Control of hydraulic actuating cylinders in roll stands

A hydraulic control loop (1) for controlling a hydraulic actuating cylinder (3),

• the hydraulic actuating cylinder (3) having a cylindrical housing (31) and a piston (32) displaceably arranged therein,
• the piston (32) dividing the cylindrical housing interior into a first hydraulic chamber (34) and a second hydraulic chamber (35),
• wherein the hydraulic control loop (1) comprises:
• a first hydraulic valve (10), which is configured to supply the first hydraulic chamber (34) with a hydraulic fluid, wherein a hydraulic pressure of the first hydraulic chamber (34) is adjustable via a control of the first hydraulic valve (10);
• a second hydraulic valve (11), which is configured to supply the second hydraulic chamber (35) with a hydraulic fluid, wherein a hydraulic pressure of the second hydraulic chamber (35) is adjustable via a control of the second hydraulic valve (11);
• and
• a control device (12-20) that is provided for controlling the first hydraulic valve (10) and the second hydraulic valve (11) and is configured
• to control, in a position control state, the second hydraulic valve (11) with a position control signal dependent on a working position of the piston (32) and
• to control the first hydraulic valve (10) with an adjusted position control signal, which is a signal generated based on the position control signal,
• wherein the control device (12-20) includes a switching device (16), which is configured to switch between the position control state and a pressure control state,
• wherein, in the pressure control state for positioning the piston (32), the first hydraulic valve (10) is controlled by the control device (12-20), such that the hydraulic pressure in the first hydraulic chamber (34) remains essentially constant, while the second hydraulic valve (11), controlled by the position control signal, functions as an actuator.