Patent Application
20100307399
1. Field of the Invention
The present invention relates to a thread tensioning device for a sewing machine which can provide effective tension timely to the thread during a thread loosening process to avoid the occurrence of skip stitch while effectively improving the sewing quality.
2. Description of the Prior Art
In order to provide a proper amount of tension to the thread while the thread hook loosens the thread, a sewing machine is normally provided with a spring structure which is disposed on the moving path of the thread to keep pressing against the thread. However, the above conventional structure has the following drawbacks: when the thread is pulled, the deformation of the spring is greatly increased, at this movement, the tension is too great, which will produce too much tension on the thread during a thread loosening operation, and thus the thread is likely to be broken. When the thread loosening operation is finished, the deformation of the spring is reduced, but the spring still keeps pressing against the thread with a certain amount of elastic force, so that an elastic tension still exists even when the thread doesn't need tension. As a result of this, when being pulled, the thread will also be broken due to an instant overlarge tension. In addition, although the spring is used to press against the thread to provide tension to it, the tension of the thread is often either too great or too small, so it is difficult to perform the thread hooking operation assuredly during the thread loosening operation, thus causing the occurrence of skip stitch and needing improvement.
Further, when the thread is broken, since one end of the spring is provided with a hook which has poor sealing capability, the thread is likely to disengage from the hook. Further, it is also inconvenient to put it back into the spring once the thread is fallen out of the hook of the spring. Moreover, in order to control the change direction of the elastic force of the spring, the spring must be additionally provided with a framing structure to keep the deformation of the spring in a certain direction, thus inevitably increasing the structure complexity. In some other thread tensioning devices, the spring is totally replaced by a linkage cam, so that when the thread is pulled or loosened, due to the rotation of the cam, the thread can truly and selectively be kept in a tensioned state in a predetermined process and in a non-tensioned state in other processes. This structure is excessively complicated, so not only the production cost is higher, but the maintenance cost is also higher.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.
The primary objective of the present invention is to provide a thread tensioning device for a sewing machine which is disposed on a moving path of the thread of the sewing machine. The thread tensioning device of the present invention is provided with a limit member and a pulling member mounted on the limit member. During a thread loosening operation, with an elastic extension portion and a thread pulling portion of the pulling member, and limit portions disposed on the limit member for limiting the movement of the thread, the thread tensioning device of the present invention can provide a proper amount of tension timely to the thread to allow the thread to be pulled by the thread hook and keep them in the optimal cooperation state, thus improving the sewing quality.
The secondary objective of the present invention is to provide a thread tensioning device for a sewing machine which is simple in structure. The thread tensioning device for a sewing machine is provided with a limit member and an elastic pulling member that cooperate with each other. Since the limit member guides the pulling member to elastically move in a certain direction and limits the travel of the thread, the thread tensioning device for a sewing machine of the present invention which has simple structure can provide effective tension to the thread, thus reducing the production cost.
The third objective of the present invention is to provide a thread tensioning device for a sewing machine which can facilitate installation of the thread by forming an open type thread guide portion on a free end of the limit member in such a manner that the thread can be effectively and quickly placed in a travel limit space defined by the limit member and limited therein.
The present invention will be clearer from the following description when viewed together with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiment in accordance with the present invention.
Referring to
Further referring to
The limit member 31 further includes a rod-shaped guide portion 311, a first limit portion 312, a second limit portion 313 and a thread guide portion 314. The guide portion 311 vertically extends from the fixing portion 310. The extending direction of the guide portion 311 is the same as the moving direction a of the thread 20. The pulling member 32 is mounted on the guide portion 311. The guide portion 311 is inserted through and extends upward out of the pulling member 32 to the top end of the travel path of the thread 20 and is then bent reversely to form the first limit portion 312. As shown in
The pulling member 32 is an extension coil spring and includes a smaller-diameter tightening end 320 with an inner diameter equal to or slightly smaller than an outer diameter of the guide portion 311 in such a manner that the pulling member 32 can be positioned on guide portion 311 by its elastic force. Further, the pulling member 32 can axially move along the guide portion 311 to adjust the tension applied by the pulling member 32 to the thread 20 and to adjust the position at which the thread is to be pulled.
The pulling member 32 further includes a bigger-diameter elastic extension portion 321 extending from the tightening end 320, and a hook-shaped thread pulling portion 322 extending from the elastic extension portion 321 towards the first limit portion 312 and the second limit portion 313 of the limit member 31. Between the elastic extension portion 321 and the guide portion 311 is defined an elastic clearance. The thread pulling portion 322 includes a thread limit end 323 that is bent downwards and straddles the second limit portion 313. The thread limit end 323 is slightly longer than a distance between the first limit portion 312 and the second limit portion 313, so that when the thread pulling portion 322 is pulled by the thread 20 to move between the first limit portion 312 and the second limit portion 313, the thread pulling portion 322 can be ensured to straddle the second limit portion 313, and the thread 20 can be prevented from disengaging from the thread limit end 323 when in a loosened state.
Referring to
When the thread hook 12 of the sewing machine 10 is operated to loosen the thread 20, since the thread pulling portion 322 of the pulling member 32 is slightly higher than the second limit portion 313, the thread 20 can be moved between the first limit portion 312 and the second limit portion 313 without being pulled by the thread pulling portion 322. Therefore, the thread 20 is in the non-tensioned state and can pass through the thread tensioning device 30 quickly without being subjected to any resistance, predetermined fore or pressure. When the thread hook 12 moves right to the position as shown in
Additionally, the pulling member 32 and the limit member 31 of the present invention can also be combined in such a manner as shown in
With the above structure design, the present invention has the following functions:
1. Providing the required tension to the thread 20 substantially: since the tightening end 320 of the pulling member 32 is tightened on the guide portion 311 in such a manner that the pulling member 32 can be axially moved along the guide portion 311 of the limit member 31 to change the position of the thread pulling portion 322 of the pulling member 32, the thread pulling portion 322 can pull the thread if necessary to apply a proper tension to the thread 20 to improve the sewing quality.
2. Convenient to adjust: since the tightening end 320 of the pulling member 32 is elastically tightened on the guide portion 311, the pulling member 32 can be directly moved in an elastic manner, thus achieving the objective of convenient and quick movement.
3. Simple in structure: since the overall structure of the thread tensioning device present invention is fixed through a cooperation of a fixing portion 310 and a fixing member 33, and the pulling member 32 and the limit member 31 are simple in structure and assembled in an engaging manner, the thread tensioning device of the present invention is quick and convenient to assemble.
4. It is quick and simple to install the thread 20: the installation of the thread 20 is finished with only one step that is pulling the thread over the thread limit end 323 without any complicated thread inserting operation.
5. The travel path of the thread 20 can be effectively controlled: the thread 20 is limited by the second limit portion 313, the first limit portion 312 and the thread pulling portion 322 at the same time, so that when being pulled to the highest point of its travel path, the thread 20 will be limited by the first limit portion 312 to keep the tension thereof within a certain range without causing overlarge tension due to excessive pull on the thread 20, thus ensuring an even sewing force and improving the sewing quality.
While we have shown and described various embodiments in accordance with the present invention, it is clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.
