Machine Design

Hydraulic Speed Control

When using industrial equipment such as automated drill heads, positioning slides, and transfer conveyors, precise speed and feed control are required more often than not.

While there are a number of options for precise control, probably the most cost effective is the Hydraulic Speed Control. HSCs are linear-acting devices that precisely regulate displacement versus time. Specifically, a load applied to the HSC's piston rod is maintained at a constant speed throughout the entire compression stroke.

HSCs, like shock absorbers, transform kinetic energy into heat by means of hydraulic orificing. However, the significant difference between the two is that HSCs are not intended to absorb the impact velocity of a moving object, but rather control the speed.

As the piston rod travels through the stroke of the HSC, oil is precisely metered through a series orifice. This ensures constant speed over the entire stroke. A pressurized diaphragm accumulator and spring-loaded check valve in the piston head prevent free travel during initial displacement of the rod. The diaphragm is sealed on the piston rod and diaphragm retainer, and a special antirotation device ensures diaphragm rolling action and seal integrity.

The piston-rod assembly returns when the load on the rod is released. A spring acts on the diaphragm to create internal hydraulic pressure, and oil passes through return-flow holes and unseats the check valve. Because internal pressure acts on a larger area of the piston side, compared to the rod side, the resulting force differential rapidly repositions the assembly.

HSCs accommodate exact application needs with wide-range adjustability, multiple speed rates, consistent performance over wide temperature ranges, and a variety of stroke lengths. Because of these qualities, they have been successfully applied on pneumatic slides, robots, drill heads, and woodworking machinery.

Although small in size, HSCs handle up to 1,200 lb of propelling force and regulate speeds ranging from 0.04 to 14 ips. They are typically mounted in one of two ways. For low propelling forces, retaining rings secure the device in a through-hole. When faced with high forces, a mounting block accessory attaches to the HSC and bolts to a flat surface.

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