Aluminium beam air bearing costs a fifth of granite system

Dean Palmer reports on a new aluminium beamed air bearing which is suitable for high throughput, low maintenance production environments A company has developed an extruded aluminium beam that creates a platform for air bearing linear motion and which looks ideally suited to high throughput manufacturing industries such as digital printing, semiconductors, electronics and bio-medical production - and it costs around a fifth of a granite beam equivalent. While the developer, Anorad (part of Rockwell Automation) will not divulge precise details of the aluminium beam construction, it says the system involves "specific ribbing and webbing geometry". The resulting design creates an easy-to-manufacture air bearing that delivers sufficient rigidity and stiffness to attain repeatability in the order of a few microns, velocity stability of less than 1% deviation and the system can carry a payload of up to 15kg at 3m/s with 2G acceleration. Anorad has a wealth of experience in manufacturing high accuracy granite beamed linear axes and therefore understands the problem of small, trapped particles of dirt eroding the surface of the beam in production. So the new aluminium beam design incorporates a puck that is slightly porous, allowing any trapped particles to be absorbed into the pores. The air cushion that the puck rides on also assists in clearing away particles from the bearing surfaces. The linear motor itself has an epoxy core (ironless) design and feedback accuracy comes from a linear optical encoder. Good bearing preload provides stability and stiffness and, because the linear motors are commutated as a brushless servo motor, any number of amplifiers and motion controllers are compatible with it. According to Andy Holmes, applications engineer at Anorad, "Other benefits of the system include high throughput, high accuracy and repeatability, low current consumption, exceptional velocity control and easy fixing." The other great thing is the cost of the system. Holmes said a granite air beam system typically costs around £50k but the two-metre long aluminium beam system costs only about one-fifth of this.