The key factors affecting the operating speed of DFU Ball Screws
DFU cnc machine lead screw speed performance is not determined by a single parameter, but by its own design, external drive, working conditions and other factors, different factors through different mechanisms to affect its actual operating speed limit:
First, the direct constraints of the screw's own design parameters
The synergistic effect of the lead and rotational speed
The linear speed of the screw is jointly determined by the lead (propulsion distance per revolution) and the rotational speed, with the formula v = lead × rotational speed / 60 (v unit: m / s, lead unit: m, rotational speed unit: r / min). The larger the lead, the higher the speed at the same rotational speed -- the speed that can be achieved by a screw with a larger lead at a specific rotational speed requires a screw with a smaller lead at a higher rotational speed to realize. However, if the lead is too large, the rigidity of the screw will be weakened, and it is easy to be "destabilized" due to vibration at high speed, which limits the space for actual speed increase.
Physical limitations of the structure size
The diameter of the screw directly affects the anti-vibration ability: when the small diameter screw rotates at high speed, the centrifugal force is easy to trigger radial oscillation, and the critical speed (the safe speed to avoid resonance) is low; the large diameter screw is more rigid, and the critical speed is higher, which is more suitable for high-speed scenarios. The length of the screw will aggravate its own deflection, and the "flopping" phenomenon is obvious when running at high speed, which not only slows down the speed, but also may lead to abnormal friction between the nut and the screw.
The hidden influence of material and processing precision
High-strength alloy steel after quenching treatment, the deformation resistance is significantly improved, and can withstand greater torque at high speeds; while ordinary steel at high speeds may be due to stress concentration resulting in thread deformation, indirectly limiting the speed. At the same time, the raceway surface of high-precision screws is smoother, the clearance between the nut and the screw is more uniform, the friction resistance is small and less heat is generated when running at high speed, so it can maintain high speed stability compared with low-precision screws.
Second, the drive and transmission system performance matching
drive motor output capacity
servo motor or stepping motor rated speed is the screw speed "ceiling" - if the maximum speed of the motor is only 2000r/min, even if the design of the screw guide to support a higher speed, the actual can not break through this limitation. If the maximum motor speed is only 2000r/min, even if the screw guide is designed to support higher speeds, it is practically impossible to break through this limit. In addition, the motor torque needs to match the load: when the load is too large (e.g. heavy workpieces), the motor may be forced to slow down due to "not being able to carry", or even lose steps, overload protection, and directly reduce the operating speed.
Suitability of nut structure
The ball circulation method of the nut has a significant impact on the high-speed performance: the inner circulation nut (through the reverser to realize ball circulation) is not easy to have ball stagnation at high speed due to the smooth path, which is suitable for the scenario of 3000r/min or above; the outer circulation nut (relying on the curved tube to guide the ball) is prone to ball collision at high speed, which may cause vibration and noise, and the speed is usually limited to 2000r/min or less. The speed is usually limited to 2000r/min or less. At the same time, too much preload will increase the friction between the nut and the screw, and the heat will increase at high speed, so the speed should be reduced to avoid overheating damage.
Third, the working environment and installation conditions of the indirect impact of
load and force state constraints
axial load will make the screw and nut contact stress increases, high-speed operation friction heat increases dramatically, may lead to grease failure or "bite", this time you need to reduce the speed to reduce the heat generated; radial load (such as lateral force caused by installation deviation) will trigger the nut to run. Radial loads (e.g. lateral forces due to mounting deviations) can cause additional moments when the nut is running, and the accumulation of moments at high speeds can exacerbate vibration, forcing the system to slow down to maintain stability. In addition, gravity loads and dynamic load fluctuations (e.g., sudden loading of the workpiece) in vertical drives can also indirectly limit speed by affecting stability.
The safeguarding role of lubrication and heat dissipation
Lack of effective lubrication, the dry friction between the screw and the nut will significantly increase the resistance during high-speed operation, and even trigger local high temperatures; if the grease model does not match (such as low-speed grease for high-speed scenes), it may also be due to insufficient grease mobility to form an "oil film fracture", which will further limit the speed. On the contrary, screws with oil mist lubrication or forced water cooling system can take away the friction heat in time and can run stably at higher speeds.
Hidden limitations of installation accuracy
Installation if the parallelism of the screw and guide rail deviation is too large (such as more than 0.1mm/m), the two ends of the support for different axes, which will lead to the nut running "jamming" phenomenon, high-speed this jamming will be amplified into a violent vibration, not only can not enhance the speed, but also may result in the bending of the screw, the nut wear. In practice, when the installation precision is insufficient, it is often necessary to reduce the speed by more than 30% to ensure the smooth operation of the system.
Fourth, the potential risk of system resonance and rigidity
When the screw rotates at high speed to a specific rotational speed (i.e., critical speed), it may trigger the resonance phenomenon, which is manifested as intense radial vibration, and this vibration, if it continues to occur, will lead to a sudden drop in transmission accuracy, or cause a serious problem.
The critical speed is determined jointly by the rigidity of the material of the screw, the diameter specifications and the length of the screw. The critical speed is determined by the material rigidity, diameter and length of the screw: the screw made of high rigidity material (e.g. steel compared with aluminum alloy) has a higher critical speed; under the same material, the larger the diameter and the shorter the length of the screw, the stronger the resonance resistance is, and the critical speed is also increased accordingly.
In order to avoid the risk of resonance, it is necessary to control the running speed of the ball screw within a reasonable proportion of the critical speed in practical applications, and ensure that it always maintains a stable state during high-speed operation by reserving a safety margin, so as to provide a reliable guarantee for the whole transmission system.
The speed performance of DFU Ball Screws is the result of multiple factors, and needs to be optimized in combination with the load characteristics, precision requirements, environmental conditions, etc. in specific application scenarios, in order to achieve the ideal speed output under the premise of ensuring stability and life.
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