1. Field
The present technology relates to mechanisms for feeding and advancing a screwstrip with respect to a power screwdriver.
2. Description of the Related Art
Collated screwstrips are known in which the screws are connected to each other by a retaining strip of flexible plastic material. Such strips are taught, for example, by U.S. Pat. No. 4,167,229, entitled “Screw Strip and Method For Forming The Same,” and U.S. Patent Publication No. 2010/0032326, entitled “Screwstrip With Drive Slots Having Angled Sidewalls,” each of which is incorporated by reference herein in its entirety. Screws carried in such screwstrips are adapted to be successively and incrementally advanced to a position, referred to herein as the target position, in alignment with a bit of a reciprocating, rotating power screwdriver. Once a screw within the strip is properly aligned in the target position, the bit engages the screw and drives it into a workpiece. In the course of the bit engaging a screw and driving it into a workpiece, the screw becomes detached from the plastic strip, leaving the strip as a continuous length.
Known power screwdrivers for driving such collated screwstrips include, for example, U.S. Pat. No. 7,341,146 entitled “Screwdriver With Dual Cam Slot For Collated Screws,” and U.S. Pat. No. 6,164,170, entitled “Semi-Automatic Screwdriver For Collated Screws.” Such known power screwdrivers include a rotatable and reciprocally moving screwdriver shaft which is turned in rotation by an electric motor. A screwdriving bit forms a forwardmost portion of the shaft for engaging the head of each successive screw as each screw is moved into the target position, axially aligned under the screwdriver shaft.
An important aspect of such a power screwdriver is the manner and accuracy with which the screws are advanced and located in the target position. A screw must be properly aligned axially under the screwdriver shaft for successful initial and continued engagement between the bit and the screw head in driving a screw fully down into a workpiece. Screw advance mechanisms are known including a feed lever which engages within slots in the screwstrip to advance the strip in a stepped fashion. Once the feed lever has advanced the screwstrip to its forwardmost position for a given cycle, a screw in the screwstrip is aligned with the screwdriver head and the screw is inserted by the screwdriver into the workpiece. Thereafter, the feed lever moves rearward to engage the next slot in the screwstrip to advance the screwstrip to position the next screw for insertion.
One problem which exists with conventional screw advance mechanisms for use with flexible screwstrips is the ability to accurately position the respective screws in the target position. Occasionally the advance mechanism will under or overfeed the strip resulting in a misalignment of the screw bit with the next screw to be driven. It may also happen that a misaligned screw will be skipped altogether. In addition to alignment problems, it is often difficult to load a screwstrip into the screwdriver and advance it to a position where screws are ready for insertion.