Stiffness of actuators

The spring effect of the compressed oil column is decisive for the stiffness of actuators. The dimensions of the actuator also play a role.

In the case of a hydraulic motor with a high response proportional valve, the stiffness ("torsional stiffness") is a function of the displacement volume V 2 and the enclosed volume of liquid V 0 on one side:

with E ‘ = compression module.

The symmetrical conditions and small volume of enclosed liquid (if the valve is fitted directly on the motor), give the hydraulic motor more stiffness than the cylinder, but the leakage losses are also greater.

In the case of the hydraulic cylinder, the stiffness is a function of the piston and rod surface area, the stroke and the volume of liquid enclosed in the pipelines.

In the case of a synchronizing cylinder with a high response proportional valve, the minimum stiffness is located in the middle position of the piston:

with V = volume under pressure, A R = annular area in the cylinder. In the case of the differential cylinder there is an additional factor – the influence of the ratio of the piston surface area to the annular area:

with A K = piston surface area.

Cylinders with a large active area and small stroke can be very stiff. In the case of high pressures and strokes, however, they are softer. Stiffness is therefore also a design issue.