PM flow controller for guides
You are no doubt familiar with the internal workings of a hydraulic volume controller: a pressure balance, consisting of an unbalanced spring-loaded piston, controls a second flow restrictor so that a constant differential pressure is maintained across the first flow restrictor.
Our PM flow controllers (progressive volume flow controllers) work in the same way with two flow restrictors
The design of the PM flow controller results in the following properties:
- As the flow through the first flow restrictor of the PM flow controller is always laminar, just like the gaps of the hydrostatic pockets, the flow of fluid through the controller and the hydrostatic pockets changes due to the varying fluid viscosity in a similar way. This means that the stiffness and load capacity along with the gap sizes and pocket pressures remain constant, regardless of the fluid viscosity.
If the fluid viscosity changes, e.g., due to differing fluid temperatures or a change of fluid (the permitted viscosity tolerance of an oil grade according to DIN is ± 10%), then the machine properties will hardly be affected. Only the required fluid flow and, to some extent, the damping properties, will change.
- As the fluid flow is only controlled by the elastic deformation of the steel spring disc, i.e., there are no sliding motions, the PM flow controller works without wear or hysteresis. Due to the low mass of the steel spring disc and high regulating forces, the PM flow controller acts very quickly, with natural frequencies many times above the applicable energising frequencies for mechanical engineering. As there are no sliding elements, the controller is also maintenance-free.
- If the supply pressure (=pump pressure) is constant and the hydrostatic pocket load is rising, meaning increasing pocket pressure and therefore outlet pressure on the hydrostatic pocket's controller, the PM flow controller also raises the fluid flow level. This is how four-fold increases in stiffness (!), compared to capillary solutions, are achieved.
The PM flow controller therefore also has the very unusual ability to increase the fluid flow through the controller when the differential pressure on the controller is falling.
Advantages for guides in all applications:
- wear-free, even under maximum load, which means no loss of precision with increasing use
- Power of ten improvement in damping, resulting in considerably better workpiece surface finish and tool service life
- no fluctuations and variations in the friction, as is the case with rolling-element guides due to ball circulation
- no feed force backlash when the direction of motion is reversed
- practically friction-free at low speeds, no stick-slip effect
- capable of travelling less than 0.1 µm
- the sliding properties of the material, slide and guideway are unimportant – moulded mineral, aluminium or casting compound can be used
The hydrostatic guide is adjusted for:
- gravitational, working and accelerating forces
- maximum speed and acceleration as well as the required stiffness and optimum damping