This invention relates to vibratory concrete screeds and in particular to a device for automatically driving a portable screed at various propulsion speeds as the screed imparts uniform vibrations to poured concrete for tamping and levelling of the concrete as it is finished.
As related in my co-pending U.S. patent application, Ser. No. 234,348, filed Feb. 13, 1981, as labor costs continue to escalate in the building industry, builders increasingly have turned to machines which accomplish labor-intensive tasks in the least possible time in order to incur the least possible labor expense. The above-identified application, which is incorporated herein by reference, discloses an improved vibratory concrete screed which, when propelled across a freshly-poured concrete surface, automatically tamps and levels the concrete to a finished surface.
Although the concrete screed of the above-identified pending application substantially increases the productivity of concrete finishing, the screed itself is driven manually by means of a hand-cranked winch. Thus, an operator must constantly monitor the screed and continually wind the winch in order to advance the concrete screed across the concrete. Since advancement of the concrete screed depends upon the operator, and since a human operator can rarely advance the concrete screed with any degree of uniform regularity, an inexperienced operator may advance the concrete screed too fast or too slow, thus either requiring another pass across the concrete to properly finish it, or taking too much time to traverse the poured concrete. In either case, greater time than required to adequately complete the job is expended, increasing costs.