Abstract:
A device for minimizing damage to an electronic article resulting from an overload or jamming of the article that includes a shaft; a driven element carried on the shaft; a clutch plate carried on the shaft; and a torsion spring surrounding a portion of the shaft and having a first end connected to the clutch plate and a second end connected to the driven element such that the spring is windable by a first torque that is greater than a second torque and wherein the second torque produces an operating rotation of the driven element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to motor powered devices and it includes a torsional shock absorber that may be able to prevent or minimize damage from sudden deceleration caused by jamming of the device being driven by the motor. The torsional shock absorbers can be used with hedge trimmers, drills, and other similar motor powered devices.  
         [0002]     One problem with motor powered devices used to power hedge trimmers and the like is that they may become jammed that results in a sudden deceleration that may cause damage to one or more of the parts of the motor powered device. Therefore, it is desirable to provide a means to reduce or prevent damage resulting from the sudden deceleration.  
       SUMMARY  
       [0003]     According to the present invention, a device for minimizing mechanism damage to motor powered article resulting from an overload or jamming of the article includes a torsion spring absorber that includes a driven element, a clutch plate, and a torsion spring connecting the driven element and the clutch plate. The torsion spring is preloaded to that the spring is windable by a first torque that is greater than a second torque and wherein the second torque produces normal functioning of the article.  
         [0004]     Desirably, a shaft is provided to carry the driven element and the clutch plate in a coaxial fashion. The clutch plate is securely connected to the shaft so that it rotates with the shaft. The driven element may be in the form of a gear that is driven by a driving element in the form of a pinion. The driven element is capable of slight relative movement with respect to the clutch plate. As a result, if the driven element is being driven and thus the clutch and shaft are rotating and there is a sudden deceleration causing one of the driven element or the clutch plate to stop, the torsion spring will wind, absorb and dissipate the energy and slow the rotation of the one of the driven element or clutch plate until it stops.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a side view of the torsion shock absorber of the present invention.  
         [0006]      FIG. 2  is a cross sectional view of the absorber shown in  FIG. 1  taken along line  2 - 2 .  
         [0007]      FIG. 3  is a cross sectional view of the absorber shown in  FIG. 1  taken along line  3 - 3 .  
         [0008]      FIG. 4  is a cross sectional view of the absorber shown in  FIG. 1  taken along line  4 - 4  and with the torsion spring removed to better illustrate features of the invention.  
         [0009]      FIG. 5  is a side schematic of another embodiment of the torsion shock absorber of the present invention.  
         [0010]      FIG. 6  is a side schematic of another embodiment of the torsion shock absorber of the present invention. 
     
    
     DESCRIPTION  
       [0011]     Turning now to  FIG. 1 , a torsion shock absorber  10  according to the present invention is shown. The torsion shock absorber  10  includes a driven element  20 , a clutch plate  60 , and a torsion spring  80  connecting the driven element  20  and the clutch plate  60 . The driven element  20  and the clutch plate  60  can be carried by a shaft  50  and can be coaxially aligned with each other.  
         [0012]     The driven element  20  is typically in the form of a gear having teeth  22 , which can be driven by a pinion (not shown) in a conventional manner. The driven element  20  has a first side  24  and a second side  26 . In one embodiment shown in  FIGS. 2, 3 , and  6 , the second side  26  includes an annulus  28  that extends around an inner  30  portion of the driven element  20  to receive a spring  80 , as will be described below. In another embodiment, shown in  FIG. 5 , the second side  26  is simply provided with a cavity  32 . The driven element  20  is held in a suitable axial location by a retaining ring  34  or other securing device on the first side  24  and by the clutch plate  60  on the second side  26 .  
         [0013]     The second side  26  of the driven element  20  has at least one slot  40  and may have two slots. The slot has a first end wall  42  and a second end wall  44 . The slot  40  may be provided on the inner periphery  30  of the driven element. As will become clear when referring to the following description, the slot  40  allows slight relative movement between the driven element  20  and the clutch plate  60 . The slot  20  extends along only a portion of the circumference. In one embodiment, the slot extends along an arc  46  of about 90°, suitably about 45°, and may extend along an arc  46  of about 30°. Where two slots  40  are provided, they will be opposed to each other and will extend along an arc  46  about the same extent.  
         [0014]     As noted above, the torsion shock absorber  10  also includes a clutch plate  60  that can be carried on the shaft  50  coaxially with the driven element  20  and may be carried in any known manner. Suitably, the clutch plate  60  will rotate with and in the same direction as the driven element  20 . Accordingly, the clutch plate  60  is fixed to the shaft  50  in a suitable manner such as by press fitting or welding.  
         [0015]     The clutch plate  60  has a first side  62  and a second side  64  with the second side  64  facing the second side  26  of the driven element  20 . The clutch plate  60  has at least one and may have two tabs  66  that extend from the second side  64  of the clutch plate  60 . The tab  66  extends into the slot  40 . Because the slot  40  extends along a portion of the circumference of the driven element  20 , the driven element  20  can have a slight relative movement with respect to the clutch plate  60 . For example, should a tab  66  be in contact with the first end wall  42  of the slot  40 , the driven element  20  can be rotated in one direction (the counter clockwise direction in  FIG. 4 ) without movement of the clutch plate  60  or shaft  50  until the second end wall  44  of the slot  40  contacts the tab  64 . On the other hand, if the driven element  20  were to be rotated in the other direction (the clockwise direction in  FIG. 4 ), the clutch plate  60  and thus the shaft  50  would rotate with the driven element  20 .  
         [0016]     A torsional spring  80  having a first end  82  and a second end  84  is provided between the driven element  20  and the clutch plate  60 . The torsional spring  80  is wound in a manner such that it surrounds the shaft  50 . In one embodiment, best illustrated in  FIGS. 2 and 6 , the torsional spring  80  is located in the annulus  28  of the driven element  20 . In another embodiment, best seen in  FIG. 5 , where the driven element  20  does not have an annulus  28 , the torsion spring  80  resides in the cavity  32  of the driven element  20 .  
         [0017]     The first end  82  of the torsion spring  80  is connected to a portion of the second side  64  of the clutch plate  60 . The first end  82  of the torsion spring  80  may be connected in any suitable manner such that the first end  82  is securely held to the clutch plate  60 . For example, the first end  82  may be welded to the clutch plate  60  or it may fit into a complementary sized cavity.  
         [0018]     The second end  84  of the torsion spring  80  is connected to a portion of the second side  26  of the driven element  20 . The second end  84  may be connected in any suitable manner such that the second end  84  is securely held to the portion of the driven element  20 .  
         [0019]     In operation, the torsion shock absorber  10  reduces or prevents mechanism damage from sudden deceleration caused by sudden overloads or jamming. The torsion spring  10  is preloaded so that the torque needed to further wind the spring tighter is greater than the normal working load or torque. In other words, after one of the first  42  or second end  44  walls of the slot  40  (depending on the direction of travel) contacts a tab  66  of the clutch plate  60 , the clutch plate  60  will rotate with the driven element  20  under a normal working load or torque and will not be precluded from rotation by the spring  80 .  
         [0020]     When, however, the driven element  20  or the shaft  50  is jammed or rapidly overloaded, the energy stored in the armature (not shown) is transferred to the clutch plate  60 , which winds the spring  80  tighter and thus slows the deceleration of the armature. As a result, the forces on the driven element  20  are dissipated over a longer period of time and damage to the motor, gears, plates, bearings, and other mechanical parts connected to the driven element  20  can be minimized or prevented.  
         [0021]     The deceleration energy is then stored in the torsion spring  80  and the torsion spring  80  will remain in its wound position by the normal stalled torque of the motor because the torsion spring  80  is provided with a spring constant substantially the same as the normal stalled torque of the motor. When the motor is released, the energy stored in the spring will be sufficient to overcome the normal friction of the drive system components and the spring and will then drive the motor in reverse, until it comes to rest. This reverse motion will, in turn, store rotational energy in the armature and as the motor and thus the gearing spins in reverse that motion will act to dislodge the jam.  
         [0022]     Turning now to  FIG. 5 , another embodiment of the present invention is shown. In this embodiment, the clutch plate  60  is provided with has at least one slot  68  and may have two slots in the same manner as described above with respect to the slots provided on the driven element. Accordingly, the slot  68  has a first end wall (not shown) and a second end wall (not shown). The slot  68  extends along only a portion of the circumference. In one embodiment, the slot extends along an arc of about 90°, suitably about 45°, and may extend along an arc of about 30°. Where two slots are provided, they will be opposed to each other and will extend along an arc about the same extent.  
         [0023]     In this embodiment, the driven element  20  is provided with at least one tab  48  and may have two tabs that extend from the second side  26  of the driven element  20 . The tab  48  extends into the slot  68 . Because the slot  68  extends along a portion of the circumference of the driven element  20 , the driven element  20  can have a slight relative movement with respect to the clutch plate  60 , as described above.  
         [0024]     In another embodiment shown in  FIG. 6 , a connecting element  90  is provided with a first end  92  and a second end  94 . The first end  92  or the second end  94  may be secured to one of the driven element  20  or the clutch plate  60 , respectively. Where the first end  92  is secured to the driven element  20 , the clutch plate  60  will be provided with a slot  68  in the same manner as described above so that the second end  94  of the connecting element  90  can travel in the slot  68 . Alternatively, when the second end  94  is secured to the clutch plate  60 , the driven element  20  will be provided with a slot  40  in the same manner as described above so that the first end  92  of the connecting element  90  can travel in the slot  40 .  
         [0025]     Of course, it should be understood that a wide range of changes and modifications could be made to the embodiments described above. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.