Since the thread bobbin, once stored in a bobbin case (abbreviated as BC in the present invention), rests under the compartment of the sewing machine, the operator is unable to see it during sewing operation. Therefore, faulty stitchings happen due to being unable to see and detect the exhaustion or breakage of lower thread during sewing operation, and results in inferior quality or re-work of sewing operation. As a result, production cost may increase or productivity may decrease. In order to solve such problems, there is a need for an apparatus that detects the situation at which there is only a small amount of lower thread left before being completely exhausted (i.e. the lower thread has reached the ending region), and an apparatus that detects the thread bobbin's rotation in order to determine the situation of the lower thread being broken.
Previous methods used to detect whether the lower thread has reached the ending region and whether the thread bobbin rotates included 1) detecting conductive material painted on the lower thread's ending region, 2) detecting fluorescent material painted on the lower thread's ending region, 3) sticking a light reflective tape or a light polarizing reflective tape to the bobbin core, on which the lower thread is wound, and detecting whether the light illuminated from outside is reflected, 4) sticking a bar code tape to the bobbin core, on which the lower thread is wound, and reading if the bar code once appears, 5) sticking a bobbin rotation detection mark to the bobbin's sidewall flange and determining the change in the rotation direction of the thread bobbin, or 6) sticking a bobbin rotation detection mark to the bobbin's sidewall flange and determining the number of rotations or the rotation speed of the thread bobbin.
For the methods detecting the conductive material or the fluorescent material painted on the lower thread's ending region, some processes such as painting the conductive or fluorescent material on a certain length from the end of the lower thread and drying the material are additionally required to the existing process of winding the lower thread on bobbin cores or bobbins. Therefore, these methods are extremely wasteful in terms of time as well as labor force, and thus, production costs increase while productivity decreases and additional quality related problems occur. Furthermore, these methods do not provide any means of detecting the thread bobbin's rotation in order to determine the situation of the lower thread being broken, and thus, an entirely separate device and mechanism must be additionally used.
The methods sticking a light reflective tape, a light polarizing reflective tape, or a bar code tape (these are collectively termed as reflecting tape hereinafter) to the bobbin core and detecting the light reflected from the reflecting tape, which is exposed when the lower thread is almost exhausted, are nearly impossible to be used for existing sewing machines. This is because there is no space to attach a light emitting unit and a light receiving unit inside the BC, and it is very inconvenient to install the electric wire that delivers the output signal from the light receiving unit to an alerting device outside. Therefore, these light units have to be installed on the front of the BC or the back of the hook device; thus, the light emitting unit must accurately illuminate light at a very steep angle onto the small cylindrical bobbin core (diameter 0.7˜0.8 Cm, length 0.8˜0.9 Cm), which is located at the bobbin spindle inside the BC, through the small hole or space that has been formed on the BC or hook device; and the light receiving unit must be aligned so that it is able to accurately receive the light reflected back from only the bobbin core; these are all very difficult to do in actuality. Specifically, as the BC's interior wall possesses a smooth surface made of a metallic substance, it is very difficult to accurately illuminate light onto the reflective tape attached on the small cylindrical bobbin core and accurately detect the reflected light without scattering of reflection. Furthermore, as severe shaking occurs during the sewing operation, it becomes very difficult for the two light units to remain accurately aligned with the reflective tape attached on the small cylindrical bobbin core. In actuality, if such methods were to be employed, the existing sewing machine structure would have to undergo drastic modification, or the hook device as well as the BC and other numerous existing devices used in the sewing machine must be exchanged with specially designed products, resulting in expensive costs and thus, make them almost impossible to be used for existing sewing machines. In addition, these methods do not provide any means of detecting the thread bobbin's rotation in order to determine the situation of the lower thread being broken.
By the way, the automation process of sticking the reflecting tape to the bobbin core is not only difficult but very expensive in terms of production costs. That is, it is very difficult in actuality to completely automate the process of sticking an extremely small reflective tape one by one to a cylindrical bobbin core made of plastic material; therefore, not only a lot of labor force is required, but also a lot of quality related problems are generated during the process, and results in the production costs being much greater than those of the process using just bobbin core made of plastic material. In addition, as the lower thread has to be wound on the slippery reflecting tape during the thread winding process, the lower thread will be wound unevenly and results in the occurrence of an additional quality related problem.
For the methods attaching a bobbin rotation detection mark on the side of the thread bobbin and detecting the change in the rotation direction of the thread bobbin, a certain length of lower thread from its end must be wound in one direction and then in the opposite direction from there on after during the process of winding lower thread on the bobbin core or bobbin. These methods must not only modify the existing lower thread winding process, in which the lower thread was wound in only one direction, but also exchange all existing machines of winding lower thread, and additionally invoke severe quality related problems that occur as the already wound lower thread unravels during the process of winding in the opposite direction.
The methods attaching a rotation detection mark on the bobbin's sidewall flange and determining the number of rotations or the rotation speed of the thread bobbin are fundamentally unable to accurately detect the ending region of the lower thread. Since, these methods may determine that the lower thread has reached the ending region, even though there is a lot of lower thread left, thus resulting in the waste of a lot of lower thread; or may not even detect it until the lower thread has been completely exhausted. The reasons are that the operator does not maintain a constant motor speed during sewing operation, and that the sudden start or stop of the motor causes false rotations of the thread bobbin located inside the BC; all of which make it difficult to calculate the rotation speed of the thread bobbin, and thus, there is a large margin for error in detecting the lower thread ending region based on calculating rotation speed. Also, the length of lower thread wound on each of the thread bobbin is not the same; thus, there is a large margin for error in determining the lower thread ending region based on counting the number of thread bobbin's rotation. Besides, these methods are not useful for the thread bobbin which doesn't have a sidewall flange. Therefore, these methods cannot support the recent market trend of industrial sewing machines and embroidery machines, a lot of which use the thread bobbins having only the bobbin core.
As reviewed above, previous methods for determining the situation of the lower thread reaching the ending region and the rotation of the thread bobbin have not been used in markets because of many problems: 1) invoke problems in the process of winding the thread on the bobbin core or the bobbin, 2) increase the production costs of the thread bobbins or quality related problems, 3) difficult to apply to existing sewing machines, 4) do not correctly detect the lower thread ending region of the thread bobbin, or 5) do not provide functions detecting the thread bobbin's rotation for determining the situation of the lower thread being broken.