Abstract:
In a preferred embodiment, a linear/rotary motor, including: a housing; an output shaft extending from the housing; a rotary motor disposed within the housing, the output shaft being given rotational motion by the rotary motor; a linear motor disposed within the housing; a linear shaft axially moveable by the linear motor; and a coupling to join the linear shaft and the output shaft to permit transfer of axial motion from the linear shaft to the output shaft but to isolate rotational motion of the output shaft from the linear shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of co-pending application Ser. No. 08/247,891, filed May 23, 1994, and titled LINEAR/ROTARY MOTOR. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates to electric motors generally and, more particularly, but not by way of limitation, to a novel electric motor which provides both linear and rotary motion at a single output shaft. 
     2. Background Art. 
     In certain applications, it is desirable to have a shaft which may selectively rotate and/or reciprocate. Such an application, for example, is in the robotic picking and placing of components where it may be required to axially move a component to an insertion position and then rotate the component to screw it in place. Conventional motor arrangements are often complicated and heavy, a substantial disadvantage for robotics applications. Another type of application requiring a shaft which may selectively rotate and/or reciprocate is in the precise control of laparoscopic and other such medical instruments. 
     In either type of application, it is frequently required that the linear motion be locked while rotary motion takes place. For a rotary/linear motor, this makes it desirable that the linear and rotary motions be controllable independently of one another. 
     A problem with motors having linear motion is that the motors frequently provide inadequate output shaft support when heavy side loads are imposed on the output shafts thereof. 
     Accordingly, it is a principal object of the present invention to provide an electric motor which provides both linear and rotary motion at a single output shaft. 
     It is an additional object of the invention to provide such an electric motor in which linear and rotary motions are controllable independently of one another. 
     It is another object of the invention to provide such an electric motor in which linear motion can be locked while rotary motion is provided. 
     It is a further object of the invention to provide such a motor that is simple and economical to manufacture. 
     An additional object of the invention is to provide such a motor that is lightweight and compact. 
     Another object of the invention is to provide a linear-type motor that has sufficient structure to support heavy side loads on the output shafts thereof. 
     Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a linear/rotary motor, comprising: a housing; an output shaft extending from said housing; a rotary motor disposed within said housing, said output shaft being given rotational motion by said rotary motor; a linear motor disposed within said housing; a linear shaft axially moveable by said linear motor; and coupling means to join said linear shaft and said output shaft to permit transfer of axial motion from said linear shaft to said output shaft but to isolate rotational motion of said output shaft from said linear shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figures, submitted for purposes of illustration only and not intended to define the scope of the invention, and on which: 
     FIG. 1 is is a side elevational view, partially in cross-section and partially cut-away, of one embodiment of a linear/rotary motor constructed according to the present invention. 
     FIG. 2 is an isometric view of a manufacturing operation employing a robotic operator with the linear/rotary motor of FIG.  1 . 
     FIG. 3 is a side elevational view, partially in cross-section and partially cut-away, of another embodiment of a linear/rotary motor constructed according to the present invention. 
     FIG. 4 is a side elevational view, partially in cross-section, of one embodiment of an end structure for supporting heavy side loads on the output shaft of a linear-type motor. 
     FIG. 5 is a side elevational view, partially in cross-section, of another embodiment of an end structure for supporting heavy side loads on the output shaft of a linear-type motor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference should now be made to the drawing figures, on which similar or identical elements are given consistent identifying numerals throughout the various figures, and on which parenthetical references to figure numbers direct the reader to the view(s) on which the element(s) being described is (are) best seen, although the element(s) may be seen also on other views. 
     Referring now to FIG. 1, there is illustrated one embodiment of a linear/rotary electric motor, generally indicated by the reference numeral  10 , and constructed according to the present invention. 
     Motor  10  includes a generally hollow housing  12  having end plates  14  and  16  fixedly attached at either end thereof. An output shaft  20  extends from end plate  16  and may move axially, as indicated by the arrow “A”, or the output shaft may rotate in either or both directions of rotation, as indicated by the arrow “B”. 
     Disposed interiorly of housing  12  is a linear motor  30  which is fixedly attached to end plate  14  and a rotary motor  32  which is fixedly attached to end plate  16 . Linear motor  30  has a splined shaft  34  extending therefrom and axially moveable within housing  12 , as indicated by the arrow “C”. Splined shaft  34  is integral with a threaded shaft  36  which passes through a threaded bore  37  axially defined internally through rotor  38  of linear motor  30 , such that rotary motion of the rotor causes shaft  36  to move axially within the linear motor and, thus, causes shaft  34  to move axially within the housing. 
     The distal end of shaft  34  is fixedly attached to an inner bearing member  40  of a shaft coupling, the latter generally indicated by the reference numeral  42 . Inner bearing member  40  is disposed within an outer bearing member  44 , the inner and outer bearing members being constructed of suitable bearing materials and being arranged for relative rotational motion therebetween. Inner bearing member  40  is held within outer bearing member  44  by means of a snap ring  46 . 
     Output shaft  20  is also the shaft for rotary motor  32  and rotates as the rotor  50  of the rotary motor rotates, as indicated by the arrow “B”. The proximal end of shaft  20  is fixedly attached to outer bearing member  44 . Shaft  20  is splined and passes through a central bore  52  defined through rotor  50 , the bore having a configuration complementary to the spline of shaft  20 . So configured, shaft  20  will rotate as rotor  50  rotates, but the shaft can freely move axially within the rotor. 
     In operation, output shaft  20  is given axial motion by linear motor  30  axially driving shaft  34 , with the axial motion thereof transferred through shaft coupling  42  by the axial motion thereof to shaft  20 . The axial motion of shaft  20  is unaffected by any rotary output of rotary motor  32 . Any such rotary output of rotary motor  32  is isolated from shaft  34  and linear motor  30  by means of shaft coupling  42 . The isolation of rotary motion from linear motor  30  is critical when the linear motor is of the lead screw type. 
     Linear motor  30  and rotary motor  32  may be any conventional types of such motors and the rotary motor may be a stepper motor such as furnished by Haydon Switch and Instrument, Inc., of Waterbury, Conn. 
     It can be seen that motor  10  is compact, relatively lightweight, and very simply and economically constructed. 
     An important feature of motor  10  is that linear motor  30  may be locked to prevent axial motion of output shaft  20  while the output shaft is being rotated by rotary motor  32 . Such locking may be accomplished in one of two ways. First, if the pitch of the threads on shaft  34  is relatively fine, say, 0.024″ or finer, simply de-energizing the stator coils of linear motor  30  will result in locking of that shaft (and output shaft  20 ) and axial force applied to the output shaft will not cause the shafts to backdrive. On the other hand, if the pitch of shaft  34  is relatively coarse, say, 0.048″ or coarser, axial force applied to shaft  34  will cause the shaft to backdrive. In the latter case, energization of both stator coils in motor  30  will electromagnetically lock up the motor rotor and lock shaft  34  (and output shaft  20 ) in place to resist axial movement of the output shaft. 
     In like manner, the coils of motor  32  can be energized so as to lock rotary motion of output shaft  20 . 
     FIG. 2 illustrates a manufacturing operation employing motor  10  and illustrating the use of linear locking. Elements common to those shown on FIG. 1 are given like reference numerals. Here, motor  10  is mounted vertically at the distal end of a robotic arm or other supporting structure  100 . A horizontal arm  102  is fixedly attached to the distal end of shaft  20  and an electromagnet  104  is fixedly mounted to the distal end of the horizontal arm. Electromagnet  104  is shown (solid lines) at a first elevation in position to pick up a part, as at  110 , from the surface of an incoming conveyor belt  112 . It may be assumed that output shaft  20  has been moved axially to the first elevation, shaft  34  (and the output shaft) locked, and shaft  20  rotated to the pickup position (solid lines). After electromagnet  104  picks up part  110 , linear motor  30  (FIG. 1) is energized to raise arm  102  to a second elevation and shaft  20  is linearly locked and then rotated clockwise by rotary motor  32  (FIG. 1) to place part  110  on a first workstation  120 . After a manufacturing operation takes place at first workstation  120 , part  110  is similarly raised to a third elevation and moved clockwise to a second workstation  122 . After completion of the manufacturing operation at second workstation  122 , arm  102  is rotated slightly clockwise, lowered to a fourth elevation, and rotated clockwise so that part  110  may be placed on the surface of an outgoing conveyor  130 . 
     FIG. 3 illustrates another embodiment of a linear/rotary motor, generally indicated by the reference numeral  200 , and constructed according to the present invention. As will be seen, motor  200 , although somewhat more complicated than motor  10  (FIG.  1 ), requires less total axial space for a given amount of linear motion. 
     Motor  200  includes a cylindrical, central shell portion  210  disposed between flanges  212  and  214 , the flanges being attached to a base plate  216  by suitable fastening means (not shown). Disposed at either end of motor  200  are linear and rotary motors  230  and  232 , respectively, having the same general functions as motors  30  and  32  of motor  10  (FIG.  1 ). In this case, however, motor  230  is of the type having the proximal end of a lead screw shaft  240  bonded to an aluminum rotor hub  242 , rather than being axially moveable within the rotor hub. A hexagonal, rotary output shaft  250  extends from an end of motor  200  and passes through a complementarily shaped axial bore  252  defined centrally of a rotor hub  254  in rotary motor  232 . 
     A shaft coupling, generally indicated by the reference numeral  260 , joins the proximal ends of lead screw  240  and output shaft  250 , the shaft coupling having an inner member  262  threadedly joined to the proximal end of the output shaft and an outer member  264  joined to a nut follower  266  by means of an anti-rotation pin  268 . Nut follower  266  engages lead screw  240  such that rotation of the lead screw causes axial back-and-forth motion of shaft coupling  260  and, therefore, the proximal end of output shaft  250 . The head of anti-rotation pin  268  engages and moves back-and-forth in an axial channel  270  defined in the inner surface of shell  210  to prevent the rotation of shaft coupling  260 . Thus, shaft coupling  260  isolates the linear and rotary functions of motor  200 , similar to purpose of shaft coupling  46  (FIG. 1) of motor  10 . 
     One feature of motor  200  which contributes to the compactness thereof is that the proximal end of lead screw  240  moves axially telescopingly within an axial bore defined centrally of the proximal end of output shaft  250  as the output shaft moves axially back and forth. A bronze bushing fixedly attached to the distal end of lead screw  240  provides support therefor within output shaft  250 . Another feature of motor  200  which contributes to the compactness thereof is that, because of the use of fixed lead screw  240 , motor  230  does not require any external support for lead screw  240 , in contrast to the external support extending from motor  30  (FIG. 1) of motor  10  to support axially moveable splined shaft  34 . 
     Motor  200  may be employed in the same manner as motor  10 , as described above with reference to FIG.  2 . 
     FIG. 4 illustrates one embodiment of a shaft support structure, generally indicated by the reference numeral  300 , useful for supporting a linear or linear/rotary motor shaft (neither type shown) when the shaft is used in an environment in which it will experience heavy side loads such as might be imposed by horizontal arm  102  (FIG.  2 ). 
     Structure  300  includes a housing  302  having first and second ends  304  and  306 , respectively. Structure  300  also includes a plurality of channels, as at  310  defined axially therethrough, to accept therein fasteners (not shown) for the attachment of first end  304  of the structure to, for example, end plate  16  of motor  10  (FIG.  1 ). 
     Disposed interiorly of structure  300  and near second end  306  are two, spaced apart ball bearing members  320  and  322  having sandwiched therebetween an insert  324 . Insert  324  is preferably formed form Delrin or a suitable metallic material having good lubricity. Ball bearing members  320  and  322  and insert  324  are secured in place by means of a snap ring (not shown) inserted in a counterbore  32 . 
     When structure  300  is assembled to motor  10  (FIG. 1) as described above, splined shaft  20  will extend through center bore  340  of insert  324 , the center bore having a configuration complementary to that of the splined shaft. Thus, any rotary motion of shaft  20  will be transmitted to ball bearing members  320  and  322  by insert  324 , while any linear motion of shaft  20  will cause the axial sliding of the shaft on the center bore  340  of the insert. Since ball bearings  320  and  322  and insert  324  are disposed well away from first end  204  of structure  300  which is mounted to end plate  16  (FIG.  1 ), shaft  20  is given good support against deflection by heavy side loads and shaft runout is reduced. 
     FIG. 5 illustrates another embodiment of a shaft support structure, generally indicated by the reference numeral  400 , also useful for supporting shafts with heavy side loads. 
     Structure  400  includes a housing  402  having first and second ends  404  and  406 , respectively. A mounting flange  410  formed at first end  404  has a plurality of holes defined therethrough for the attachment by fasteners (not shown) of structure  400  to end plate  16  of motor  10  (Figure). 
     Disposed approximately medially between first and second ends  404  and  406  is a first rotary/linear recirculating ball bearing member  420  and disposed near the second end is a second rotary/linear recirculating ball bearing member  422 , the first and second ball bearing members being coaxially aligned centrally of housing  402 . First bearing member  420  is secured in place by means of a snap ring (not shown) inserted in a counterbore  424  and second bearing member  422  is secured in placed by means of a snap ring (not shown) inserted in a counterbore  426 . 
     A cylindrical secondary output shaft  430  is supported by and extends through first and second bearing members  420  and  422  and has its distal end extending from second end  406  of structure  400 . 
     The distal end of secondary output shaft  430  terminates in a threaded portion  440  for the attachment thereto of a fixture, for example. The proximal end of secondary output shaft  430  is attached to an optional flexible coupling  450  for joining to shaft  20  of motor  10  (FIG.  1 ), for example, or the shaft of another motor. Alternatively, if radial motion does not have to be accommodated, secondary output shaft  430  may be an extension of output shaft  20 . As was the case with structure  300  (FIG.  4 ), bearings  420  and  422  are disposed well away from first end  204  of structure  400  which is mounted to end plate  16  (FIG.  1 ), and shaft  20  is, thusly, given good support against deflection by heavy side loads and runout is reduced. 
     It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.