Abstract:
A compact integrated servo motor and gear reducer assembly that includes a rotor having a rotor shaft and a stator, and a planetary gear system including a sun gear, a plurality of planet gears and an outer ring gear. First and second bearings support the planetary gear system. The first and second bearings are located on opposing sides of the planetary gear system, and the first bearing has a first diameter and the second bearing has a second diameter. A third bearing supports the rotor shaft, and the third bearing has a third diameter that is less than the first and second diameters. Moreover, the third bearing is positioned between an edge of the first bearing and an edge of the second bearing. The assembly can be used in applications requiring high torque output but yet with size and/or space limitations.

Description:
FIELD OF THE INVENTION 
     The present invention is generally directed to electric servo actuators and, more particularly, to a compact electric servo actuator having an integrated servo motor and gearhead assembly. 
     BACKGROUND 
     Electric servo actuators have many functions and are found in a variety of industrial applications. They are used to control positions, velocities or torques applied to various machine components. Typical applications include machine tools, packaging equipment as well as web processing equipment. Electric servo actuators are selected based upon the design parameters for a particular application. The design parameters that influence the selection process include the torque, rotational speed and power requirements. With respect to electric servo actuator design, it is well known in the art that power is proportional to the product of torque times rotational speed. Using this basic design principle, design engineers can modify the output torque from a servo motor by decreasing the servo motor&#39;s output rotational speed. 
     In practice, gear reducers are often used to convert the high rotational speed of servo motors into a higher torque, lower rotational output speed. Many types of gear reducers are available. One type of gear reducer is a planetary style reducer. This particular style of reducer uses a planetary arrangement of gears to apply a reduction ratio that is in an in-line (concentric) configuration. Planetary gear reducers are generally characterized by their small size, robustness, quiet operation, and low backlash. In typical applications, planetary gear reducers are made in modular form and are mounted to a standard servo motor to achieve the required speed reduction. FIG. 1 illustrates a typical design configuration having a servo motor  15  operably connected to a gear reducer  16 . As shown in FIG. 1, adapter  17  is mounted to output shaft  18  of servo motor  15 . Similarly, pinion  19  attaches to adapter  17  opposite servo motor  15 . Gear reducer  16  receives as input pinion  19  and is selected to produce the desired output torque and rotational speed at shaft  20 . 
     Conventional design configurations such as those exemplified in FIG. 1 have several shortcomings. For example, in situations where space and size are of concern, the addition of the components necessary to couple the servo motor with the gear reducer severely limits design options. Conventional configurations address this concern by using right angle gearheads and motors. However, this approach requires additional components and hence leads to a more expensive and heavier system. 
     Moreover, the conventional approach requires service personnel to manually couple the gear reducer to the servo motor. Often, this process requires special and proprietary mounting methods to fasten the gear reducer to the servo motor. Additionally, the process can result in improper installation or misalignment of the gear reducer with respect to the servo motor&#39;s output shaft. For example, if the modular gear reducer is not fastened to the servo motor properly, the strength of the pinion-shaft joint is weakened and can result in premature failure of the components. 
     Accordingly, there arises a need to provide for an electric servo actuator having substantially the same performance characteristics as a conventional motor and gearhead configuration but with the added feature of being very compact in relation to the conventional approach. Such an electric servo actuator and gearhead configuration would provide greater flexibility with respect to size and space considerations and substantially reduce installation and maintenance costs. The present invention addresses and overcomes the shortcomings of the prior art. 
     SUMMARY 
     The present invention generally provides a compact integrated servo motor and gear reducer assembly maintained within a unitary housing. The compact integrated servo motor and gear reducer assembly can be used in applications requiring high torque output but yet with size and/or space limitations. The present servo motor and gear reducer assembly may, for example, also reduce installation and maintenance costs associated with the operation of servo motors and gear reducer assemblies. 
     In a preferred embodiment of the invention, a servo motor and gear reducer are provided within a unitary housing. The servo motor is supported within the unitary housing at its distal end with bearings near the rear of the unitary housing. At its proximal end, the servo motor is supported with bearings and its output shaft is operatively connected directly to the gear reducer. In a preferred embodiment of the present invention, the gear reducer is a planetary gear system. Hence, the servo motor&#39;s output is operatively connected directly to the sun gear of the planetary gear system. In one embodiment, the servo motor rotor and the sun gear may be constructed as a unitary piece (or with the sun gear pressed onto a shaft area of a unitary piece). Furthermore, the bearings supporting the servo motor at its proximal end are contained substantially within and concentric with the planetary gear system. As a result of this configuration, the axial length of the overall assembly is reduced. 
     In operation, the servo motor rotates the input shaft of the planetary gear reducer, specifically, the sun gear. The output from the planetary gear system is transferred to a planet carrier. The planet carrier has a unitary design and is fully supported with a pair of bearings. As used herein, the term “fully supported” includes large diameter bearings on both sides (e.g., axially) of the planet gears. At least one prior design placed two bearings on the output shaft side of the gear system. However, this leads to planet gears which are supported in a cantilevered fashion. The present invention overcomes this shortcoming by placing bearings on either side of the planet/sun gear system. Also, as noted above, the sun gear bearing is placed axially within the planet carrier bearings. 
     Another feature of the present invention is that the bearings supporting the servo motor at its distal end are located axially within and concentric with the servo motor&#39;s windings. This feature of the present invention further contributes to the compactness of the overall assembly design. 
     As discussed above, the present invention provides for a compact integrated servo motor and gear reducer assembly contained within a unitary housing. Hence, all of the moving components, including the servo motor, planetary gear system, and support bearings, are contained within the unitary housing. In a preferred embodiment of the present invention, input and output ports are provided to allow for lubrication. As a result of this design, the moving parts of the of the present invention can be lubricated with a simple low pressure oil circulation system. Therefore, the integrated servo motor and gear reducer assembly of the present invention is capable of operating at increased power levels as compared to conventional servo motor and gear reducer assemblies. 
     Each of the identified features contribute toward a goal of optimizing the power density of the motor in view of cross-sectional constraints. This allows for embodiments, which are constructed in accordance with the principles of the present invention, offering a short axial length given power and diameter requirements. 
     Therefore, according to one aspect of the invention, there is provided an integrated rotary servo actuator apparatus, comprising: a rotor, having an output shaft; a stator; a planetary gear system, including a sun gear, a plurality of planet gears and an outer ring gear, wherein the sun gear is directly connected to said output shaft and a load shaft is connected to said planet gears; first and second bearings for supporting said planetary gear system, said first and second bearings located on opposing sides of said planetary gear system; and a third bearing for supporting said output shaft, wherein said third bearing is arranged and configured to be axially aligned within the area defined by and between said first and second bearings. 
     According to another aspect of the invention, there is provided a rotary servo actuator as recited in the preceding paragraph, wherein said stator includes a plurality of windings; and further comprising: a fourth bearing to support said rotor; said fourth bearing being arranged and configured to be axially aligned within said windings. 
     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which like parts are identified by like reference numerals. 
     FIG. 1 illustrates a conventional configuration for prior art electric servo motors; 
     FIG. 2 is a perspective view of an integrated rotary servo actuator  50  constructed in accordance with the principles of the present invention; 
     FIG. 3 a  is an exploded view of the four main sub assemblies of the integrated rotary servo actuator  50  of FIG. 2; 
     FIG. 3 b  is an exploded view of the four main sub assemblies of the integrated rotary servo actuator  50  of FIG. 2 with the rotor assembly  52  located in its operative position within the stator assembly  53 ; 
     FIG. 4 is a schematic cross-sectional view of the exemplary integrated servo motor and gear head assembly  50  of FIG. 2; 
     FIG. 5 is an elevated side view of the integrated rotary servo actuator  50  of FIG. 2; 
     FIG. 6 a  is a cross section view of the integrated rotary servo actuator  50  of FIG. 5 taken through line  6   a - 6   a;    
     FIG. 6 b  is a cross section view of the integrated rotary servo actuator  50  of FIG. 5 taken through line  6   b - 6   b;    
     FIG. 6 c  is a cross section view of the integrated rotary servo actuator  50  of FIG. 5 taken through line  6   c - 6   c;    
     FIG. 7 is an exploded view of the gearhead assembly  51  of the integrated rotary servo actuator of FIG. 2, with the sun and planet gears assembled; 
     FIG. 8 is an exploded view of the gearhead assembly  51  of FIG. 7 with the sun and planet gears exploded; 
     FIG. 9 is a perspective view of the planet gear carrier  120 ; 
     FIG. 10 is a perspective view of a partially exploded gearhead assembly  51  taken from the rear and left-side; 
     FIG. 11 is a partially exploded view of the feedback assembly housing  54  of the integrated rotary servo actuator of FIG. 2; 
     FIG. 12 is a schematic cross sectional view of an alternative embodiment integrated rotary servo actuator; 
     FIG. 12 a  is a schematic cross sectional view of an alternative embodiment integrated rotary servo actuator; 
     FIG. 12 b  is a partially exploded view of the actuator of FIG. 12 a;    
     FIG. 13 is a schematic cross sectional view of a second alternative embodiment integrated rotary servo actuator; and 
     FIG. 14 illustrates the integrated rotary servo actuator in a representative environment in which a device constructed in accordance with the present invention might be employed. 
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The present invention is generally directed to electric servo actuators and in particular is directed to an electric servo actuator having an integrated servo motor and gear head assembly. While the present invention is not so limited, a more detailed understanding of the present invention will be gained through a discussion of the drawings in connection with the examples provided below. 
     Referring first to FIG. 2, a perspective view of a preferred integrated servo motor and gear head assembly (or integrated rotary servo actuator) constructed in accordance with the principles of the present invention is shown. The integrated rotary servo actuator  50  is generally designated at  50 . For convenience, the integrated rotary servo actuator  50  may be referred to herein as actuator  50 . 
     Still referring to FIG. 2, actuator  50  includes a keyed output shaft  101  for providing power to the load (best seen in FIG. 14 at  102 ). As noted above, the load may be comprised of any number of various machine components. Through holes  103  are provided through front end plate  104  for mounting the actuator  50  in a working environment in a known manner. Three external housing components  105 ,  106  and  107  fit in a sealing engagement and house the gearhead assembly  51 , motor stator  53 , and feedback assembly  54 , respectively, in a unitary housing. Back end plate  108  fits in sealing engagement with external housing component  107 . Also visible in FIG. 2 is cooling oil port  109 , feedback connector  110  and power connector  111 . 
     Next referring to FIGS. 3 a  and  3   b , the four main sub-assemblies of the actuator  50  are shown in a partially exploded form. The four sub-assemblies are the gearhead assembly  51 , the motor rotor assembly  52 , the motor stator assembly  53  and the feedback assembly  54 . FIG. 3 a  illustrates the motor rotor assembly  52  out of its working position within the motor stator assembly  53 , while FIG. 3 b  illustrates the motor rotor assembly within its working position (e.g., located within the stator). 
     FIG. 4 illustrates a schematic cross-sectional view of an integrated servo motor and gear head assembly  50  in accordance with the present invention. The integrated servo motor and gear head assembly  50  is fully contained within a single housing made up of the front end plate  104 , gearhead housing  105 , motor stator housing  106 , feedback housing  107  and rear end plate  108 . Located within the single housing are the four main subassemblies identified above. 
     Comprising the servo motor means (or prime mover) of the present invention are the motor stator assembly  53  and the motor rotor assembly  52 . The motor means includes windings  112  and a rotor  113 . In a preferred embodiment of the present invention, the motor means is a brushless permanent magnet motor optimized for compactness. Furthermore, the servo motor means can be selected to yield the highest possible power density available. For example, the servo motor means could use rare earth permanent magnets made of neodinium iron boron and wound with maximum slot fill. In a preferred embodiment of the present invention, only two bearings are used to support servo motor rotor  113 . Servo motor rotor  113  is supported in the rear by rear motor bearing  114 . Similarly, servo motor rotor  113  is supported at the front by front motor bearing  115 . Rear shaft  131  is used for connecting an encoder (or other feedback device for closed loop operation of the actuator in combination with the controller block  124 —best seen in FIG.  14 ). 
     The planetary gear assembly  51  is operatively connected to the servo motor rotor assembly  52  at its proximal end. Specifically, sun gear  116  is directly connected to rotor shaft  117 , which is also connected to the servo motor rotor  113 . Shaft  117  is a tapering shaft which can be inserted within the rotor motor  113  (best seen in FIGS. 12 a  and  12   b ). Tapering shaft  117  is self-locking. Bolt  118  secures sun gear  116  within servo motor rotor  113 . 
     Since the sun gear and the motor rotor are constructed from the same material, selection of the material from which the components are constructed is important. For example, the materials must provide a high quality, high strength gear, and also needs to provide good magnetic properties to provide a proper magnetic field under the motor magnets. In the present case, an alloy of stainless steel has demonstrated the required characteristics. Preferably the stainless steel is 17-4 Ph. 
     In addition to supporting motor rotor  113 , front motor bearing  115  also supports sun gear shaft  117  (this bearing may also be referred to as the sun gear bearing herein). Thus, front motor bearing  115  serves as an accurate means of locating planet carrier  119  by fixing the center of location of sun gear  116  within the planetary gear system  120  (best seen in FIGS. 6 a ,  8 , and  9 ). Furthermore, this reduces the loss of power transmission from servo motor means to the planetary gear system  51  and increases the bearing life of front motor bearing  115 . 
     More specifically, the bearing life of the front motor bearing  115  is increased since the outer race is not fixed, but rotates with the planet carrier. Since the planet carrier rotates the same direction as the motor rotor shaft, the relative rotational speed of this bearing is less than if it was mounted in a bulkhead or faceplate of a conventional motor. Because it is rotating slower, it has a longer life. 
     To further reduce the size of the integrated servo motor and gear head assembly  50  in the axial direction, servo motor stator windings  112  are configured such that rear motor bearing  114  supports the motor rotor  113  within the stator windings  112  as shown in FIG.  4 . In other words, the bearing  114  is positioned between a front edge E 3  of the stator windings  112  and a rear edge E 4  of the windings  112 . In a conventional motor, the rear motor bearing support is axially positioned beyond (or rearward of) the point where the stator windings are located. However, in a preferred embodiment of the present invention, the diameter of rotor motor  113  is purposely increased. Likewise, the inside diameter of stator windings  112  is also increased. In so doing, adequate radial space is present within stator windings  112  to receive rear motor bearing  114  and support motor rotor  113 . This configuration can significantly reduce the axial length of the overall assembly. For example, in the case of a NEMA size 34 device, this saves approximately ½″ of length, or approximately 5-10% of the overall length of the entire configuration. 
     Planet carrier assembly  51  has a fully supported design. As noted above, preferred embodiments constructed in accordance with the principles of the present invention are fully supported with large diameter bearings  121  and  122  on both sides (e.g., axially) of the planet gears  123 . Further, the sun gear bearing  115  is arranged and configured to lie axially within the fully supported planet carrier. In other words, the bearing  115  is positioned between an rear edge E 1  of the bearing  121  and a front edge E 2  of the dearing  122 . By locating the planet carrier in this manner, the carrier has the responsibility of providing the bearing alignment accuracy for a total of three bearings (e.g., the two planet carrier bearings  121 ,  122  and the sun gear bearing  115 ). This leads to a high accuracy gear head since a single component aligns all three bearings. Possible misalignment of that component to the planet carrier is possible in other designs because other gear heads use a separate component to mount the sun gear bearing. Although there may be some cantilevered planet carriers that mount the sun gear within the planet carrier. 
     The present design further reduces the axial length of the overall assembly design. For example, in a conventional modular gear head and motor combination such as a NEMA standard size 34 frame, these same two bearings would be axially separated by a distance of typically several inches. Thus, the present invention reduces the overall size by 10-20% of the entire length of a conventional modular gear head and motor combination. 
     In another embodiment of the present invention, the housing is completely sealed. Additionally, the housing is provided with input port  109  and an output port (also designated  109  and best seen in FIGS.  4  and  13 ). Thus, all of the moving components within the actuator  50  can be effectively lubricated and cooled with a simple low pressure oil circulation system (best seen in FIG. 14 at block  125 ). In a conventional gear head and motor assembly, this type of lubrication cannot be accomplished. Thus, the present invention is able to operate at greatly increased power levels. For example, the integrated rotary servo actuator  50  can continuously produce three times the torque at the same speeds as compared with the conventional motor and gear head combination. Additionally, effective lubrication extends the life of the moving components of the assembly. Thus, the present invention also provides for a more cost-efficient servo motor and gear head assembly as compared to conventional gear head and motor combinations. 
     FIGS. 5,  6   a ,  6   b , and  6   c , illustrate cross sectional views taken at different points along the longitudinal axis of the integrated rotary servo actuator  50 . FIG. 6 a  illustrates the arrangement and configuration of the sun gear  116 , the planet gears  123 , and the outer ring gear  126 . FIG. 6 b  illustrates the location of the sun gear bearing  115  as being within or proximately within the bearing  121 . FIG. 6 c  illustrates the location of the rotor  113  within the stator  112 . 
     FIGS. 7 and 8 illustrate exploded views of the gearhead assembly  51  and the front end plate  104 . The location of the bearings  121  and  122 , as well as the location of the front oil seal  130  are illustrated in FIG. 7, while the planetary gear carrier  120  is shown in its operative position within the ring gear  126 . FIG. 8 illustrates the planetary gear carrier  120  taken out of the operative position and to show the various elements of carrier  120 . More specifically, planet pins  131  are located within caged needle bearings  132 , which are then located within the planet gears  123 . 
     FIG. 9 shows an enlarged perspective view of the planet carrier device  120  with the planet gears  123  mounted therein and the integral output shaft  101 . FIG. 10 is an exploded perspective view from the back or rear of the actuator  50 . This view also shows the location of the bearings  121  and  122  on opposing sides of the planet carrier  120  in order to support the planet carrier. As indicated above, by straddling the planet gears  123 , the shaft side load on the actuator  50  is improved. 
     FIG. 11 is an exploded view of the feedback assembly  54  and the back end plate  108 . The location of encoder  134 , electrical connections  112  (feedback connector from the encoder to the controller  124 ) and  111  (providing power from the amplifier  124  to the windings  112 ), snap ring  132 , and rear oil seal  133  are all illustrated. 
     Alternative Embodiments 
     FIGS. 12 a ,  12   b  and  13  illustrate alternative embodiments of an actuator  50 ′ constructed in accordance with the principles of the present invention. Since the various parts illustrated in these drawings are similar to the parts identified above, the parts are represented by similar part numbers with a following prime designation. These schematic drawings illustrate that the locations of the various bearings may slightly differ from the embodiment described in detail above without departing from the principles of the present invention. For example, each of FIGS. 1 2   a  and  13  illustrate that larger bearings  121 ′ and  122 ′ straddle the planet carrier  120 ′. Similarly, the sun gear bearing  115 ′ is located axially (or longitudinally) at the same point to be approximately concentric with the larger bearing  121 ′ (or  122 ′). Still further, the rear rotor bearing  114 ′ is located within the physical area axially (or longitudinally) as the windings  112 ′. 
     In view of the foregoing embodiments, it will be appreciated that different approaches for mounting the sun gear bearing may be used. For example, the bearing may be located on the rotor side of the sun gear or located on the output shaft side of the sun gear. In some instances, the placement of the sun gear bearing may provide for manufacture of an integral rotor and sun gear (e.g., the embodiment shown in FIG.  13 ). In each case, however, the sun gear bearing is kept axially within the planet carrier. It will also be appreciated that moving the sun gear bearing to a location approximately within the planet carrier and moving the rear rotor bearing to a location approximately within the windings should be included within the scope of the present invention. 
     As noted above, the present invention is applicable to a number of different embodiments for a fully integrated servo motor and gear head assembly. Accordingly, the present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification. The claims are intended to cover such modifications and devices.