Abstract:
An actuator assembly includes a motor assembly, a harmonic drive gearbox, an actuator, and an electromagnet brake device. The actuator assembly is fairly compact in size and the electromagnetic brake device is a non-contact type of devices, making it less prone to wear as compared to many other brake devices.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to actuator assemblies, and more particularly to a relatively small, compact, and electromagnetically braked actuator assembly. 
       BACKGROUND 
       [0002]    Actuator assemblies are used in myriad devices and systems. For example, many vehicles including, for example, aircraft, spacecraft, watercraft, and numerous other terrestrial and non-terrestrial vehicles, include one or more actuator assemblies to effect the movement of various control surfaces or components. In many applications, the actuator assemblies include power drive units, such as motors, that are configured to receive a source of drive power to move an actuator, and thus the control surfaces or components, to a commanded position. When the control surfaces or components reach the commanded position, the source of drive power may be removed. Thus, many of the actuator assemblies that are used include what is sometimes referred to as a no-back device. The no-back device is configured to hold the actuator in position against the load once the actuator has moved the control surface or component to the commanded position. 
         [0003]    The types and configurations of no-back devices that are included in actuator assemblies vary. One particular type of no-back device that is used is a permanent magnet device. This type of device typically includes one or more permanent magnets that prevent rotation of the power drive unit when the source of drive power is removed. Another type of no-back device is a multi-rotor friction brake. Although these types of no-back devices, as well as the various other device types that are currently known, are generally safe, reliable, and robust, these devices do suffer certain drawbacks. For example, the presently known devices permanent magnet devices supply a continuous magnetic force against power drive unit rotation, in at least one rotational direction, that the power drive unit may need to overcome each time it is supplied with drive power. As a result, the size of the power drive unit may be larger than what is needed to move the load alone, in order to overcome this magnetic force, which can increase overall actuator and system size, weight, and costs. Moreover, the friction type devices can wear relatively quickly, resulting in the need to replace the devices, which can increase overall costs. 
         [0004]    In addition to the above, many actuators include an interposing element, such as a gear assembly or screw, between the power drive unit and the actuator. In many instances, it is desirable to physically implement an actuator that has a relatively small size and low weight. In the past, these goals have been met by using a relatively small electric motor that rotates at a relatively high rotational speed, and then including some type of gear reduction to increase the output torque of the actuator. 
         [0005]    Hence, there is a need for a no-back device that does not supply force against drive unit rotation, and/or is less prone to wear, and/or does not result in increased overall actuator assembly and system size, weight, and/or costs. There is also a need for an actuator assembly that includes a small, high speed motor with sufficient gear reduction that has a relatively small space envelope and/or relatively smaller weight as compared to known actuator assembly configurations. The present invention addresses at least one or more of these needs. 
       BRIEF SUMMARY 
       [0006]    In one embodiment, and by way of example only, an actuator assembly includes a motor assembly, a harmonic drive gearbox, an actuator, a latch rotor, one or more permanent magnets, and a latch electromagnet. The motor assembly includes a motor and a motor shaft, and the motor is configured to supply a first torque to the motor shaft. The harmonic drive gearbox is coupled to receive the first torque from the motor shaft and is operable, in response thereto, to supply a second torque. The actuator is coupled to receive the second torque from the harmonic drive gearbox and is configured, in response thereto, to move to a position. The latch rotor is coupled to the motor shaft to rotate therewith. The one or more permanent magnets are spaced apart from, and at least partially surround, the latch rotor, and supply a permanent magnetic field that opposes rotation of the latch rotor. The latch electromagnet is adapted to receive a flow of electrical current and, upon receipt thereof, to generate a magnetic field that opposes the permanent magnetic field supplied from the permanent magnets. 
         [0007]    In another exemplary embodiment, an actuation control system includes a motor assembly, a control circuit, a harmonic drive gearbox, an actuator, a latch rotor, one or more permanent magnets, and a latch electromagnet. The motor assembly includes a motor and a motor shaft. The motor is configured to be controllably energized and, in response to being controllably energized, to supply a first torque to the motor shaft. The control circuit is adapted to receive input signals and is operable, in response thereto, to controllably energize the motor and to selectively supply latch control signals. The harmonic drive gearbox is coupled to receive the first torque from the motor shaft and is operable, in response thereto, to supply a second torque. The actuator is coupled to receive the second torque from the harmonic drive gearbox and is configured, in response thereto, to move to a position. The latch rotor is coupled to the motor shaft to rotate therewith. The one or more permanent magnets are spaced apart from, and at least partially surround, the latch rotor. The permanent magnets supply a permanent magnetic field that opposes rotation of the latch rotor. The latch electromagnet is adapted to receive a flow of electrical current and, upon receipt thereof, to generate a magnetic field that opposes the permanent magnetic field supplied from the permanent magnets. 
         [0008]    In yet a further exemplary embodiment, an actuator assembly includes a motor assembly, a harmonic drive gearbox, an actuator, a latch rotor, one or more permanent magnets, and a latch electromagnet. The motor assembly includes a pancake motor and a motor shaft. The pancake motor is configured to supply a first torque to the motor shaft. The harmonic drive gearbox is coupled to receive the first torque from the motor shaft and is operable, in response thereto, to supply a second torque. The actuator is coupled to receive the second torque from the harmonic drive gearbox and is configured, in response thereto, to move to a position. The latch rotor coupled to the motor shaft to rotate therewith. The one or more permanent magnets are spaced apart from, and at least partially surround, the latch rotor. The permanent magnets supply a permanent magnetic field that opposes rotation of the latch rotor. The latch electromagnet is adapted to receive a flow of electrical current and, upon receipt thereof, to generate a magnetic field that opposes the permanent magnetic field supplied from the permanent magnets. The latch electromagnet includes a latch stator and a plurality of latch windings. The latch stator is non-rotationally mounted adjacent to, and at least partially surrounds, the latch rotor. The latch windings are wound around at least a portion of the latch stator, and are adapted to receive the flow of electrical current and, upon receipt thereof, to generate the magnetic field. The permanent magnets are mounted on the latch stator and are disposed adjacent each of the latch windings. 
         [0009]    Furthermore, other desirable features and characteristics of the actuator assembly will become apparent from the subsequent detailed description and appended claims, taken in conjunction with the accompanying drawings and preceding background. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0011]      FIG. 1  is a functional block diagram of an exemplary actuation control system according to an embodiment of the present invention; 
           [0012]      FIG. 2  is an exploded view of an exemplary harmonic drive that may be used to implement the actuator shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a cross section end view of the exemplary harmonic drive of  FIG. 2 ; 
           [0014]      FIGS. 4 and 5  are perspective and end views, respectively, of an exemplary physical implementation of an electromagnetic latch mechanism that may be used to in the system of  FIG. 1 ; and 
           [0015]      FIGS. 6 and 7  are end views of exemplary alternative embodiments of the electromagnetic latch mechanism depicted in  FIGS. 4 and 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0017]    Turning now to  FIG. 1 , a functional block diagram of an exemplary actuator control system  100  is shown. The system  100 , which may be used to control the movement of any one of numerous non-illustrated components, includes an actuator assembly  102  and a control circuit  150 . The actuator assembly  102  includes a power drive unit  104 , a harmonic drive gearbox  106 , an actuator  108 , and a latch mechanism  110 . The power drive unit  104  is preferably implemented as a motor  104 , is preferably enclosed within a motor housing  112 , and includes an output shaft  114 . The motor  104  is preferably implemented as an electric motor, and may be any one of numerous types of AC or DC motors now known or developed in the future including, for example, an AC induction motor, a brushed DC motor, or a brushless DC motor. Moreover, in a preferred embodiment, the motor  104  is implemented as a pancake motor. As is generally known, a pancake motor has a relatively large diameter compared to its thickness, and thus has a fairly compact space envelope. 
         [0018]    No matter how the motor  104  is specifically implemented, it is configured, upon being properly energized, to rotate and thereby supply a torque to the motor shaft  114 . The motor shaft  114  extends from the motor housing  112 , and is coupled to the harmonic drive gearbox  106 . In response to the torque supplied from the motor shaft  114 , the harmonic drive gearbox  106  supplies a torque, at a significantly reduced rotational speed from that of the motor shaft  114 , to the actuator  108 . To implement this rotational speed reduction, the harmonic drive gearbox  106  includes a plurality of interconnected components, all disposed within a housing  116 . For completeness, an exemplary embodiment of these internal components will now be briefly described. 
         [0019]    With reference now to  FIGS. 2 and 3 , exploded and end views, respectively, of an exemplary embodiment of the interconnected internal components of the harmonic drive  106  are shown. The harmonic drive gearbox  106 , which may be physically implemented in any one of numerous structural configurations now known or developed in the future, includes a wave generator  202 , a flexspline  204 , and a circular spline  206 . The wave generator  202  is coupled to, and thus rotates with, the motor shaft  114  and has an outer surface that is generally elliptically shaped. The wave generator  202  is disposed within the flexspline  204 . 
         [0020]    The flexspline  204  is coupled to, and thus supplies a drive force to, the actuator  108 . The flexspline  204  is implemented as a relatively thin-walled cylinder, and includes a plurality of gear teeth  208  formed on the outer surface of a portion thereof. The flexspline  204  is configured such that it is radially compliant, yet torsionally stiff. Thus, as  FIG. 2  shows, the when the wave generator  202  is disposed within the flexspline  204 , the flexspline outer surface conforms to the same elliptical shape as the wave generator  202 . 
         [0021]    The circular spline  206  surrounds the flexspline  204  and, at least in the depicted embodiment, is mounted against rotation. A plurality of gear teeth  212  are formed into the inner surface of the circular spline  206 , and mesh with the flexspline gear teeth  208  along the major axis of the ellipse. Because the flexspline  204  has less gear teeth  208  than the circular spline  206 , a reduction in rotational speed between the input and output of the harmonic drive  106  is achieved. Although the difference in number of gear teeth may vary, in a typical configuration, there are two less flexspline gear teeth  208  than circular spline gear teeth  212 . 
         [0022]    Before returning to the description of the actuation control system  100 , it will be appreciated that the above-described harmonic drive gearbox  106  is merely exemplary of a particular embodiment, and that harmonic drive gearboxes  106  of various other configurations and implementations could be used. Moreover, although the above-described harmonic drive gearbox  106  is configured such that the flexspline  204  is coupled to the actuator  108 , it will be appreciated that the harmonic drive gearbox  106  could also be configured such that the circular spline  206  is coupled to the actuator  108 . 
         [0023]    Returning once again to  FIG. 1 , the actuator  108 , as was noted above, is coupled to receive a torque, at a significantly reduced rotational speed from that of the motor shaft  114 , from the harmonic drive gearbox  106 . The actuator  108 , in response to this torque, is configured to move to a position. It will be appreciated that the actuator  108  may be implemented as any one of numerous types of actuators now known or developed in the future. For example, the actuator  108  could be implemented as any one of numerous types of rotary actuators and/or numerous types of linear actuators, just to name a few. 
         [0024]    The latch mechanism  110  is preferably disposed within the motor housing  112  and includes a latch rotor  122 , an electromagnet  124 , and a plurality of permanent magnets  126 . The latch rotor  122  is preferably coupled to, or integrally formed as part of, the motor output shaft  114 , though it could be coupled to, or integrally formed as part of, any one of numerous other components to effect its function, which is described in more detail further below. In the depicted embodiment the latch rotor  122  is coupled to an end of the output shaft  114  that is opposite to the end that is coupled to the harmonic drive gearbox  106 . It will be appreciated, however, that this is merely exemplary, and that the rotor could be mounted on the same end of the output shaft  114  that is coupled to the harmonic drive gearbox  106 . No matter on which end of the motor output shaft  114  it is mounted, the latch rotor  122  is preferably constructed, at least partially, of a magnetically permeable material. 
         [0025]    The electromagnet  124  is non-rotationally mounted on, for example, the motor housing  112 , and at least partially surrounds the latch rotor  122 . The electromagnet  124  is configured, upon being energized with a flow of direct current (DC) from a DC power source, to generate a magnetic field. It will be appreciated that the DC power source may be any one of numerous types of power sources, and may be implemented as part of or remote from the system  100 . In the depicted embodiment, the DC power source, as will be described below, is implemented within the control circuit  150 . No matter the specific source of the DC current, the magnetic field that is generated opposes the magnetic field that is generated by the permanent magnets  126 , thus allowing uninhibited rotation of the motor  104 . 
         [0026]    The permanent magnets  126  are coupled to the electromagnet  124  and are spaced apart from, and at least partially surround, the latch rotor  122 . The permanent magnets  126  are configured to supply a permanent magnetic field that opposes rotation of the latch rotor  122 . Thus, when no DC current is supplied to the electromagnet  124  and the motor  104  is not energized for rotation, the permanent magnetic field supplied from the permanent magnets  126  holds the latch rotor  122 , and thus the motor output shaft  114 , is held in place. As noted above, the electromagnet  124  is energized to generate a magnetic field having a polarity opposite to that of the permanent magnets  126 , to allow motor  104  rotation with no resistance from the latch mechanism  110 . 
         [0027]    The control circuit  150  controllably energizes the motor  104  and supplies latch control signals to the latch mechanism  110 . The control circuit  150  may be configured to receive external control signals from one or more external sources (not shown in  FIG. 1 ). In response to these control signals, the control circuit  150  controllably energizes the motor  104  and supplies the latch control signals to the latch mechanism  110 . The motor  104 , upon being energized, rotates in the direction that will cause the actuator  108  to move to a desired position. The latch control signals may be in the form of DC current that flows through the electromagnet  124 , or in the form of a control signal that causes a separate power source to supply the DC current flow through the electromagnet  124 . In either case, the DC current flow, as noted above, appropriately energizes the electromagnet  124  to generate a magnetic field that opposes the permanent magnetic field supplied from the permanent magnets  126 . The control circuit  150 , using feedback signals supplied from, for example, a suitably configured actuator position sensor  118 , implements closed-loop control to move the actuator  108  to the desired position. 
         [0028]    When the actuator  108  attains the desired position, the control circuit  150  no longer controllably energizes the motor  104 , but continues to supply latch control signals to the electromagnet  124 . More specifically, the latch control signals supplied to the electromagnet  124  now generates a magnetic field that interacts with and aids the permanent magnetic field supplied from the permanent magnets  126 . The magnetic fields together interact with the latch rotor  122  and prevent further rotation of the motor output shaft  114 . It will be appreciated that the control circuit  150  may be configured to implement any one of numerous control schemes. 
         [0029]    With reference to  FIGS. 4-7 , various exemplary embodiments of particular physical implementations of the latch mechanism  110  described above are depicted, and will now be described in more detail. The latch rotor  122 , as noted above, is configured to be mounted on the motor output shaft  114 , and includes a main body  402  and a plurality of lobes  404  extending radially therefrom. As noted above, the latch rotor  122  is at least partially constructed of a magnetically permeable material. In this regard, at least the lobes  404 , or at least portions thereof, are constructed of a magnetically permeable material. It will be appreciated, however, that the entire latch rotor  122  could be constructed of a magnetically permeable material. 
         [0030]    The electromagnet  124  includes a latch stator  406 , and a plurality of latch coils  408 . The latch stator  406  is configured to be mounted on the motor housing  112 , and at least partially surrounds the latch rotor  122 . The permanent magnets  126  are preferably disposed within the latch stator  406 , and the latch coils  208  are wound around the latch stator  406  adjacent each of the permanent magnets  126 . The latch coils  408  are wound in a manner that, upon being energized with DC current, the latch coils  408  generate the same number of magnetic pole pairs as there are permanent magnets  126 , and in a manner that opposes or aids the permanent magnetic field supplied from each permanent magnet  126 . When current flows through the latch coils  408  in one direction, the generated magnetic pole pairs oppose the permanent magnetic field supplied from each permanent magnet  126 , and when current flows through the latch coils  408  in the opposite direction, the generated magnetic pole pairs aid the permanent magnetic field supplied from each permanent magnet  126 . In  FIGS. 4 and 5  it is seen that the latch rotor  122  includes six lobes  404 , thus there are three permanent magnet pole pairs and the latch coils  408  are wound on the latch stator  406  in a manner that generates three magnetic pole pairs. Alternatively, in the embodiment depicted in  FIG. 6  the latch rotor  122  includes four lobes  404 , so there are two permanent magnet pole pairs and the latch coils  408  are wound on the latch stator  406  in a manner that generates two magnetic pole pairs, and in the embodiment depicted in  FIG. 7 , the latch rotor  122  includes eight lobes  404 , so there are four permanent magnet pole pairs and the latch coils  408  are wound on the latch stator  406  in a manner that generates four magnetic pole pairs. 
         [0031]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.