Non-Contact Hydrostatic Fluid Bearings
How Non-Contact Hydrostatic Fluid Bearings Work
Non-Contact Hydrostatic bearings are dissimilar to other bearing technologies in that they support loads via a thin layer of pressurized gas instead of a mechanical connection as is done in roller bearings, slide bearings, and journal bearings. The fluid is externally pressurized and forced through a porous medium into a small gap between two bearing surfaces. The fluid viscosity resists this flow to create a stable pressure barrier that rigidly holds the two surfaces apart from one another at a fixed distance.
High Accuracy, Precision, and Repeatability
Hydrostatic fluid bearings are used in machinery tools where precision, accuracy, and repeatability are paramount. This includes extremely high precision CNC machines, Coordinate Measurement Machines and positioning systems used in the aerospace and semiconductor industries. There are several mechanisms by which the accuracy, precision, and repeatability are enhanced with hydrostatic bearings.
The main function of almost all bearings is to constrain the relative motion between two surfaces to a single direction. If the bearing allows movement in an off direction (a direction in which motion should be inhibited) then it is considered to be a poor bearing for the intended application.
Hydrostatic bearings exhibit exceptionally high stiffness when compared to other off the shelf bearing technologies such as wheel in groove, sliding, or recirculating ball bearings. This means that the motion system will move only in the intended directions, increasing the quality of laser cutting, engraving, and marking.
The thin layer of flowing fluid between the bearing surfaces creates an unusually low friction interface with almost zero bearing hysteresis. This allows the system to move freely around the processing area without the mechanical drag associated with other bearing technologies. A specific type of friction known as dry or static friction causes drag when relative motion stops and starts again and is particularly troublesome during laser material processing. Hydrostatic bearings almost entirely eliminate this type of friction resulting in nearly perfect vector motion which increases the quality of both laser cutting and laser engraving.
There are several types of vibrations that can exist within a laser cutting, engraving, and marking machine, and it is critical that these vibration be attenuated as much as possible to ensure high accuracy, precision, and repeatability. Hydrostatic bearings excel at this function – providing some of the best vibration dampening characteristics of any bearing technology. For laser material processing, this means that the motion will be smooth, vibration free, and without any of the characteristic ‘ringing’ defects found in high throughput vector processes.
Other bearing technologies also have a tendency to create self-excited vibration as they move at higher speeds. This is analogous to a misbalanced car tire oscillating as it travels at highway speeds. Hydrostatic bearings do not exhibit this behavior and can maintain high speeds without self-exciting vibrations. This is particularly advantageous in raster mode applications where high speed marks are placed in proximity to one another – exacerbating any oscillations caused by carriage movement.
Exceptional Durability and Longevity
The non-contact nature of hydrostatic bearings is highly advantageous to customers because it provides consistent, high quality results with very little maintenance. This is accomplished in several ways discussed below.
No Mechanical Wear
The fluid moving between the bearing interfaces creates a small, controlled, gap ensuring that the two surfaces never come into contact with one another. This allows the bearing to exhibit extremely long life – well beyond that of other bearing technologies. As the surfaces rub against one another in roller, ball, slide, bearings, the surfaces will wear over time. In the context of laser material processing, wear can occur at accelerated rates because processing byproducts can adhere to the bearing interfaces. Excessive mechanical wear can cause a variety of processing defects or, if left untreated, total laser system failure.
No Lubrication Required
Hydrostatic bearings have no moving parts and therefore do not require lubrication of any kind; grease, oil, etc. From a maintenance perspective, this is a large advantage to the customer. Mechanical contact bearings come in two types: sealed and unsealed. With unsealed mechanical contact bearings, such as the linear bearings used in many laser systems from other manufacturers, there must be regularly scheduled maintenance to ensure that there is adequate lubrication – a process which can be error prone and quite messy. The byproducts of laser material processing will also tend to adhere to lubricated surfaces. Over time this buildup can actually decrease the lifetime of mechanical contact bearings by accelerating abrasion along mating surfaces. For sealed roller bearings such as those used in other ULS laser systems (VLS, PLS, and ILS), no maintenance of lubricants is required, but bearings do wear out and are considered a consumable.
Another distinct advantage of hydrostatic bearings is that the escaping gases serve as a self-cleaning mechanism, clearing off dust and debris along the bearing surface. This feature is especially relevant to laser systems because laser material modification can produce a wide range of byproducts which may adversely affect bearing performance or lead to foreshortened service life.