Abstract:
An actuator includes an outer sleeve with at least a pair of helical slots coiling in a first direction, an inner sleeve with at least a pair of helical slots coiling in a second, opposite direction, and a driver including bearings received through the helical slots of the inner sleeve and into the helical slots of the outer sleeve.

Description:
FIELD OF THE INVENTION This invention relates to actuators which convert linear motion to rotational motion and vice versa. 
     BACKGROUND OF THE INVENTION 
       [0001]    There are many mechanical systems requiring the conversion of linear motion to rotational motion. In one example, a robot forearm may need to rotate using an actuator within an upper arm connected to a shoulder. Helical gears (See. U.S. Pat. No. 5,447,095) are heavy and complex. Some actuators have a limited range of motion. Other actuators occupy too much space. Some suffer from high friction. 
       SUMMARY OF THE INVENTION 
       [0002]    Aspects of the invention may provide for an actuator which is lightweight, involves few moving parts, and has a range of motion adaptable for numerous applications. The actuator has a form factor which is long and slender and may include rolling elements with low friction. In some examples, an actuator is provided with a range of motion greater than 360°. The actuator may be back drivable and can be used as a differential. in some aspects, the actuator can be designed with integral internal fluid routing using, for example, slip rings. 
         [0003]    Featured are counter-rotating helical cams in the form of inner and outer sleeves, each with at least a pair of helical slots therethrough. A driver includes bearing surfaces received through the helical slots of the inner and outer sleeves. 
         [0004]    Featured is an actuator comprising an outer sleeve with at least a pair of helical slots running in a first direction an inner sleeve with at least a pair of helical slots running in a second, opposite direction and a driver including bearings received through the helical slots of the inner sleeve and into the helical slots of the outer sleeve. 
         [0005]    The helical slots of the sleeves may wrap partially around or more. The helical slots of the inner and outer sleeve may have a constant but different pitch, or a non-constant and different pitch. There can be at least four helical slots in the outer sleeve and four helical slots in the inner sleeve. 
         [0006]    The driver may include a cross-member supporting the bearings thereon and a piston extending from the cross-member. In one design, there are a pair of roller bearings on each end of the cross-member, one inner roller bearing of each pair for a helical slot in the inner sleeve, one outer roller bearing of each pair for a helical slot in the outer sleeve. The bearings can be cylindrical bearings. If the slots are tapered, the bearings can be conical bearings. The driver may be hydraulically driven, electrically driven, or mechanically driven. 
         [0007]    The driver may include at least two cross members. 
         [0008]    The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0010]      FIG. 1  is a schematic view of a robot arm showing a use of the actuator of the subject invention in one particular example; 
           [0011]      FIG. 2  is a cross-sectional view of an example of an actuator in accordance with the invention; 
           [0012]      FIG. 3  is a schematic three dimensional front view of the actuator of  FIG. 2 ; 
           [0013]      FIG. 4  is a schematic three dimensional view of the actuator of  FIGS. 2-3 ; 
           [0014]      FIG. 5  is a schematic cross-sectional view of the actuator of  FIGS. 2-4 ; 
           [0015]      FIG. 6  is a schematic view showing an example of a tapered helical slot in a sleeve and a conical roller bearing in accordance with examples of the invention; 
           [0016]      FIG. 7  is a schematic three dimensional front view of the outer sleeve of the actuator; 
           [0017]      FIG. 8  is a schematic three dimensional front view of the inner sleeve of the actuator; 
           [0018]      FIG. 9  is a schematic three dimensional cross-sectional view of the coaxially nested actuator sleeves; 
           [0019]      FIG. 10  is a schematic three dimensional front view of another actuator in accordance with an example of the invention; 
           [0020]      FIG. 11  is a schematic three dimensional front view of the driver for the actuator of  FIG. 10 ; and 
           [0021]      FIG. 12  is a schematic three dimensional front view of another example of an actuator in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0023]      FIG. 1  shows a robot arm  10  with actuator  12  inside upper aim  14  and configured to rotate forearm  16 . This is but one use for actuator  12 . It may be used in a variety of systems where linear to rotary motion conversion is required (and vice versa). The actuator can also be used as a differential. In one specific example, piston shaft  11  is a component of a linear driver for actuator  12  and piston shaft  11  is hydraulically driven via hydraulic cylinder  18 . In other examples, the driver may be electrically driven or mechanically driven. A linear voice coil motor, for example, is possible. 
         [0024]      FIGS. 2-5  show actuator  12  comprising outer sleeve  20  and inner sleeve  22 . Outer sleeve  20  includes a pair of helical slots  24   a  and  24   b  through the wall of the sleeve. Inner sleeve  22  also includes a pair of helical slots  26   a  and  26   b  coiled in the opposite direction of the helical slots  24   a  and  24   b  in the outer sleeve. Driver  30  includes, in this example, cross-member  32  attached to piston shaft  11  and supporting outer roller journal bearings  34   a  and  34   b  riding in helical slots  24   a  and  24   b,  respectively, in outer sleeve  20  and inner roller bearings  36   a  and  36   b  riding in helical slots  26   a  and  26   b,  respectively, of inner sleeve  22 . In other designs, the bearing surfaces on the ends of the cross member can include rolling or sliding elements, journal bearings, and sliding shoes of different shapes. If inner sleeve  22  is fixed, linearly driving piston shaft  11  causes outer sleeve  20  to rotate. Conversely, if outer sleeve  20  is fixed, inner sleeve  22  will rotate as piston shaft  11  moves (up and down in the figures). 
         [0025]    The helical slots in each sleeve may wrap around their respective sleeves partially, once, or more. They may have a constant pitch as shown. The slots of the inner sleeve may have a different pitch than the slots of the outer sleeve. The helical slots of the outer and inner sleeve may also have a non-constant pitch and again the pitch of the helical slots in the outer sleeve is typically different than the pitch of the helical slots in the inner sleeve creating a non-linear transmission. 
         [0026]      FIG. 6  shows a design where helical slot  14   b ′ in outer sleeve  20  has a tapered profile and roller bearing  24   b ′ is conical in shape to match the tapered profile of the slot it rides in. The helix slots of both sleeves may be configured in this fashion and all the roller bearings may be conical in shape. 
         [0027]      FIG. 7  shows outer sleeves with helical sots  24   a  and  24   b.    FIG. 8  shows inner sleeve  22  with helical slots  26   a  and  26   b.    FIG. 9  shows both sleeves coaxially disposed in a nested fashion without the driver. 
         [0028]      FIG. 10  shows a design with a driver including two spaced offset cross members  32   a  and  32   b  for backlash reduction. The driver is also shown in  FIG. 11 . Here, the bearing surfaces on the ends of the cross members slide in their respective slots in the sleeves. 
         [0029]      FIG. 12  shows a design where outer sleeve  20 ′ includes four-start helix pattern (four helical slots) as does inner sleeve  22 ′. The driver may include two cross members or four. 
         [0030]    By integrating internal fluid routing and slip rings, hydraulic fluid can be provided downstream of the actuator, for example, to one or more components in forearm  16 ,  FIG. 1 . 
         [0031]    The resulting actuator in its various embodiments is lightweight, involves few moving parts, and has an adjustable range of motion suitable for numerous applications. The preferred actuator has a form factor which is long and slender and includes rolling elements with low friction. 
         [0032]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
         [0033]    In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
         [0034]    Other embodiments will occur to those skilled in the art and are within the following claims.