a different pressure foot is needed. 
         [0004]    Some applications require that the end effector extend a tool towards the workpiece in a direction that is precisely normal to the surface to be worked. Many applications can require or benefit from coolant delivery through the tool. Weight of an end effector is a disadvantage in robotic applications since the size of a robot is typically dependent on the weight it must support and, generally, the larger the robot, the slower and less accurate it is. It is, therefore, desirable that the elements and instrumentalities employed to obtain these and other beneficial features allow an end effector to be compact and low in mass. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides an improved quill style drilling/milling end effector with high tool positioning accuracy, a pressure foot with fast response in force and displacement feedback and with automatic mounting and dismounting, normality sensing, and through the tool coolant delivery. Accurate tool positioning is accomplished with a micro positioner that is interposed between the end effector carrier, typically a robot arm or a gantry machine, and the tool spindle. The micro positioner can be operated after the macro positioning carrier has located the tool spindle as close as practical to the site at which work is to be performed. This arrangement enables the micro positioner to eliminate imprecision in the carrier positioning of the end effector relative to the specified machining location. 
         [0006]    In a preferred arrangement, the micro positioner comprises two slides arranged with axes perpendicular to one another and perpendicular to the spindle axis of the end effector, thus affording two additional positioning axii to the host robot or other carrier. The slides are arranged on-center with the drilling/milling axis of the end effector, thereby avoiding excessive eccentric loading of the end effector and simplifying position control. 
         [0007]    The disclosed micropositioning system works with a pressure foot device that effectively couples and stabilizes the robot arm relative to the workpiece before the micro positioner is operated. This arrangement enables the micro positioner to reliably eliminate errors in the robot positioning of the end effector relative to the desired machining location. 
         [0008]    The disclosed end effector accessories are uniquely developed and arranged for a quill style end effector and achieve benefits that are not readily obtainable with other drilling/milling end effector designs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a front isometric view of an end effector unit embodying aspects of the invention; 
           [0010]      FIG. 2  is a rear isometric view of the end effector unit; 
           [0011]      FIG. 3  is a fragmentary top view of the end effector unit showing details of the micro positioner; 
           [0012]      FIG. 4  is a fragmentary side view of the end effector unit showing the micro positioner; 
           [0013]      FIG. 5  is a view of a tool changer with the master and tool sides separated; 
           [0014]      FIG. 6  is a cross-sectional view of a ball coupling of the tool changer of  FIG. 5 ; 
           [0015]      FIG. 7  is a front perspective view of a second embodiment of an end effector unit; 
           [0016]      FIG. 8  is a diagram illustrating the relative positions of certain elements of the end effector of  FIG. 7 ; 
           [0017]      FIG. 9  is a longitudinal cross-sectional view of the spindle area of the end effector of  FIG. 7 ; 
           [0018]      FIG. 9A  is an enlarged cross-sectional view of the rear end of the end effector of  FIG. 7 ; and 
           [0019]      FIG. 9B  is an enlarged cross-sectional view of the spindle end of the end effector of  FIG. 7 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring now to  FIGS. 1 and 2 , a drilling/milling end effector unit  10  is adapted to be supported by an industrial robot through a tool side  11  of a tool changer. The illustrated end effector  10  is similar in construction to that disclosed in U.S. Pat. No. 7,547,169, the disclosure of which is incorporated herein by reference. The end effector unit  10  has a spindle indicated in phantom at  12  rotatable about an axis  15 . The forward end of the spindle  12  is surrounded by a hollow nose or cone  13 . 
         [0021]    An electrically driven servomotor  16  at the top of the unit  10  drives an axial quill feed through a belt within a housing  17 . Another electrically operated servomotor  18  at the bottom of the unit  10  drives the spindle  12  through an associated belt. The end effector unit  10  includes a frame or pressure bridge  19 , U-shaped in plan view, to which the tool changer  11  is attached and which supports the remaining components of the unit. The tool changer tool side  11 , which can be a commercially available unit such as manufactured by ATI Industrial Automation, Inc. of Apex, N.C. 27539, USA, is fixed on a rear face of the pressure bridge  19 . The tool side  11  is arranged to automatically couple with a complementary master side of a tool changer fixed to the end of an arm of an industrial robot such as manufactured by KUKA Roboter GmbH. The changer tool side  11 , in addition to automatically coupling the pressure bridge  19  to a robot arm, provides for utilities including electrical signals, air pressure, and coolant to be supplied to the end effector unit  10 . A vacuum tube  21  runs between the interior of the spindle nose  13  and the changer tool side  11  for collecting machining chips and debris. 
         [0022]    The spindle nose  13  is removably attached to a plate or pressure foot  23  by a tool changer  51 . The tool changer  51  is shown in greater detail in  FIGS. 5 and 6  and discussed below. The pressure foot plate  23  is carried on four guide rods  26  distributed about and parallel to the spindle axis  15 . The guide rods  26  slide in linear bearings  27  fixed to the front of the pressure bridge frame  19  enabling the pressure foot  23  and spindle nose  13  to move in the axial direction of the spindle  15  relative to the frame. An associated electrically operated servomotor  31  fixed on the frame  19  rotates a helical screw shaft  32  in a ball nut  33  fixed on the plate  23  to positively mechanically extend or retract the plate and spindle nose  13 . The servomotor  31 , operated by the end effector controller, feeds back electrical signals through the tool changer represented by the tool side  11  to the end effector controller that indicate the angular displacement of the motor  31  from a reference position and the torque being applied by the motor. These signals are essentially instantaneous indications of the extension of the spindle nose  13  and the force being applied by the spindle nose. The speed or response of these signals can be used by the end effector controller to achieve a fast machine cycle time. Moreover, the spindle nose extension or displacement data supplied by the servomotor  31  can be compared with that provided by a linear transducer connected between the pressure bridge  19  and the pressure foot plate  23  to detect an error in either of these signals. 
         [0023]    Mounted on an inner face of a rear wall  36  of the pressure bridge frame  19  are two slides  37 ,  38 . Each slide  37 ,  38  has a table  39 ,  40  capable of moving in an associated plane parallel to the wall  36  and perpendicular to the spindle axis  15 . A first slide  37  moves vertically, in the orientation of the unit  10  shown in  FIGS. 1 and 2 , relative to the pressure bridge frame  19  on linear bearings  41  supported directly on the wall  36 . Precision displacement of the slide  37  is produced by an associated electrically operated servomotor  42  mounted on the frame  19 . The second slide  38  is mounted on the first slide  37  and moves vertically with the first slide and horizontally relative to the first slide and the frame  19  on linear bearings  43  carried on the first slide table  39 . Precision displacement of the second slide  38  is produced by an associated electrically operated servomotor  44  mounted on the first slide  37 . 
         [0024]    Together, the slides  37 ,  38  and actuators or servomotors  42 ,  44  comprise a two-axis micro positioner  45  that can adjust the spindle  12  along two mutually perpendicular axiis that are each perpendicular to the spindle axis  15 . Each of the slides  37 ,  38  is capable of moving a total of, for example, 1″ along its respective axis. Ideally, a spindle housing  46  fixed to the slide table  40  is located so that when each of the slides  37 ,  38  is in its center position, the spindle axis  15  is coincident with these center positions. Together, the slides  37 ,  38  and associated servomotors  42 ,  44  provide adjustment in any direction in a plane perpendicular to the spindle axis  15 . While the displacement available at the slides  37 ,  38  is limited, this displacement provides an adjustability much greater than the positioning accuracy of a typical robot sized to handle the weight of the end effector  10 . 
         [0025]    More specifically, the end effector unit  10  can be mounted on the end of a robot arm so that the end effector can be coarsely brought into working position relative to a workpiece. The workpiece can be relatively large in comparison to the unit  10 , being, for example, at least several times as large. A robot large and strong enough to support the unit  10  throughout a major part of the space surrounding a large workpiece may have limited accuracy in positioning the unit, and such accuracy may not be sufficiently precise to satisfy the manufacturing specifications of the large workpiece. A robot of a size adequate to handle the end effector unit may have, for example, a positional accuracy of about ±0.020″. The micro positioner  45  of the invention overcomes this positioning limitation of a robot by precisely locating the end effector unit  10  relative to a workpiece within, for example, about ±0.0002″ in a plane generally parallel to the workpiece surface. Various techniques, including use of an optical target, can be used by the robot and end effector unit controller or controllers to operate the micro positioner  45  to precisely locate the spindle axis  15  in space relative to the workpiece. When a controller determines a positioning error smaller than that ordinarily taken up by a robot or other manipulator of the end effector unit  10 , the controller can energize either or both of the micro positioner servomotors  42 ,  44  to precisely align the spindle axis  15  with the work site. During the time that a positioning error is found and while the micro positioner  45  is being operated, the pressure foot plate  23  operating through the spindle nose  13  serves as a bridge between the robot and the workpiece with enough force to effectively lock these objects together. This same stabilization effect of the extended pressure foot plate  23  is utilized during actual drilling/milling operation of the end effector  10 . With the pressure foot plate  23  and spindle nose  13  extended against the workpiece, for example, laminations of material of the workpiece can be held in contact with one another to obtain uniform results. 
         [0026]    When the controller operating the end effector unit  10  has determined that the unit is located within acceptable limits through operation of the micro positioner  45 , the end effector is deployed to machine an area of the workpiece. Ordinarily, the pressure foot plate  23  and spindle nose  13  are retracted during gross positioning of the end effector by a robot or other manipulating device. As previously indicated, the pressure bridge frame  19  and spindle nose  13  are extended or retracted by operation of the servomotor  31 . 
         [0027]    As suggested, applications of an end effector can benefit from or require a pressure foot that, through a spindle nose  13 , for example, first engages the work before a tool such as a drill bit is deployed. Moreover, it can be desirable to automatically remove a spindle nose or other extension of a pressure foot from an end effector when its function is not required, when automatic tool changeover requires removal of the spindle nose, and/or when a different spindle nose is needed. 
         [0028]    An automatic tool changer  51  of special construction disposed between the spindle nose  13  and the pressure foot plate  23  enables these operations to be performed automatically.  FIG. 5  illustrates a master side  52  and a tool side  53  of the tool changer  51  spread apart to show certain details of these components. Each side  52 ,  53  is a generally flat plate with a triangular outer profile and a large central bore  56 , the latter preferably being sufficiently large to fit around the spindle and housing  46 . A plurality of three ball locks  54  are fixed on an outer radial face of the master side  52  symmetrically disposed around the bore  56 . Each ball lock  54 , as shown schematically in cross-section in  FIG. 6 , has a cylindrical body carrying a set of radially movable balls  57 . The balls  57  are held in radially outward positions by air pressure introduced into a chamber  58  on an inner face of a piston  59  and are released when air pressure is introduced into the chamber  58  at an outer face of the piston  59 . The chambers  58  of the ball locks  54  on one side of their respective pistons  59  are interconnected, and on opposite sides of the respective pistons are similarly interconnected. Pressurized air is admitted to one or the other sides of the pistons  59  under the control of the end effector unit controller. It will be seen that when the pistons  59  are moved outwardly, the balls  57  are cammed and held radially outwardly. In their radially outward positions, the balls  57  are received in internal grooves  61  in bores  62  that receive the cylindrical ball lock bodies  54 . When the balls  57  are extended into the internal grooves  61  in the tool side  53 , the master and tool sides  52 ,  53  are locked together. The master and tool sides  52 ,  53  when initially being joined, are mutually aligned by two pins  63  projecting axially from a face of the master side  52 . The pins  63  are received in complementary holes  64  in the tool side  53 . Male and female brackets  66  on the periphery of the sides  52 ,  53  couple the vacuum tube  21  to the spindle nose  13 . The spindle nose  13  is rigidly bolted to the tool side  53  and the master side is rigidly bolted to the pressure foot plate  23 . The large bore  56  of the master and tool sides  52 ,  53  enables the lead end of the end effector unit spindle housing  46  to extend through it. This enables the housing  46  to be positioned as close as practical to the workpiece so that the spindle  12  and the quill (like that shown in  FIG. 9 ) are supported with a minimum cantilever effect even when the quill is extended. 
         [0029]      FIGS. 7-9  illustrate another end effector unit  70 ; parts that are identical or have substantially the same function to those shown in the embodiment of  FIGS. 1-6  are identified with the same numeral. A bolster plate  71  is fixed to the spindle housing  46 . Three cantilevered, axially oriented guide rods  72  extend rigidly from the front face of the bolster plate  71 .  FIG. 8  diagrammatically illustrates the location of these guide rods  72  relative to the spindle axis  15 . A pressure foot plate  73  has linear bearing units  74  that receive the guide rods  72  and enable the plate  73  to translate in the axial direction away from and towards the bolster plate  71 . Bolted to the pressure foot plate  73  is a transducer or load cell assembly  76  which comprises an adapter plate  75  carrying a load cell plate  77 . Three load cells  79 , equally spaced angularly and radially about the axis  15 , are mounted on the load cell plate  77 . A pressure plate  78 , a part of the load cell assembly  76 , bears against the load cells  79 . The master side  52  of a tool changer  24  is bolted to the forward side of the pressure plate  78 . The tool side  53  of the tool changer  24  carries a spindle nose  13 . 
         [0030]    It will be understood that the plates  73 ,  75 ,  77  and  78  each have a bore sized to slip over the quill end of the housing  46 . The load cells  79  are force transducers of, for example, of the Hall Effect type and measure axial force applied by the spindle nose  13 . A servomotor  31 , under control of the end effector controller, rotating a ball shaft in a ball nut  33  moves the spindle nose  13  against a workpiece or retracts the spindle nose. It will be understood that the end effector unit  70 , like the end effector  10 , is supported in an operating position on the end of a robot arm or other manipulating device. At the rear of the end effector unit  70 , a tool side  11  of an automatic tool changer is fixed to the unit. While not shown, a tool changer tool side for mounting either end effector units  10  or  70  can be fixed to a side of the unit where the geometry of the workpiece relative to the manipulating device is benefited. 
         [0031]    The array of load cells  79  detects the normality or perpendicularity of the spindle axis  15  to the surface of the workpiece by differential force or displacement readings. When the servomotor  31  presses the spindle nose  13  against the workpiece, one or two of the load cells  79  will be compressed to a greater degree than two or one of the other load cells where normality is absent. The load cell or load cells on the acute side of the angle made between the spindle axis  15  and a plane tangent to a workpiece surface will experience greater compression. The load cell signals are relayed to the robot or other machine controller ordinarily through connectors at the rear tool changer  11  to enable the controller to reposition the end effector  70  through robot movement so that the spindle axis  15  is more nearly perpendicular to the workpiece surface to be machined. 
         [0032]      FIG. 9  is a longitudinal cross-sectional view of the end effector unit  70 . The quill  81  is driven axially forward or rearward by a ball nut  82  threaded on a ball screw  83 . The ball screw  83  is rotated by the servomotor  16  ( FIG. 7 ) through a sheave  84  and belt  86 . A spindle assembly  87  carrying an automatic tool clamp  88  is rotated by a drive shaft  89 . The drive shaft  89  is driven by the servomotor  18  ( FIG. 7 ) through a belt  91  and sheave  92 . An external spline  93  on the drive shaft  89  mates with an internal spline  94  of the spindle assembly  87  to accommodate axial movement of the spindle assembly with the quill  81  relative to the drive shaft  89 . The automatic tool clamp  88  can be a commercially available unit such as manufactured by HSK. The tool clamp  89  is biased to a closed position by spring packs  95 ,  96  ( FIG. 9B ) operating on a draw bar  97  running along the axis  15 . As explained more fully in aforementioned U.S. Pat. No. 7,547,169, the automatic tool clamp  88  is opened or released when the quill  81  is fully withdrawn into the housing  46  and the forward end of the drive shaft  89  compresses the spring packs  95 ,  96 . The rear end of the draw bar  97  is received in a counterbore  90  in the forward end of the drive shaft  89 . Both the drive shaft  89  and draw bar  97  have central axially extending bores  98 ,  99  that communicate with one another. Extension and retraction of the quill  81  causes the rear or tail end of the draw bar  97  to telescope out of or into the forward end of the drive shaft  89 . 
         [0033]    Referring to  FIG. 9A , the rear end of the drive shaft  89  is fitted with a rotating union  101 . The rotating union may be a commercially available unit such as manufactured by Deublin Company headquartered in Waukegan, Ill. USA. Coolant or air can be admitted into a chamber  102  behind the stationary part of the rotating union to supply coolant through the drive shaft and draw bar bores  98 ,  99  to the automatic tool clamp  88  and ultimately to the drill or tool held in the tool clamp. A chamber  103  drains coolant which may return from the bores  98 ,  99  when the unit  70  is idling or otherwise inactive. A series of O-ring seals  104  are disposed in the counterbore  90  in the forward end of the drive shaft  89  for sealing on the exterior of the draw bar  97  to contain the coolant in the bores  98 ,  99 . 
         [0034]    While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described or in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.