Patent Publication Number: US-2012043832-A1

Title: Compact linear actuator with rotary mechanism

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of linear actuators. More particularly, the present invention is directed in one exemplary aspect to compact linear actuators having a rotary mechanism. 
     BACKGROUND OF THE INVENTION 
     Linear actuators are mechanical devices which are used to perform repetitive actions requiring linear motion. For example, linear actuators can be used in an assembly plant for placing caps on bottles, for automatically stamping or labeling mail, for glass cutting, for placing chips on circuits, for testing various buttons or touch areas on electronic devices, for automation, and for a wide variety of other purposes as well. 
     In certain applications, both linear and rotational motion are necessary to complete a designated task (for example, tightening screws and other such fasteners, laser welding, surface scanning or surface treatment application, light deflection using rotatable mirrors, etc.). In order to accomplish such rotation, a rotary motor can be affixed to the piston assembly of the actuator. However, this causes the linear motion of the actuator to become significantly slower since now the actuator must bear the mass of the rotary motor. 
     Therefore, a need exists for a linear actuator which can perform tasks requiring rotation, but without suffering an attendant loss in linear operational speed, force, and/or acceleration. Such an actuator should be compact, flexible, and yet still possess the ability to monitor and/or control the task being performed. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are therefore directed to a linear rotary actuator which satisfies each of the foregoing needs. More specifically, various embodiments of the present invention are directed to a linear rotary actuator with increased operational performance, the ability to transmit positional feedback (i.e., both linear and rotational data) to a remote device, as well as the ability to receive positional data specifying the amount of linear and rotational movement necessary for performing a particular task. 
     In a first aspect of the invention, a linear rotary actuator is disclosed. In one embodiment, the linear rotary actuator includes: a piston assembly comprising a rotatable shaft and a lock for engaging a pin adapted to prevent the piston assembly from rotating, wherein the shaft includes a groove for interfacing with a first bearing; the first bearing adapted to engage the shaft at the groove and therefore prevent the shaft from rotating relative to the first bearing; a second bearing comprising a magnet and adapted for being positioned around the first bearing; and a stator comprising a set of coils and adapted for being positioned around the second bearing, wherein the second bearing is adapted to rotatably engage the first bearing when current is flowing through the set of coils. 
     In a second aspect of the invention, a method is disclosed for rotatably engaging a first shaft disposed within the piston assembly of a linear actuator with a rotary motor that remains fixed irrespective of the linear position of the first shaft. In one embodiment, the method includes: positioning a stator comprising a set of coils around a rotary bearing comprising at least one magnet; positioning the rotary bearing around a first spline bearing adapted to receive the first shaft, wherein the rotary bearing is adapted to rotatably engage the first spline bearing, and wherein the first spline bearing is adapted to prevent rotation of the first shaft relative to the first spline bearing; inserting a second shaft into a rotational lock formed within the piston assembly; inserting the first shaft into the first spline bearing; and running an electrical current through the set of coils. 
     In a third aspect of the invention, an apparatus for performing a task requiring linear and rotational motion is disclosed. In one embodiment, the apparatus includes: a piston assembly comprising a lock adapted to prevent the piston assembly from rotating; a spline shaft connected to the piston assembly; a rotary motor comprising a stator and a rotor, wherein the rotor comprises at least one magnet, and wherein the stator comprises a set of coils and is positioned around the rotor; and a spline bearing positioned inside the rotor and adapted to interface with the spline shaft at a groove formed within the spline shaft. 
     These and other embodiments are described in more detail with reference to the following description and accompanying figures. Note that the following description and accompanying figures are merely exemplary in nature and should not be used to construe the invention as being limited to the specific embodiments described and illustrated herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a first exploded view of an exemplary linear actuator having a rotary motor according to one embodiment of the present invention. 
         FIG. 2  is a second exploded view of the exemplary linear actuator as depicted in  FIG. 1 . 
         FIG. 3A  is a first cut-away view of an exemplary linear actuator having a rotary motor according to one embodiment of the present invention. 
         FIG. 3B  is a second cut-away view of the exemplary linear actuator as depicted in  FIG. 3A . 
         FIG. 3C  is a third cut-away view of the exemplary linear actuator as depicted in  FIG. 3A . 
         FIG. 3D  is a fourth cut-away view of the exemplary linear actuator as depicted in  FIG. 3A . 
         FIG. 4  is a flow diagram of an exemplary method of rotatably engaging a shaft with a rotary motor that remains fixed irrespective of the linear position of the shaft according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1  and  FIG. 2  are exploded views of an exemplary linear actuator  100  having a rotary motor according to embodiments of the present invention. As shown by these figures, the linear actuator  100  includes a rotary motor housing  102 , a spline shaft  104 , a rotary encoder  106 , a coil  108 , a main housing  110 , a magnet housing  112 , a linear encoder  114 , an encoder housing  116 , a rotary bearing  118 , a rotational lock  120 , a rotary scale  122 , a linear scale  124 , a stator  126 , a bobbin  128 , a rotor  130 , a spline bearing  132 , and a piston assembly  134 . 
     In some embodiments, all or a portion of the manufactured parts can be machined on a CNC lathe such as the Hardinge model RS51MSY or other lathe that has the ability to machine both ends of a component (e.g., via sub-spindle transfer) as well as the ability to do mill work. According to some embodiments, each part can be made in a single operation on the lathe, thereby reducing and/or eliminating the need for secondary operations. These secondary operations present additional costs and may also reduce quality by increasing dimensional variation. 
     In some embodiments, various components of the linear actuator  100  may be manufactured from aluminum or steel bars. Note, however, that a myriad of other materials may be used according to embodiments of the present invention. 
     As best shown in  FIG. 2 , the piston assembly  134  may include at least one bobbin  128  for supporting an electrically conductive medium such as coil  108 . During operation, current is introduced through the coil  108  thereby creating a magnetic field having a direction that depends upon the direction that the current is flowing through the coil  108 . 
     In some embodiments, the piston assembly  134  and the bobbin  128  may be formed as a single, unitary piece. A single, unitary piece can make construction of the actuator  100  less complicated and quicker to assemble because there are fewer pieces. Moreover, using a single, unitary piece can be more cost effective, as a single piece can be less costly to produce than multiple separate pieces. A single, unitary piece can also weigh less than a multi-piece piston-bobbin assembly since such an assembly may require additional fasteners or hardware to attach the various components together. 
     The magnet housing  112  may include one or more magnets (for example, substantially cylindrical magnets or circular magnet segments) which may be easily fastened inside the magnet housing  112  during manufacturing with various adhesives or screws. Such magnets are adapted to magnetically interface with the piston assembly  134  when a magnetic field is present. Hence, by repeatedly alternating the direction that current is flowing through the coil  108 , a linear force may be repeatedly imparted upon the piston assembly  108 . 
     Note that while  FIG. 1  and  FIG. 2  each depict a single-coil actuator  100 , in other embodiments, the piston assembly  134  may include multiple coils  108  supported by separate bobbins  128  of the same piston assembly  134 , as well as a magnet housing  112  containing a series of alternately magnetized magnets (e.g., NS, SN, NS, etc.). Persons skilled in the art will recognize that the magnet housing  112  and piston assembly  134  for such a multi-pole configuration can be implemented using standard machining processes. 
     In some embodiments, stroke variation and encoder resolution may be easily adjusted, thereby reducing costs associated with reconfiguring and/or replacing the actuator. Where stroke is a function of three assemblies (the magnet housing  112 , the piston assembly  134 , and the main housing  110 ) a replaceable magnet housing  112  may be used to increase the length of the stroke, yet without requiring replacement of more expensive components that are serviceable in all stroke variations (e.g., the piston assembly  134  and the main housing  110 ). For example, the magnet housing  112  may be replaced with a more elongated magnet housing  112 , thereby enabling a longer actuator stroke. 
     As best shown in  FIG. 2 , the side of the piston assembly  134  opposite the coil  108  includes an interface for securing a spline shaft  104 . Such a spline shaft  104  may include, for example, a metallic shaft having one or more slits or grooves  105  (see, e.g.,  FIG. 3C ) running along its length. 
     One or more spline bearings  132  (e.g., annular bearings) having protrusions corresponding to the grooves  105  of the spline shaft  104  are adapted to receive the spline shaft and thereby prevent the shaft  104  from rotating relative to the spline bearings  132 . The spline bearings  132  may also serve to reduce the level of friction associated with linear movement of the shaft  104  relative to the spline bearings  132 . In order to accomplish this, the spline bearings  132  may include a set of balls, globules, or other such spherical bodies for circulating around a track within each respective bearing  132  as the shaft  104  is driven through each bearing  132 . In this manner, the spline bearings  132  may serve as a linear guide to the spline shaft  104  so as to prevent unwanted rotation of the shaft  104  and to further enable linear movement of the shaft  104  with a reduced amount of associated friction. In one embodiment, the spline bearing  132  may include a linear guide assembly manufactured by IKO Inc. (#MAG8CITHS2/N). Note, however, that a myriad of other structures/guide assemblies may be utilized according to the scope of the present invention. 
     In some embodiments, the central axis of the bobbin  128  supporting coil  108  is approximately collinear with the spline shaft  104 . This design can help reduce or eliminate an unwanted moment, or a lateral force which may otherwise translate to the piston assembly  134  if the coil were positioned to one side of the piston assembly  134 . Such a design can improve force repeatability which is particularly useful in precise force applications such as small electronic parts assembly and precision glass scoring. 
     In some embodiments, the piston assembly  134  may include a linear scale  124  for indicating linear positional feedback to a linear encoder  114 . As shown in  FIG. 1  and  FIG. 2 , the linear encoder  114  may be situated within an encoder housing  116  which is itself disposed within a cutout of the main housing  110 . The encoder housing  116  can be fastened to the main housing  110  of the actuator  100  using screws, for example. The linear encoder  114  may thus remain fixed within the main housing  110  as the piston assembly  134  is repeatedly actuated. 
     As best shown by  FIG. 3D , the linear scale  124  may include a series of stripes or markings running along the length of the scale. When the piston assembly  134  is actuated, the linear encoder  114  (e.g., an optical reader) may count the number of stripes or markings read in order to determine the current linear position of the piston assembly  134 . In some embodiments, recorded positional data may then be transmitted to a remote device for monitoring purposes. In some embodiments, a user can input one or more values to a remote device (such as a connected computer) in order to designate an amount of linear movement desired for a particular task. These values can then be transmitted to a controller (not shown) in electrical communication with the linear encoder  114  so that linear movement of the piston assembly can be adjusted according to the values specified. 
     In order to enable the linear actuator  100  to perform tasks requiring rotation, a rotational lock  120 , a rotary bearing  118 , and a rotary motor including stator  126  and rotor  130  may be utilized in conjunction with the various components mentioned above for enabling linear operation. These components are best described and illustrated with reference to the following figures. 
       FIGS. 3A-3D  are various cut-away views of an exemplary linear actuator having a rotary motor according to one embodiment of the present invention. According to the design of the embodiments depicted in these figures, the rotary motor remains fixed irrespective of the linear position of the shaft  104 , thereby enabling the shaft  104  to move in linear direction without being substantially encumbered by the mass of the rotary motor. A smaller force is thereby necessary to drive the linear actuator  100  at a designated acceleration. Similarly, a greater acceleration is attainable for a specified amount of force. 
     Referring first to  FIG. 3A , the first cut-away view depicts a spline shaft  104  with one or more grooves  105  running along its length, one or more spline bearings  132  for guiding the spline shaft  104  upon being actuated in a linear direction, a rotary scale  122  for indicating rotational feedback to a rotary encoder  106 , one or more rotary bearings  118  for enabling rotation of the shaft  104  relative to the piston assembly  134  (not shown), and a rotational lock  120  for preventing the piston assembly from rotating as the shaft  104  is rotated. 
     As discussed above with reference to  FIGS. 1 and 2 , the one or more spline bearings  132  are adapted to prevent the shaft  104  from rotating relative to the spline bearings  132 . Thus, when the spline bearings  132  remain fixed, movement of the shaft  104  is linearly guided by the spline bearings  132  along the grooves  104  of the spline shaft  104 , thereby preventing rotation. 
     However, even though the spline shaft  104  may not rotate relative to the spline bearings  132 , the spline shaft  104  and spline bearings  132  may rotate in tandem relative to the piston assembly  134  (not shown). One or more rotary bearings  118  positioned at the proximal end of the spline shaft  104  may be used to secure the shaft  104  to the piston assembly  134 , yet also enable the shaft  104  and spline bearings  132  to rotate relative to the piston assembly  134 . 
     The piston assembly  134  may include a rotational lock  120  for preventing the piston assembly  134  from rotating during operation. The rotational lock  120  may include one or more apertures for receiving a locking pin  136 , spline shaft, or other such locking mechanism while remains fixed while the shaft  104  is rotated. In some embodiments, the rotational lock  120  may be formed directly within the piston assembly  134 , thereby reducing the number of parts necessary for assembly of the linear actuator  100 . In some embodiments, the rotational lock  120  may include a spline bearing  132  for reducing the amount of friction between the rotational lock  120  and the locking pin  136  as the piston assembly  134  is actuated and the rotational lock  120  slides upon the spline shaft or locking pin  136 . 
     Optionally, the linear actuator  100  may include a rotary scale  122  for indicating rotational feedback to a rotary encoder  106 . As best shown in  FIG. 3A  and  FIG. 3B , the rotary scale  122  may include a series of stripes or markings oriented radially across the surface of the rotary scale  122 . When the spline bearings  132  are rotated, the rotary encoder  106  (e.g., an optical reader) may count the number of stripes or markings it has read in order to determine how far the spline shaft  104  has rotated. Rotational data recorded in this manner may then be transmitted to a remote device for monitoring purposes. 
     According to some embodiments, a user can input one or more parameters to a remote device (such as a connected computer) in order to designate an amount of rotational movement desired for a particular task. These values can then be transmitted to a controller (not shown) in electrical communication with the rotary encoder  106  so that rotational movement of the spline shaft  104  can be adjusted according to the values specified. 
     Referring next to  FIG. 3B , the shaft  104  of the actuator  100  is presented with one or more rotors  130  for rotatably engaging the spline bearings  134 . In some embodiments, the one or more rotors  130  include rotary bearings each containing at least one magnet (e.g., an annularly-shaped magnet). In some embodiments, the one or more rotors  130  are positioned around the spline bearings  134  such that rotation of a rotor  130  causes rotation of the spline bearings  132 , which in turn causes rotation of the shaft  104  of the actuator  100 . 
     Turning next to  FIG. 3C , the shaft  104  of the actuator  100  is now depicted with stators  126  for rotatably actuating the corresponding rotors  130 . Each stator  126  may include an electrically conductive medium, such as set of coils (not shown) for electric current to run through. The magnetic field generated when current running through the coils magnetically actuates the rotors  130 , thereby causing rotation of the spline bearings  134  and hence the shaft  104 . Thus, the shaft  104  of the actuator  100  can repeatedly rotate in clockwise and counter-clockwise directions by repeatedly switching the current flow to the coils of the stators  126 . 
       FIG. 3D  illustrates the shaft  104  of the actuator  100  as secured to the piston assembly  134  via the rotary bearings  118 . As shown in this figure, the piston assembly  134  includes a linear scale  124  for indicating the linear position of the piston assembly  134  to a linear encoder  114  (shown in  FIG. 1  and  FIG. 2 ). Since the linear actuator  100  can determine both the linear position of the piston assembly  134  (e.g., via the linear scale  124  and linear encoder  114 ) as well as the rotational of the shaft  104  (e.g., via the rotary scale  122  and the rotary encoder  106 ), positional data may be used to monitor the operation of the actuator  100 . In some embodiments, the linear encoder  114  and/or the rotary encoder  106  are adapted to control operation of the linear actuator  100  based upon one or more designated parameters. These parameters may include, without limitation, linear force, linear speed, linear position, linear acceleration, rotational force, rotational speed, rotational position, and rotational acceleration. 
       FIG. 4  is a flow diagram of an exemplary method of rotatably engaging a shaft with a rotary motor that remains fixed irrespective of the linear position of the shaft according to one embodiment of the present invention. 
     At block  402 , a stator may be positioned around a rotor (e.g., a rotary bearing). In some embodiments, both the stator and the rotor may be formed into an annular shape, where the stator includes a set of coils and is adapted to remain fixed, and where the rotor is adapted to rotate relative to the stator upon being magnetically actuated by a magnetic field generated when current is running through the set of coils. 
     At block  404 , the rotor is positioned around a spline bearing (e.g., a ball spline) so as to rotatably engage the spline bearing upon actuation from the magnetic field generated by the stator. In some embodiments, the rotor comprises an annular body having a central aperture adapted to fit around the periphery of the spline bearing. Thus, when the rotor is magnetically actuated by the stator (i.e., rotates), the spline bearing rotates in tandem. 
     At block  406 , the piston assembly of the actuator is locked. This may be accomplished, for example, by inserting a locking pin or external spline shaft into an aperture formed directly in the piston assembly or inside a rotational lock that is connected to the piston assembly. In some embodiments, the aperture is adapted to slide over the locking pin or external spline shaft as the piston assembly is repeatedly actuated. Optionally, the rotational lock may include a spline bearing for reducing a level of friction between the rotational lock and the external spline shaft as the piston assembly is actuated. 
     At block  408 , the shaft of the actuator is inserted into the spline bearing. In some embodiments, the spline shaft includes a set of one or more grooves running along its length. A set of protrusions formed on the inside surface of the spline bearing are adapted to interface with the set of one or more grooves of the spline shaft and thereby prevent the shaft from rotating relative to the spline bearing. 
     At block  410 , current is run through the coils of the stator. The magnetic field generated thus causes rotation of the rotor, the spline bearing, and hence, the shaft. Since the shaft of the actuator may be linearly actuated without bearing the mass of the rotary motor, operational performance of the actuator may be substantially improved. 
     Note that various actuators  100  described herein can be manufactured and assembled quickly and cost-effectively. Further, the actuators  100  may be manufactured to be relatively small, lightweight, and compact. Optionally, use of optical linear and rotary encoder assemblies  114  and  106  can provide monitoring and control over 100% of movement affected by the actuators  100 . Additionally, the individual design of the main housing  110 , the magnet housing  112 , and the piston assembly  134  can provide flexibility and easy reconfigurability so that various actuator configurations can conform to the specifications of a particular project. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example architectural or other configuration for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated example architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in some combination, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments.