| 摘要 |
In a hydraulically-operated traverse motion where the traverse-speed is varied by a driven cam controlling the quantity of pressure-fluid effective to operate the traverse, the cam is movable relatively to the member which drives it and has abutments cooperating with stops to limit the effective surface of the cam. Thus, the programme according to which the fluid-flow is regulated can be kept uniform over a fixed length of each traverse stroke whether the stroke is constant or varies in length, i.e. where the stroke is gradually shortened or increased, or when short strokes alternate with long ones. Two control cams, or a single cam with two control surfaces, may be employed; the cams may be interchangeable and the position of the abutments adjustable for, or during, an operation. In Fig. 1, (not shown), the traverse of a ring-rail is derived from a piston-rod (4) working on a cylinder to one or other side of which pressure-fluid is admitted by a reversing-valve when an arm (7) on the rod contact switches (8, 9) at the end of each stroke. The reversing valve is connected to a pump and an exhaust and communicates with the two ends of the cylinder via throttles (21, 22). These vary the flow-through of fluid per unit of time under the control of cams (35,36), which are on a shaft (25) fixed to a tooth wheel (26) meshing a rack (24) coupled to the piston-rod. Thus for each reciprocation the wheel (26) is rocked to rock the shaft (25) to the same extent for each reciprocation. Since, however, to provide a traverse of uniform length which gradually advances forward, the switches (8,9) are moved gradually (continuously or stepwise) to the left while being maintained at the same distance apart, the return stroke is shorter than the forward stroke and the wheel 26 is gradually indexed forward and shaft (25) is similarly rotated. To ensure that the pattern imposed by the cams on the throttles remains unchanged, the cams are caused to rock only between given limits, whatever the extent of rotation of the shaft. To this end, they are connected to the shaft by a slip-coupling, (Fig. 3, not shown) and have adjustably-mounted abutment members (37, 38, Fig. 2, not shown) engaging fixed stops (39, 391). Thus, with the shaft rotating clockwise, the member (37) is brought against stop (39) and rotation of the cam is brought to a halt, although the shaft continues to rotate; when the travel of the piston is reversed and the shaft rotates anticlockwise, abutment (38) is brought against stop (391) to stop the cam, although the shaft rotates further. When the length of the traverse stroke varies during a wind, during the longest stroke of the traverse, the time in which the cam slips may amount to more than 50% of the duration of the stroke. Arrangements are described where a single cam operates both controls (Fig. 7, not shown), and two abutments are provided on a single member, and where the throttles 21, 22 are coupled with a further regulator adjusted to a constant rate of flow. The cam may take the form of a plate with a curved upper surface and slidably mounted directly on the piston-rod, the sides of the plates acting as abutments engaging adjustable stops to limit the movement of the cam. The cam may be connected to the rod by a plate spring or a magnetic clutch, the latter being released when limit-switches on the sides of the plates engages the stops. |
