Abstract
Unbalance and vibration of a Japan-made sewing machine (DDW-Type) were studied. Both the needle and its holder of this machine move up and down in its running condition, and therefore they produce unbalane force in its vertical direction. This unbalance force may, however, be cancelled by attaching a certain balance weight to its mainshaft, but by this attached balance weight a new unbalance force may be produced in the horizontal direction. Theoretically we are able to make the total unbalance force completely zero in one direction between the two (vertical and horizontal) directions, but at the same time that in another direction becomes maximum. Therefore, the practical sewing machine of DDW-Type is not made to become the state that the total unbalance force in one direction betw een the two may become zero or maximum in its running condition. This sewing machine has several parts of mechanisms, such as feeding mechanism, which move in only one direction. These parts of course produce unbalance forces in its running condition, but it may be seen from aforesaid facts that they cannot be cancelled by attaching any balance weight to its rotation part. All these unbalance forces in the machine were shown in this paper, and also it was found that in DDW-Type machine, the total unbalance forces are respectively equal to 2550 gr-cm in vertical direction, and 130 gr-cm in horizontal direction.
