During use of common hand tools such as screwdrivers and torque wrenches, there is a movement limitation of the human hand when rotating; more specifically, the inability of the human hand to turn continuously in one direction. The operation of such a tool, which a rotation axis of the handle is coaxial with the tool's main shaft comprises a repetition of the following cycle: first, the hand rotates the handle in the desirable direction (e.g., tightening or loosening a screw); second, the hand rotates in the opposite direction to reposition the tool for the next cycle. During the second portion of the above mentioned cycle, the hand's reversed rotation can be achieved by re-grasping the handle after releasing it, by the tool if it is equipped with a one-way means such as a ratchet surface to keep the main shaft stationary during the reversed rotation of the handle, or by re-inserting the tool bit to the screw after extracting the bit from engagement with the screw. However, in any case, the hand's reversed rotation could not bring any effective advance of the fastener, and therefore it becomes a wasted movement.
U.S. Pat. No. 5,931,062 discloses a mechanical rectifier, which comprises a shaft; two driving elements mounted on the shaft, each having a one-way clutch interposed between it and the shaft, with the clutches oriented in the same way on the shaft so that the shaft is always entrained in only one direction of rotation when either one of the two driving elements is rotated in that direction, and the shaft is overrun by a driving element that is rotated in the opposite direction; a rotation means positioned along the axis of the shaft and engaging a selected one of the driving elements; and a reversing mechanism coupling the two driving elements together and forcing them to always rotate in opposite directions so that one driving element entrains the shaft and the other driving element overruns the shaft, thus causing the shaft to always turn in only one direction regardless of the direction of rotation of the driving elements, so the bidirectional rotation of the rotation means (e.g., a handle) transfers into the unidirectional rotation of the shaft. The mechanical rectifier can efficiently utilize the rotations of the rotation means in either way; whether the handle rotates clockwise or counterclockwise, the shaft rotates in the same direction, therefore it can improve the efficiency of the hand motion, and save operation time.
However, the converting mechanism of the invention can only make the shaft rotate in one direction, which does not allow the rotation of the shaft in two directions. Tightening or loosening a fastener with a torque wrench equipped with the converting mechanism of the invention could only get the result of tightening a fastener (or loosening a fastener) no matter what operation it executes—either tightening or loosening a fastener as the conventional wrenches do. For a torque wrench equipped with the converting mechanism of the invention to execute the operation of tightening and loosening a fastener, the two ends of the shaft of the torque wrench are both engageable with the rotational output, and one end is to execute the operation of tightening a fastener, the other to execute the operation of loosening a fastener. But this design is cumbersome, it is inconvenient to choose the appropriate output end when using the torque wrench.
Therefore, it is desired to develop a bidirectional wrench, which is capable of switching the rotation direction of the shaft conveniently.