Abstract:
An actuator and its clutch are provided. The clutch includes a driving shaft; a mounting base fixed to the driving shaft for rotation with the driving shaft; a connecting base for connecting with a load, the connecting base including fingers surrounding an outer circumference of the driving shaft; resilient member including a resilient member, the resilient member having two ends respectively fixed to the mounting base and the connecting base, the resilient member surrounding an outer circumference of the connecting tabs. When a rotation speed of the driving shaft is greater than a rotation speed of the connecting base, an inner diameter of the resilient member gradually decreases so as to gradually couple the coupling portion with the driving shaft, such that the rotation speed of the coupling portion gradually approaches or reaches the rotation speed of the driving shaft. The present invention can provide a buffering function at the phase of the startup of the motor to avoid the motor startup failure and damage to the motor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201510502454.3 filed in The People&#39;s Republic of China on 14 Aug., 2015, and Patent Application No. 201510502051.9 filed in The People&#39;s Republic of China on 14 Aug. 2015. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to motors, and in particular to an actuator and a clutch thereof. 
       BACKGROUND OF THE INVENTION 
       [0003]    When the rotational inertia of a load is too large, startup of the motor may fail because the motor cannot provide sufficient rotation torque at the moment of startup, and the motor may also be damaged in such situation. 
         [0004]    When the motor is a single phase motor which usually has a small output torque, the above situation can more easily occur. 
       SUMMARY OF THE INVENTION 
       [0005]    Thus, there is a desire for an improved actuator which can drive a larger load by using a single phase motor. 
         [0006]    In one aspect, the present invention provides a clutch which includes a driving shaft; a connecting base for connecting with and driving a load, the connecting base comprising a coupling portion; and a resilient member comprising one end attached relative to the driving shaft for rotation with the driving shaft and the other end attached to the connecting base, the resilient member surrounding an outer circumference of the driving shaft and the coupling portion. When a rotation speed of the driving shaft is greater than a rotation speed of the connecting base, an inner diameter of the resilient member gradually decreases so as to gradually couple the coupling portion with the driving shaft, such that the rotation speed of the coupling portion gradually approaches or reaches the rotation speed of the driving shaft. 
         [0007]    Preferably, the coupling portion comprises a plurality of flexible fingers surrounding the outer circumference of the driving shaft. 
         [0008]    Preferably, the resilient member is a helical spring surrounding an outer circumference of the plurality of flexible fingers. 
         [0009]    Preferably, the connecting base includes a ring-shaped portion, and the plurality of fingers extends from one side of the ring-shaped portion. 
         [0010]    Preferably, an inner wall surface of the finger is an arc surface. 
         [0011]    Preferably, the clutch further includes a protective tube mounted around an outer circumference of the resilient member. 
         [0012]    In another aspect, the present invention provides an actuator including a motor and a clutch. The clutch comprises a driving shaft driven by the motor; a connecting base for connecting with and driving a load, the connecting base comprising a coupling portion; and a resilient member comprising one end attached to the driving shaft for rotation with the driving shaft and the other end attached to the connecting base, the resilient member surrounding an outer circumference of the driving shaft and the coupling portion. During the phase of the startup of the motor, the driving shaft is rotated relative to the connecting base which results in an inner diameter of the resilient member gradually decreasing so as to gradually couple the coupling portion with the driving shaft to cause the connecting base with the load to be rotated by the driving shaft. 
         [0013]    Preferably, the coupling portion comprises a plurality of flexible fingers surrounding the outer circumference of the driving shaft. 
         [0014]    Preferably, the motor is a single phase permanent magnet motor such as a single phase permanent magnet synchronous motor or a single phase permanent magnet direct current brushless motor. 
         [0015]    Preferably, the clutch further includes a protective tube mounted around an outer circumference of the resilient member. 
         [0016]    Preferably, the single phase motor comprises a stator, a permanent magnet rotor and a driving circuit, the stator comprising a stator winding adapted to be connected in series with an AC power source between a first node and a second node, the driving circuit comprising: a controllable bidirectional AC switch connected between the first node and the second node; an AC-DC conversion circuit connected in parallel with the controllable bidirectional AC switch between the first node and the second node; a position sensor configured to detect a magnetic pole position of the permanent magnet rotor; and a switch control circuit configured to control the controllable bidirectional AC switch to be switched between a switch-on state and a switch-off state in a predetermined way, based on the magnetic pole position of the permanent magnet rotor and the polarity of the AC power source such that the stator winding drives the rotor to rotate only in the predetermined direction. There is no current flowing through the AC-DC conversion circuit when the first node and the second node are short circuited by the controllable bidirectional AC switch. 
         [0017]    The present invention further provides an electric apparatus which employs the above actuator and a fluid generating device driven by the actuator. The fluid generating device may be a fan or an impeller. 
         [0018]    The clutch of the present invention can provide a buffering function at the phase of startup of the rotor of the single phase motor, which facilitates to avoid the motor startup failure and damage to the motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is pre-assembled view of an actuator in accordance with one embodiment of the present invention. 
           [0020]      FIG. 2  is an assembled view of the actuator of  FIG. 1 . 
           [0021]      FIG. 3  to  FIG. 5  illustrate the changing process of the clutch during the phase of motor startup. 
           [0022]      FIG. 6  is a pre-assembled view of an actuator in accordance with a second embodiment of the present invention. 
           [0023]      FIG. 7  is pre-assembled view of an actuator in accordance with a third embodiment of the present invention. 
           [0024]      FIG. 8  illustrates an inner rotor permanent magnet brushless motor utilized in the above embodiment. 
           [0025]      FIG. 9  is a block diagram showing a startup circuit of the motor of  FIG. 8 . 
           [0026]      FIG. 10  illustrates an outer rotor permanent magnet brushless motor utilized in the above embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Referring to  FIG. 1 , a single phase actuator in accordance with one embodiment of the present invention includes a single phase motor  10  and a clutch  50 . The motor  10  drives a load  40  to rotate via the clutch  50 . The single phase motor  10  is preferably a single phase direct current brushless motor or a single phase permanent magnet synchronous motor. 
         [0028]    The clutch  50  includes a driving shaft  51 , a mounting base  53 , a connecting base  55 , and a resilient member  59 . The driving shaft  51  is connected to the motor  10  and is driven by a rotor of the motor  10 . It should be understood that the driving shaft  51  may be an output shaft of the motor itself or an external driving shaft connected to the motor output shaft or motor rotor via a coupling. In this embodiment, the mounting base  53  is connected to the driving shaft  51  for rotation with the driving shaft  51 . It should be understood that the mounting base  53  may also be fixedly connected to other portions of the motor. The connecting base  55  is connected to the load  40  for driving the load  40  to rotate. The resilient member  59  is used to control the frictional force between the connecting base  55  and the driving shaft  51 , such that the driving shaft  51  is able to drive the connecting base  55  with the load  40  to rotate when the rotation speed of the driving shaft  51  increases to a predetermined value. In this embodiment, the motor  10  is a single phase permanent magnet synchronous motor or a single phase permanent magnet direct current brushless motor. 
         [0029]    The connecting base  55  includes a ring-shaped mounting portion and a plurality of fingers  57  extending outward from one side of the ring-shaped mounting portion. The fingers  57  extend in a direction toward the mounting base  53 . Gaps  58  are formed between adjacent fingers  57 . The presence of the gaps  58  allow the fingers  57  to deflect inwardly so as to reduce an inner diameter of a space defined by the plurality of fingers  57 . 
         [0030]    Referring to  FIG. 2 , the plurality of fingers  57 , acting as a coupling portion of the connecting base  55 , surrounds the driving shaft  51 . The resilient member  59  is attached around an outer circumference of the fingers  57 . In this embodiment, the resilient member  59  is a helical/coil spring. Two opposite ends of the helical spring  59  are attached to the mounting base  53  and the connecting base  55 , respectively. The helical spring  59  surrounds the outer circumference of the fingers  57 . 
         [0031]    When the actuator enters a working state (rotation) from a stationary state, the changing process of the clutch is as shown in  FIG. 2 ,  FIG. 3 ,  FIG. 4 , and  FIG. 5 , respectively. Specifically,  FIG. 2  illustrates the stationary state of the actuator where the motor is de-energized. When the motor  10  is energized to startup, the motor  10  drives the driving shaft  51  to rotate, the end of the resilient member  59  connected to the mounting base  53  rotates along with the mounting base  53 , causing the helical spring  59  to gradually shrink from the end connected to the mounting base  53 , such that the fingers  57  shrink/deform toward the driving shaft  51 . The shrinking of the plurality of fingers  57  causes the fingers  57  to hold/contact the driving shaft  51  with a frictional force therebetween gradually increasing. As the fingers  57  shrink more tightly, the frictional force between the fingers  57  and the driving shaft  51  becomes larger. When the frictional force between the fingers  57  and the driving shaft  51  is large enough, the connecting base  55  is rotated under the driving of the frictional force, such that the load  40  is rotated along with the connecting base  55 , as shown in  FIG. 3  and  FIG. 4 . When the load  40  (or connecting base  55 ) and the driving shaft  51  have the same rotation speed, the resilient member  59  maintains at a stable compressed/deformed state, as shown in  FIG. 5 . 
         [0032]    In order to increase the frictional force, an inner wall surface of the finger  57  is a rough arc surface with granular bulges/projections thereon. In addition, in order to facilitate the fingers  57  to return to its original state when the motor stops rotation, the fingers  57  are flexible. 
         [0033]    It should be understood that, when the actuator turns from the working state (rotation) into a stop state, the changing process of the clutch is as shown from  FIG. 5 ,  FIG. 4 ,  FIG. 3  to  FIG. 2 , respectively. That is, when the driving shaft  51  slows down or stops, the load  40  continues its rotation due to its inertia, resulting in a relative rotation between the connecting base  55  and the mounting base  53 . The resilient member  59  is gradually released from the end of the resilient member  59  connected to the connecting base  55  to the end connected to the mounting base  53  and finally returned to the state as shown in  FIG. 2 . 
         [0034]      FIG. 6  illustrates an actuator in accordance with a second embodiment of the present invention, which is similar to the first embodiment except adding a protective tube  61  around the outer circumference of resilient member  59 . When the motor  10  returns from the working state to the stop state, the driving shaft gradually stops rotating, and the load  40  together with the connecting base  55  continue rotating due to the inertia. During this course, the resilient member  59  is released from the shrinked state to its free state, the diameter of the resilient member  59  is gradually increased such that the fingers  57  gradually return to their original state and therefore release the driving shaft  51  to avoid rotating the driving shaft  51  in a reverse direction. If the rational inertia of the load  40  is too large, the end of the resilient member  59  connected to the connecting base  55  is continued to be rotated relative to the end of the resilient member  59  connected to the mounting base  53  after the resilient member  59  reaches its free/original state, which causes the resilient member  59  to be de-coiled and the diameter of the resilient member  59  to be increased compared to its original state. The resilient member  59  will probably be damaged. A protective tube  61  is preferably added to surround the resilient member  59  in order to limit/stop over increasing of the outer diameter of the resilient member  59 , thereby preventing permanent deformation and hence permanent loss of resiliency of the resilient member  59 . 
         [0035]    When the motor drives a larger load, in order to address the motor startup failure problem due to the fact that the output torque of the motor is not large enough to drive the load at the phase of the startup, the present invention allows the driving shaft  51  to slip relative to the load  40  at the beginning of the motor startup. Only when the output torque of the motor reaches a certain value, the motor  10  drives the load  40  to rotate synchronously via the clutch  50 , such that the motor can more easily and successfully start and drive a load with large rotational inertia without being damaged. In addition, by utilizing the actuator and its clutch provided by the present invention, there is no need to increase the size of the motor. 
         [0036]    Referring to  FIG. 7 , in a third embodiment of the present invention, the connecting base  55  includes a rod-shaped or tubular coupling portion  56  that is separate from and coaxial with the driving shaft  51 . The resilient member  59  is a helical spring helically surrounding the coupling portion  56  and driving shaft  51 . A connecting tube  63  with a variable inner diameter is disposed to surround the coupling portion  56  and the driving shaft  51 , i.e., the coupling portion  56  and the driving shaft  51  are respectively inserted into opposite ends of the connecting tube  63 . The connecting tube  63  is surrounded by the resilient member  59 . The connecting tube  63  tightly holds around the coupling portion  56  and the driving shaft  51  when the inner diameter of the resilient member  59  decreases. 
         [0037]    In this embodiment, the connecting tube  63  has a C-shaped cross-section. That is, a body of the connecting tube  63  has an axially extending slit  64 , so that the inner diameter of the connecting tube  63  is capable of decreasing to thereby tightly hold around the coupling portion  56  and the driving shaft  51 . Preferably, the connecting tube  63  is flexible so that it can return to its original state upon removal of the external force. 
         [0038]      FIG. 8  illustrates a single phase permanent magnet brushless motor  10  utilized in the above embodiment. The motor is of an inner rotor type. The motor  10  includes a stator  13  and a rotor  14 . The stator  13  includes a stator core such as a laminated stator core  15  and a winding  16  wound around the stator core  15 . The rotor  14  includes a rotary shaft  17  and permanent magnetic poles  18 . Outer surfaces of the permanent magnetic poles  18  confront the stator core  15  with an air gap formed there between to allow the rotor to rotate relative to the stator. Preferably, the air gap is a substantially even air gap, i.e. most part of the outer surfaces of the permanent magnetic poles  18  are coaxial with most part of an inner surface of the stator core  15 . The stator core  15  includes a yoke  152  and a plurality of stator teeth  154  extending inwardly from the yoke  152 . Ends of the stator teeth  154  away from the yoke  152  are connected together to form a ring  156 . A plurality of positioning slots  19  is formed in an inner surface of the ring  156 . The provision of the positioning slots  19  makes the rotor  14  stop at a position deviating from a dead point (i.e. a center line of the permanent magnetic pole deviates from a center line of a corresponding stator tooth by an angle) when the stator windings  16  are not energized. Preferably, the number of the teeth and the number of the positioning slots  19  are directly proportional to the number of the rotor permanent magnetic poles, and the stator teeth and the ring are integrally formed and are wound with the stator winding before being assembled to the yoke of the stator core. Alternatively, ends of adjacent stator teeth  154  may be separated from each other by a slot opening. The motor further includes a position sensor  20  ( FIG. 8 ) such as a Hall sensor or a photo sensor. The position sensor  20  is used to sense the position of the rotor. 
         [0039]      FIG. 9  is a block diagram showing a driving circuit  80  of the single phase permanent magnet brushless motor of the present invention. In the driving circuit  80 , the stator windings  16  and an alternating current (AC) power  81  are connected in series between two nodes A and B. The AC power  81  is preferably a commercial AC power supply with a fixed frequency such as 50 Hz or 60 Hz and a supply voltage may be, for example, 110V, 220V or 230V. A controllable bidirectional AC switch  82  is connected between the nodes A and B, in parallel with the series-connected stator windings  16  and AC power  81 . The bidirectional AC switch  82  is preferably a triode AC switch (TRIAC) having two anodes connected to the two nodes A and B, respectively. It should be understood that the controllable bidirectional AC switch  82  may be two silicon control rectifiers reversely connected in parallel, and control circuits may be correspondingly configured to control the two silicon control rectifiers in a preset way. An AC-DC conversion circuit  83  is connected between the two nodes A and B, in parallel with the switch  81 . An AC voltage between the two nodes A and B is converted by the AC-DC conversion circuit  83  into a low voltage DC. The position sensor  20  may be powered by the low voltage DC power outputted from the AC-DC conversion circuit  83 , for detecting the position of the magnetic poles of the permanent magnet rotor  14  of the synchronous motor  10  and outputting corresponding signals. A switch control circuit  85  is connected with the AC-DC conversion circuit  83 , the position sensor  20  and the bidirectional AC switch  82 , and is configured to control the bidirectional switch  82  to switch between a switch-on state and a switch-off state in a predetermined way, based on the magnetic pole position of the permanent magnet rotor and the polarity of the AC power source, such that the stator winding  16  urges the rotor to rotate only in the above-mentioned fixed starting direction during a starting phase of the motor. In this embodiment, in a case that the controllable bidirectional AC switch  82  is switched on, the two nodes A and B are short-circuited, and the AC-DC conversion circuit  83  does not consume electric energy because there is no electrical current flows through the AC-DC conversion circuit  83 , hence, the utilization efficiency of electric energy can be improved significantly. 
         [0040]      FIG. 10  illustrates another type of motor  10  utilized in the above embodiment. The motor  10  is of an outer rotor type, with the rotor  14  disposed surrounding the stator  13 . An uneven air gap is formed between the permanent magnetic poles of the rotor and the stator core. Preferably, the air gap at each of the permanent magnetic poles is symmetrical about a center line of the each of the permanent magnetic poles, and has a radial width gradually increasing from a center toward two ends of the each of the permanent magnetic poles. 
         [0041]    In the present invention, the load  40  may be a fluid generating device with a plurality of blades such as a fan used for bathroom fan, range hood and so on or an impeller used for a pump such as drain pump, circulation pump of a washing machine or dish washer. 
         [0042]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.