BLW DK WHF BLK SBN-V SBK SBKN SDAN-V SDA-V Ball Screw THK

With the Ball Screw, balls roll between the screw shaft and the nut to achieve high efficiency. Its required driving torque is only one third of the conventional sliding screw. (See Fig.1 and Fig.2 .) As a result, it is capable of not only converting rotational motion to straight motion, but also converting straight motion to rotational motion.

The torque or thrust generated when thrust or torque is applied is obtained from equations (1) to (3).

● Driving Torque Required to Gain Thrust

T	: Driving torque	(N･mm)
Fa	: Frictional coefficient of the guide surface	(N)
Fa=μ×mg
μ	: Frictional coefficient of the guide surface
g	: Gravitational acceleration	(9.8m/s2)
m	: Mass of the transferred object	(kg)
Ph	: Feed screw lead	(mm)
η1	: Positive efficiency of feed screw	(Driving Torque One-Third That of the Sliding Screw see Fig.1)

● Thrust Generated When Torque is Applied

● Torque Generated When Thrust is Applied

The Ball Screw is ground with the highest-level facilities and equipment at a strictly temperaturecontrolled factory, Its accuracy is assured under a thorough quality control system that covers assembly to inspection.

The Ball Screw requires a minimal starting torque due to its rolling motion, and does not cause a slip, which is inevitable with a sliding motion. Therefore, it is capable of an accurate micro feeding.Fig.4 shows a travel distance of the Ball Screw in one-pulse, 0.1-m feeding. (LM Guide is used for the guide surface.)

Since the Ball Screw is capable of receiving a preload, the axial clearance can be reduced to below zero and the high rigidity is achieved because of the preload. In Fig.5 , when an axial load is applied in the positive (+) direction, the table is displaced in the same (+) direction. When an axial load is provided in the reverse (-) direction, the table is displaced in the same (-) direction. Fig.6 shows the relationship between the axial load and the axial displacement. As indicated in Fig.6 , as the direction of the axial load changes, the axial clearance occurs as a displacement. Additionally, when the Ball Screw is provided with a preload, it gains a higher rigidity and a smaller axial displacement than a zero clearance in the axial direction.

Since the Ball Screw is highly efficient and generates little heat, it is capable of a fast feed.

Fig.7 shows a speed diagram for a large lead rolled Ball Screw operating at 2 m/s.

[Conditions]

Item	Description
Sample	Large Lead Rolled Ball Screw WTF3060 (Shaft diameter: 30mm; lead: 60mm)
Maximum speed	2m/s (Ball Screw rotational speed: 2,000 min-1)
Guide surface	LM Guide model SR25W