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Ball screw
A ball screw (or ballscrew) is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw. As well as being able to apply or withstand high thrust loads, they can do so with minimum internal friction. They are made to close tolerances and are therefore suitable for high-precision applications. The ball assembly acts as the nut while the threaded shaft is the screw.
In contrast to conventional leadscrews, ball screws tend to be rather bulky, due to the need to have a mechanism to recirculate the balls.
The ball screw was invented independently by H.M. Stevenson and D. Glenn who were issued in 1898 patents 601,451 and 610,044 respectively.
Early precise screwshafts were produced by starting with a low-precision screwshaft, and then lapping the shaft with several spring-loaded nut laps[citation needed]. By rearranging and inverting the nut laps, the lengthwise errors of the nuts and shaft were averaged. Then, the repeatable pitch shaft's pitch is measured against a distance standard. A similar process is sometimes used today to produce reference standard screw shafts and to master manufacturing screw shafts.[citation needed]
Low friction in ball screws yields high mechanical efficiency compared to alternatives. A typical ball screw may be 90 percent efficient, versus 20 to 25 percent efficiency of an Acme lead screw of equal size. Lack of sliding friction between the nut and screw lends itself to extended lifespan of the screw assembly (especially in no-backlash systems), reducing downtime for maintenance and parts replacement, while also decreasing demand for lubrication. This, combined with their overall performance benefits and reduced power requirements, may offset the initial costs of using ball screws.
Ball screws may also reduce or eliminate the backlash common in lead screw and nut combinations. The balls may be preloaded so that there is no "wiggle" between the ball screw and ball nut. This is particularly desirable in applications where the load on the screw varies quickly, such as machine tools.
Because of their high mechanical efficiency, especially compared to traditional lead screws, ball screws can potentially be back-driven (that is, a linear force applied directly to the nut can induce a rotation of the shaft, an effect counterproductive to most uses). While this is usually of limited consequence to motorized applications, and potentially even provides a mild protective effect in some cases, it makes them generally unsuitable for application in manually actuated systems, such as hand-fed machine tools. The static torque and digital control of an appropriate servomotor can be made to resist and compensate, but hand cranked mechanisms would require additional mechanisms to prevent undesirable behaviors. Such undesirable behavior could range from simple loss of control of the machine, such as self-feeding (the tool of the machine causing motion of the axes without the control input of the operator), to potentially dangerous cases where unexpected force could be transmitted all the way to an operator's limbs and pose a risk of injury. Because an ordinary lead screw resists or even prohibits such reverse operation, they are inherently safer and more reliable for manual use. The magnitude of force needed to consequentially back-drive an Acme lead screw would usually be sufficient to destroy the mechanism, immobilizing the machine and absorbing any dangerous force before it could pose a risk to an operator.
The circulating balls travel inside the thread form of the screw and nut, and balls are recirculated through various types of return mechanisms. If the ball nut did not have a return mechanism, then the balls would fall out of the end of the ball nut when they reached the end of the nut. For this reason several different recirculation methods have been developed. An external ballnut employs a stamped tube which picks up balls from the raceway by use of a small pick-up finger. Balls travel inside the tube and are then replaced back into the thread raceway. An internal-button ballnut employs a machined or cast button-style return which allows balls to exit the raceway track and move one thread then reenter the raceway. An endcap return ball nut employs a cap on the end of the ball nut. The cap is machined to pick up balls coming out of the end of the nut and direct them down holes which are bored transversely down the ballnut. The complement cap on the other side of the nut directs balls back into the raceway. The returning balls are not under significant mechanical load and the return path may incorporate injection-moulded low-friction plastic parts.
Hub AI
Ball screw AI simulator
(@Ball screw_simulator)
Ball screw
A ball screw (or ballscrew) is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw. As well as being able to apply or withstand high thrust loads, they can do so with minimum internal friction. They are made to close tolerances and are therefore suitable for high-precision applications. The ball assembly acts as the nut while the threaded shaft is the screw.
In contrast to conventional leadscrews, ball screws tend to be rather bulky, due to the need to have a mechanism to recirculate the balls.
The ball screw was invented independently by H.M. Stevenson and D. Glenn who were issued in 1898 patents 601,451 and 610,044 respectively.
Early precise screwshafts were produced by starting with a low-precision screwshaft, and then lapping the shaft with several spring-loaded nut laps[citation needed]. By rearranging and inverting the nut laps, the lengthwise errors of the nuts and shaft were averaged. Then, the repeatable pitch shaft's pitch is measured against a distance standard. A similar process is sometimes used today to produce reference standard screw shafts and to master manufacturing screw shafts.[citation needed]
Low friction in ball screws yields high mechanical efficiency compared to alternatives. A typical ball screw may be 90 percent efficient, versus 20 to 25 percent efficiency of an Acme lead screw of equal size. Lack of sliding friction between the nut and screw lends itself to extended lifespan of the screw assembly (especially in no-backlash systems), reducing downtime for maintenance and parts replacement, while also decreasing demand for lubrication. This, combined with their overall performance benefits and reduced power requirements, may offset the initial costs of using ball screws.
Ball screws may also reduce or eliminate the backlash common in lead screw and nut combinations. The balls may be preloaded so that there is no "wiggle" between the ball screw and ball nut. This is particularly desirable in applications where the load on the screw varies quickly, such as machine tools.
Because of their high mechanical efficiency, especially compared to traditional lead screws, ball screws can potentially be back-driven (that is, a linear force applied directly to the nut can induce a rotation of the shaft, an effect counterproductive to most uses). While this is usually of limited consequence to motorized applications, and potentially even provides a mild protective effect in some cases, it makes them generally unsuitable for application in manually actuated systems, such as hand-fed machine tools. The static torque and digital control of an appropriate servomotor can be made to resist and compensate, but hand cranked mechanisms would require additional mechanisms to prevent undesirable behaviors. Such undesirable behavior could range from simple loss of control of the machine, such as self-feeding (the tool of the machine causing motion of the axes without the control input of the operator), to potentially dangerous cases where unexpected force could be transmitted all the way to an operator's limbs and pose a risk of injury. Because an ordinary lead screw resists or even prohibits such reverse operation, they are inherently safer and more reliable for manual use. The magnitude of force needed to consequentially back-drive an Acme lead screw would usually be sufficient to destroy the mechanism, immobilizing the machine and absorbing any dangerous force before it could pose a risk to an operator.
The circulating balls travel inside the thread form of the screw and nut, and balls are recirculated through various types of return mechanisms. If the ball nut did not have a return mechanism, then the balls would fall out of the end of the ball nut when they reached the end of the nut. For this reason several different recirculation methods have been developed. An external ballnut employs a stamped tube which picks up balls from the raceway by use of a small pick-up finger. Balls travel inside the tube and are then replaced back into the thread raceway. An internal-button ballnut employs a machined or cast button-style return which allows balls to exit the raceway track and move one thread then reenter the raceway. An endcap return ball nut employs a cap on the end of the ball nut. The cap is machined to pick up balls coming out of the end of the nut and direct them down holes which are bored transversely down the ballnut. The complement cap on the other side of the nut directs balls back into the raceway. The returning balls are not under significant mechanical load and the return path may incorporate injection-moulded low-friction plastic parts.