relation to said rope guide roller 21 and said intersection of said angles 19 and 20 of said roller support frame 12 each of the control drive cylinders 22 and 23 are comprises of an annular cylinder body member 24 best seen in fig3 and 4 of the drawings an elongated opening is formed at 25 along one side of said cylinder body member 24 with a slit flexible sealing band 26 within said opening a piston 27 is positioned within said cylinder body member 24 and has resilient plastic seals 28 at either end thereof for sealing relation with the interior of said cylinder body 24 the piston 27 has an upstanding elongated apertured drive bracket 29 extending therefrom and through the slit at 25 in the flexible sealing band 26 the control cylinders 22 and 23 hereinbefore described are available on the open market as a origa cylinder series 200 manufactured by origa corporation of 928 north oakland avenue elmhurst ill 60126 and accordingly no further explanation or description of same is required the origa cylinders are fluid driven by a source of fluid pressure not shown via fluid supply inlet fittings 30 and 31 and associated lines 30l and 31l the inlet fittings 30 and 31 are positioned within end fittings 32 in each of the cylinders 22 and 23 the independent control of the aforementioned cylinders 22 and 23 is provided by a control timing.