Machine Design

Variable-Stroke Drives

Variable-stroke drives are most widely used in low-speed applications below 1.5 hp. They compete mainly with belt and chain drives and have running efficiencies near 80%. However, unlike belts, variable-stroke drives operate effectively at near-zero output speed.

Speed output is continuously variable from zero to one-fourth input speed. Speeds are maintained and repeated within 1% of maximum in the upper 90% of the range, on the condition that output load and input speed are constant.

Because they are positively coupled devices, basic variable-stroke drives do not slip and, therefore, do not provide overload protection. Thus, variable-stroke drives are usually conservatively rated to provide a large safety factor. Some models have built-in mechanisms that slip at overload before the drive is damaged. These overload devices are not designed for continuous duty, but rather for occasional protection against overload. In most models, the disconnect point is substantially higher than the drive rating, and the reconnect point is at or near the torque rating.

Most variable-stroke drives have a control handle that can be actuated manually or hooked mechanically, pneumatically, or electrically to the controlled machine.

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