Screw fastening device

A screw fastening device comprising a device body from which a stationary base extends frontward, a screw-driving tool arranged in the device body and extending into the stationary base, a guide block threadingly fixed to an inside surface a movable base coupled to and extending outside the stationary base and movable with respect to the stationary base, a positioner fixed to a front end of the movable base, a guide rail extending from a bottom of the movable base, a screw-guiding transmission device arranged at a suitable location inside the movable base, and a guiding and holding device mounted inside the positioner, wherein the curved guide rail extends from the bottom of the movable base, a front surface of the guide rail being recessed and forming a guide chute, which is extended upwardly from a lower end to a chamber defined in the movable base, a strip discharge slot being formed at a suitable location in the chamber to substantially align to the guide chute to allow a screw strip to pass therethrough for assembling and operation, a shaft being arranged at a suitable location inside the chamber for mounting a transmission bar of the screw-guiding transmission device, characterized in that the screw-guiding transmission device comprises the transmission bar, a driving block, a spring, and a peg, wherein the transmission bar forms a threaded hole at a rear portion thereof for threadingly engaging the peg and forms a through hole rotatably fitting over a shaft so that the transmission bar is secured fixed inside the chamber and rotates about the shaft, a front end of the transmission bar being extended to form a pivot portion through which a hole is formed for the extension of a pin for mounting the driving block on opposite sides of the pivot portion, the driving block having a substantially U-shape, comprising two side boards with aligned holes defined in the side boards and corresponding to the hole of the pivot portion, front ends of the two side boards being provided with a projected tooth like configuration, which has an inclined surface at a lower side thereof, to engage engaging slots formed on two side edges of the screw strip, a stop block being formed at a rear portion between the two side boards abuttingly engageable with a bottom surface of a front portion of the transmission bar at a suitable location, the spring being received between inside faces of the two side boards, the spring comprising two coils, a hook being extended from and formed at a front side of each coil, a U-shaped connection being formed between the coils at a rear side thereof and put against at a suitable location on a top surface of the front portion of the transmission bar whereby when the peg moves along the chute of the guide block, the transmission bar is driven, and the front end of the transmission bar is rotated about the shaft to causes the driving block to move up and down and the front ends of the side boards of the driving block engaging the engaging slots on the opposite sides of the screw strip for moving a screw carried on the screw strip into the strip discharge slot to reach a predetermined positioning point, the driving block using a spring force of the spring and rotatable about the pin extending therethrough to have the inclined surfaces at the lower sides of the front ends thereof moving from the engaging slots of the screw strip to next engaging slots and engaging therewith for precise advancing of the screw strip and securely and holding and completely fixing the screw at the positioning point in the strip discharge slot for precise screwing operation of the screw.