Patent Application
20070072686
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.
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.
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.
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.
Turning now to
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
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.
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.
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
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
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.
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.
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.
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.
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.
Turning now to
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.
In another embodiment shown in
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.
