Abstract:
The actuator has a shaft having a starting point resistance feature, and a low resistance portion. The actuator has a motor configured to rotate the shaft, the motor outputting a current feedback signal to indicate current exiting the motor. The actuator has a interference portion in proximity to the shaft, the interference portion configured to facilitate a resistance to shaft rotation when the shaft rotates, the resistance to shaft rotation causing a magnitude of the current signal to be greater when the starting point resistance feature passes in front of the interference portion than when the low resistance portion passes in front of the interference portion.

Description:
BACKGROUND 
       [0001]    Actuators are used to allow mechanical devices to achieve motion such as rotational motion and linear motion. For example one conventional actuator used to achieve linear motion is a bolt and screw actuator. A bolt and screw actuator transforms rotational motion from a motor such as a simple electric motor into linear motion. The screw portion of the bolt and screw actuator is a threaded shaft that is rotated by the motor. The bolt portion of the bolt and screw actuator is a hollow cylinder with a threaded inner surface that matches with the threaded shaft. Rotation of the screw portion as it engages the bolt portion creates linear motion along the axis of the bolt portion and screw portion. 
         [0002]    Some actuators, such as the bolt and screw actuator, are regulated by an electronic controller. The controller sends and receives data with the actuator to permit controlled regulation. For example a controller can be used to control the distance or speed that an actuator will move. 
         [0003]    Actuators used to provide motion in mechanical devices may need to be initialized to be in some specific position. Since actuators cannot by themselves sense the position that they are in, mechanical stops are typically used to physically block the motion of an actuator at a certain point to locate the position. 
       SUMMARY 
       [0004]    Unfortunately there are deficiencies to the above-described conventional approaches to using a mechanical stop to initialize an actuator in some specific position. For example, with such an approach the mechanical stop will prevent a wider range of motion that would have otherwise been possible if the mechanical stop was not there. For example if the mechanical stop were placed on the rotating element of a bolt and screw actuator, the possible rotation of the shaft would be less than 360°. Applications that would require more than 360° rotation would not be possible. This would require designers to make expensive modifications to certain applications to work with existing actuators. 
         [0005]    Another deficiency to the above-described conventional approaches to using a mechanical stop to initialize an actuator in some specific position is the inability to differentiate between the mechanical stop and a physical jamming of the actuator. Both the actuator running into the mechanical stop and the physical jamming of the actuator results in a complete stop in the motion of the actuator. This creates a reliability concern since the actuator cannot be certain that it has initialized to the correct location or that it has jammed in some other location. This could result in fewer feasible applications of the actuators in systems that require a high degree of reliability. 
         [0006]    Yet another deficiency to the above-described conventional approaches to using a mechanical stop to initialize an actuator in some specific position is the difficulty in knowing the actual position of the internal workings of the valve device module after the actuator package module is removed. One way to be sure where the valve elements are positioned is to incorporate a hardware-based indication on the interface parts between the two modules to determine orientation. This is expensive to fabricate and reduces universality of the actuator package. Another way to be sure where the valve elements are position is to remove the entire valve assembly from the system to visually verify the position of the valve device module internal elements before the actuator module is mated to it. This is an expensive and time consuming procedure that requires draining and opening of the system piping. 
         [0007]    In contrast to the above-identified conventional approaches to using a mechanical stop to initialize an actuator in some specific position, an improved actuator initialization technique involves using a detent to provide a resistance to rotation but not stop rotation. Such a detent structure would not limit rotation of the shaft and would allow for rotations greater than 360°. Additionally since the initialization point in relation to the detent causing resistance does not stop rotation, a differentiation can be made between identifying when the actuator has been initialized and when the actuator has jammed. Additionally, since the detent is in a known location, the actuator package can be removed and replaced without removing the entire valve device from the system, thereby maintaining system integrity. 
         [0008]    One embodiment is directed to an actuator. The actuator has a shaft having a starting point resistance feature, and a low resistance portion. The actuator has a motor configured to rotate the shaft, the motor outputting a current signal to indicate current exiting the motor. The actuator has a detent in proximity to the shaft, the detent configured to facilitate a resistance to shaft rotation when the shaft rotates, the resistance to shaft rotation causing a magnitude of the current signal to be greater when the starting point resistance feature passes in front of the detent than when the low resistance portion passes in front of the detent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing and other objects, features and advantages will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the invention. 
           [0010]      FIG. 1  is a perspective view of an electronic system having an actuator and a valve device. 
           [0011]      FIG. 2  is a perspective view of the actuator of  FIG. 1  with a fixed member interacting with a shaft. 
           [0012]      FIG. 3  is a cross section side view of a portion of the electronic system of  FIG. 1  when the fixed member having a ball and a spring, engages the shaft. 
           [0013]      FIG. 4  is a cross section top view of a portion of the electronic system of  FIG. 1  when the motor having a set of poles and a set of hall sensors, engages the controller having a flash storage. 
           [0014]      FIG. 5  is a chart representing four distinct current feedback signal measurements that can be identified by the electronic system. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    An improvement to an actuator assembly replaces the need for a mechanical stop to initialize the actuator with a resistance causing detent. Accordingly, the actuator preserves its full range of motion. The resistance causing detent can be incorporated into the actuator assembly in at least two different orientations. As will be described in further detail in  FIG. 1 , one orientation incorporates the resistance causing detent into a valve device. 
         [0016]      FIG. 1  shows an electronic system  20  which includes a controller  28 , and an actuator  42 . The actuator  42  includes a motor  24  to power a rotatable shaft  22  which interfaces with valve device  64 . As will be explained in further detail shortly, the rotatable shaft  22  interfaces with a rotatable shaft  66  of the valve device  64  at a shaft interface  38 . A resistance portion  32  (e.g., an indentation) on the rotatable shaft  66  interfaces with a fixed member  68 . An anchoring region  50  and an interference portion  26  (e.g., a spring loaded protrusion) form the fixed member  68 . It should be understood that a gear assembly  30  is illustrated as an arrangement of integrated gears (e.g., a gear box) by way of example only, and that other arrangements for the gear assembly  30  are suitable for use as well. The electronic system  20  interfaces with other devices via the shaft interface  38  on the shaft  22 . The controller  28  has integrated motor  24  current sensing capability. The shaft  22 , the motor, and the gear assembly  30  form the core components for an actuator  42 . The fixed member  68 , the shaft  66 , and resistance portion  32  form the valve device  64 . 
         [0017]    During operation, the controller  28  is arranged to provide a drive signal  34  to the motor  24 , and sense the motor current and a Hall Effect feedback signal  36  from the motor  24 . In response to the drive signal  34 , the motor  24  drives the gear assembly  30  causing the rotatable shafts  22  and  66  to rotate in a particular direction (e.g., clockwise). As the rotatable shafts  22  and  66  turn, the resistance portion  32  periodically passes by the interference portion  26  of the fixed member  68  placing increased mechanical resistance or drag on the motor  24  and a changing in the current sensed by the controller  28 . Such operation enables the controller  28  to determine a consistent initial position (i.e., a zero position) of the gear assembly  30 . Nevertheless, the rotatable shaft  22  is able to freely rotate through the additional mechanical resistance without encountering a hard stop. As a result, the rotatable shafts  22  and  66  enjoy a wider range of motion. 
         [0018]    In some arrangements, the drive signal  34  is an electric current which drives the motor  22 . In these arrangements, the direction of the electric current determines the direction of rotation of the rotatable shafts  22  and  66 . Furthermore, while the uniform portion of the rotatable shaft  22  passes by the interference portion  26 , the sensed magnitude of the current is substantially uniform and at a relatively low level. However, when the resistance portion  32  of the rotatable shaft  22  engages with the interference portion  26 , the sensed magnitude of the current increases thus enabling the controller  28  to detect when the particular angular displacement/position of the rotatable shaft  22 , i.e., the zero position. Moreover, now that the behavior of the current is known, the controller  28  is capable of factoring in this behavior to mask out or ignore further encounters if the rotatable shaft  22  needs to rotate more than  360  degrees. Further details will now be provided with reference to  FIG. 1 . 
         [0019]    As shown in  FIG. 1 , the shaft  22  acts through the shaft interface  38  to provide mechanical motion for connected devices (e.g. valves). The mechanical motion can be in many forms including but not limited to rotational motion (e.g. provided by a solid shaft  22 ) and linear motion (e.g. provided by a screw and bolt shaft  22 ). In one embodiment the shaft  22  is directly rotated by the motor  24 . Alternatively in another embodiment, the shaft  22  is rotated at a different speed than the motor  24  if it is connected by the gear assembly  30 . High reduction gearboxes  30  allows for smaller motors  24  with higher torques. 
         [0020]    As shown in  FIG. 1 , the interference portion  26  engages the shaft  66  as the shaft  66  rotates. As the resistance portion  32  passes in front of interference portion  26 , there is an increase to the resistance of rotation of the shaft  66 . There is also resistance to rotation caused by the interference portion  26  when other areas of the shaft  66  pass in front of the interference portion  26 , but the magnitude of this resistance is less than in the previous scenario. 
         [0021]    The current usage level of the motor  24  is sensed by the controller  28  and corresponds to resistance to shafts  22  and  66  rotation powered by the motor  24 . The controller  28  is able to differentiate between four discrete current levels. The lowest magnitude of the current corresponds to the operating current necessary to move the shafts  22  and  66  during normal operation (i.e. when areas other than the resistance portion  32  passes in front of interference portion  26 ). The low intermediate magnitude of the current corresponds to the breakout current which includes additional current draw caused by “sticktion” of the seals and bearings that occurs when the shafts  22  and  66  first start to move. The high intermediate magnitude of the current corresponds to the increase in resistance to shafts  22  and  66  rotation when the resistance portion  32  passes in front of interference portion  26 . The highest magnitude of the current corresponds to a shaft rotation that is frozen or jammed. 
         [0022]    As shown in  FIG. 1 , the drive signal  34  is a signal from the controller  28  that gives operating instructions to the motor  24 . When initial power is applied to the actuator  42 , the controller  28  sends the drive signal  34  to instruct the motor  24  to rotate. If the controller  28  receives the discrete high intermediate magnitude of the current signaling that the resistance portion  32  passed in front of the interference portion  26 , the controller  28  will signal the motor  24  to reverse rotation a set number of rotational counts to return to the required mechanical zero. Conversely, if the controller  28  receives the discrete highest magnitude of the current signaling that shaft  22  rotation has frozen or jammed, the controller  28  will signal the motor to draw less current to prevent overheating. 
         [0023]    This orientation incorporating the resistance causing detent into the valve device  64  allows the actuator  42  to be used with existing valve devices  64  that have the interference portion  26  and with new valve devices  64  designed with the interference portion  26 . As will be described in further detail in  FIG. 2 , another orientation incorporates the resistance causing detent into the actuator  42 . 
         [0024]      FIG. 2  shows the electronic system  20  which includes the controller  28 , and the actuator  42 . The actuator  42  includes a motor  24  to power the rotatable shaft  22  which interfaces with the valve device  64  (not shown in  FIG. 2 ). As will be explained in further detail shortly, the rotatable shaft  22  has the resistance portion  32  (e.g., an indentation) that interacts with fixed member  68 . The anchoring region  50  and the interference portion  26  (e.g., a spring loaded protrusion) form the fixed member  68 . It should be understood that the gear assembly  30  is illustrated as an arrangement of integrated gears (e.g., a gear box) by way of example only, and that other arrangements for the gear assembly  30  are suitable for use as well. The electronic system  20  interfaces with other devices via the shaft interface  38  on the shaft  22 . The controller  28  has integrated motor  24  current sensing capability. The shaft  22 , resistance portion  32 , the motor, the gear assembly  30 , and the fixed member  68  form the core components for an actuator  42 . 
         [0025]    The fixed member  68  interacts with the resistance portion  32  on shaft  22  in the same way as previously described with the resistance portion  32  on shaft  66  (See  FIG. 1 ). In this orientation, the actuator  42  can interact with existing valve devices  64  that do not have the interference portion  26  or for valve device  64  designs that have space limitations that preclude having the interference portion  26 . In some arrangements, the interference portion  26  is designed to be removable to allow the use of the actuator  42  in multiple applications. 
         [0026]      FIG. 3  shows the interference portion  26  engaging the shaft  66  at the resistance portion  32 . The interference portion  26  is composed of a ball  44 , a spring  46 , and a protrusion chamber  48 . The interference portion  26  is rigidly attached to the anchoring region  50 . 
         [0027]    As shown in  FIG. 3 , one possible configuration for the interference portion  26  is the ball  44  interference portion  26  with spring  46  loading. The ball  44  freely rotates at the end of the chamber  48 . The ball  44  can be pushed further into the protrusion chamber  48 , but cannot fall out of the chamber  48 . The ball  44  is pushed to the end of the protrusion chamber  48  by the spring  46  disposed inside of the chamber. There are other types of interference portion  26  configurations possible such as a wheel or solid interference portion  26  that may be used in other embodiments. 
         [0028]    As shown in  FIG. 3 , one possible configuration of the resistance portion  32  is an indentation  32 . The indentation  32  works well with the ball  44  interference portion  26  with spring  46  loading formation of the interference portion  26 . The indentation  32  is large enough for the ball  44  to fall into. Other types of starting point resistance features  32  such as a protrusion, vertically oriented slot, such as for a keyway, or adhesive area may be used in other embodiments. 
         [0029]    As shown in  FIG. 3 , one possible configuration of the spring  46  is the adjustable spring  46 . The adjustable spring  46  allows the spring constant to be tuned so that the high intermediate magnitude of the current feedback signal  40 , corresponding to the increase in resistance to shaft  22  rotation when the resistance portion  32  passes in front of interference portion  26 , can yield a specific motor current level. 
         [0030]    As shown in  FIG. 3 , the ball  44  of the interference portion  26  rolls along shaft  66  as the shaft  22  rotates. When the ball  44  falls into the indentation  32  there is no significant increase resistance to shaft  22  rotation and thus no significant increase in current feedback signal  40 . However, when the ball  44  moves out of the indentation  32 , the ball  44  will push against the wall of the indentation  32 . This will cause an increase in resistance to shaft  22  rotation and thus an increase in current level sensed by the controller  28 . The increase in current followed by reduction of current to the normal operating level would be recognized by the controller  28  as the high intermediate magnitude of the current. 
         [0031]      FIG. 4  shows the motor  24  connected to the controller  28 . The motor  24  includes a set of poles  52  (i.e., two or more poles  52 ), a set of Hall Effect sensors  54  (i.e., one or more Hall Effect sensors  54 ), a magnet  56 , a motor rotation  58 , and a set of wires  60  (i.e., one or more wires). The controller  28  contains a flash storage  62 . 
         [0032]    As shown in  FIG. 4  one possible configuration for the motor  24  is the brushless DC motor  24 . The brushless DC motor  24  is a six pole  52  motor  24  that can rotate in both directions  58 . The brushless DC motor employs three Hall Effect sensors  54 . When this brushless DC motor  24  is used in conjunction with the 60:1 reduction gear assembly  30 , rotations of the shaft  22  as small as ⅓ of a degree can be detected by the controller  28 . There are other types of motors that may be used in other embodiments. 
         [0033]    As shown in  FIG. 4  the Hall Effect sensors  54  are used to identify when the pole  52  passes in front of the Hall Effect sensor  54  during motor rotation  58 . When the Hall Effect sensor detects the pole  52  in front of it, the Hall Effect sensor sends the Hall Effect feedback signal  36  to the controller  28  over the set of wires  60 . The controller  28  makes counts of the pole  52  passes by the Hall Effect sensors  54 . The controller can use these counts to calculate discrete distances that the shaft  22  has rotated. The controller can also use these counts to instruct the motor  24  to rotate the shaft  22  discrete distances. 
         [0034]    As shown in  FIG. 4  the controller  28  utilizes the flash storage  62 . The controller  28  can utilize the flash storage  62  record the count number. If there is a loss of external power, upon restoration of power, the controller can calculate the position of the shaft based on the stored count number assuming the shaft  22  has not been manually moved. The controller can then direct the motor  24  to rotate the shaft  22  to the approximate zero initialization point. The electronic system  20  can then initiate the startup sequence to use the interference portion  26  to find the true zero initialization point. 
         [0035]      FIG. 5  shows various current signals  40  that are detected by the controller  28 . The current signals include a normal operational current  40 A, a breakout current  40 B, a detent current  40 C, and a jammed current  40 D. 
         [0036]    As shown in  FIG. 5 , the normal operational current  40 A is the lowest current recognized by the controller  28 . The normal operational current  40 A will not cause the controller  28  to modify its instructions to the motor  24 . The breakout current  40 B is a slight increase over the normal operational current  40 A that occurs when the shaft  22  first starts to rotate and has to overcome static friction. The detent current  40 C is greater than the breakout current  40 B but less than the jammed current  40 D. The detent current indicates an increase in resistance to shaft  22  rotation when the resistance portion  32  passes in front of interference portion  26 . Upon detecting the detent current  40 C and the subsequent drop to operational current  40 A, the controller  28  will signal the motor  24  to reverse rotation a set number of rotational counts to return to the required mechanical zero. If controller  28  is not in the initialization process, and the commanded actuator position is greater than 360°, the controller  28  will ignore the detent current  40 C and continue to rotate to the commanded position. The jammed current  40 D is the highest current recognized by the controller  28 . The jammed current  40 D is also represented as a threshold current. Thus any current greater than this threshold will be viewed as the jammed current  40 D. If the controller  28  receives the jammed current  40 D, the controller  28  will signal the motor to draw less current to prevent overheating. 
         [0037]    While various embodiments of the invention have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
         [0038]    For example, the interference portion  26  can provide a resistance to create the intermediate magnitude of the current feedback signal  40  by engaging the shaft  22  that is rotating or moving linearly. 
         [0039]    In another example, the interference portion  26  and the resistance portion  32  are swapped. One embodiment of this example would have a spring  46  loaded ball  44  interference portion  26  attached to the rotating shaft  22 . The protrusion would engage the resistance portion  32  in the form of the cavity formation  32  that is embedded in the anchoring region  50 .