1. Field of the Invention
This invention relates to a wire saw, and more particularly to a wire saw having a reciprocating wire array made by looping a single wire, so as to cut a work piece urged against the wire array.
2. Description of the Prior Art
A wire saw using a single extended wire to be longitudinally reciprocatingly moved is known. For instance, U.S. Pat. No. 3,155,087, which was granted to Bertrand A. Dreyfus on Nov. 3, 1964, discloses a machine for sawing samples of brittle materials, which machine comprises a wire extending from a feeding roller to a receiver roller while being turned a number of times around wire guides so as to form a material-cutting wire array, a driving means for positively rotating one of said wire guides in forward and reverse directions for reciprocating the wire in said wire array, and a toggle arrangement for preventing the wire from slackening during the reciprocation. The feeding roller of this machine is connected to a control motor for continuously paying a selected amount of fresh wire, while the receiver roller is mounted to a constant torque motor which drives the receiver roller under the control of a control means, so as to receive the payed amount of the wire while causing a constant tension therein and absorbing the elongation of the wire. Thus, such an arrangement provides a continuous renewal of the wire in the array.
The wire saw of the Dreyfus Patent has a drawback in that its control means of the constant torque type should be adjusted very accurately with extra care, because if the receiver roller rotates too quickly, the wire may be cut off by excessive tension. On the other hand, if the receiver roller rotates too slowly, the wire may be slackened. The slackening may also cause the wire to inaccurately cut the work piece.
The wire saw of the Dreyfus Patent also uses a constant torque reversible motor with an armature directly connected to the driving wire guides, as a means for reciprocating the wire in the wire array. The direction of rotation of the reversible motor is controlled by a limit switch to be actuated by the foresaid toggle arrangement. The constant torque reversible motor is rather expensive, and the limit switch controlling such motor requires frequent replacements because of its comparatively short service life. According to the experience of the inventor of the present application, slipping is caused at the joint between the output shaft of the constant torque reversible motor and the driving wire guide or at a point between the driving wire guide and the wire array, although the reason for such slipping has not yet been found.
Therefore, the object of the present invention is to mitigate the aforesaid difficulties of the conventional wire saw.