There is a lot of jargon related to ballscrews, some familiar and some less so. Ballscrews suppliers don’t often explain what it all means so here we will run through a few of the terms associated with these products that you should know if you have any dealings with applications using ballscrews.
Backdrive, Backlash and Creep
Backdrive refers to the action of converting thrust motion back into torque motion. It can reduce the efficiency of an application, though its effect can be reduced with a self-locking mechanism. Backlash refers to the movement of a screw and nut from its original position. Creep is similar to backlash, but is caused by the vibrations and shocks from heavy loads, whereas backlash is not caused by such vibrations.
Critical Speed and Speed
The critical speed of revolving screw shafts refers to the frequency speed of vibrations caused by the screws’ revolutions. The frequency of the generated vibration will depend on the size and shape of the screw shafts.
Speed is the measurement of the speed of linear movement within ballscrew assemblies, usually measured by RPM (revolutions per minute).
How the ends of each screw is supported is called end fixity. The three most common types of end fixity are free, supported and fixed. The end fixity of a screw is a crucial part of screw and nut drive systems. The screw end’s rigidity will determine how much resistance to column buckling there is and how limitation is placed on the rotational speed of the screw drive system. The different types of end fixity has a significant bearing on natural frequency vibrations.
Ballscrew assemblies using continuous screw rotation without linear movement are known as freewheeling. Freewheeling ballscrews differ from traditional ballscrews in that the balls are arranged and contained within the nut housing. Instead of re-circulating the balls back to the opposite side of the nut, the balls of a freewheeling ballscrew continuously re-circulate throughout the nut housing.
The energy generated between a screw and its nut is friction, or resistance to movement. There are different types of friction, with ballscrews typically creating a rolling friction. There is also the sliding friction generated by many lead screws and ACME screws in particular.
Pitch refers to the axial measurement between the threads of ballscrews, though it can also refer to the amount of full rotations a screw makes in order to produce a particular measurement of movement betwixt the nut along its screw.
Shafts and Threads
The shaft is the part of the screw that contains the threads, while the threads are the raised helical rib that goes around the screw’s shaft.
Stroke, Thrust and Torque
Stroke is the measurement of a ballscrew system’s linear motion or thrust, with the thrust itself being the linear movement created by the torque produced from ballscrew assemblies. Torque refers to the rotational movement of a ballscrew system that converts into thrust.If you require any of the products resulting from ballscrews manufacture – then contact YB Components who are the UK’s leading ballscrews suppliers