Ball Screw

Ball screws are feed screws that provide high efficiency due to the rolling motion of the balls between the screw shaft and nut.
The drive torque is less than one-third that of a conventional sliding screw, making it ideal for power saving of the drive motor.

Precautions on Use

Types

The ball cage enables this ball screw to have low noise, low torque fluctuation, and long-term maintenance-free operation.

This type of ball screw is mass-produced by cutting the standardized screw shafts of precision ball screws to fixed lengths. Additional machining of the shaft ends can easily be performed.

These ball screw products are fabricated with standardized shaft end shapes. The Model SDA-VZ, which features a compact, ISO-compliant nut, has been added to the lineup.
These products can be used in combination with dedicated support units to make assembly design easy and significantly faster.

The Model BNK is a ball screw with a finished shaft end machined to match the support unit.

This ball screw uses a screw shaft that is ground with high precision.

This is a rotary-nut ball screw that has an integrated structure consisting of a ball screw nut and a support bearing.

The ball screw grooves and the ball spline groove cross one another on a single shaft and the nuts of the ball screw and the ball spline have dedicated support bearings directly embedded on the circumference of the nuts.

This ball screw uses a screw shaft rolled with high precision.

The use of a guide plate system provides a compact design with a round outer diameter for the nut. The screw shaft is roll-molded with a high degree of precision to ensure smooth operation.

The rotary ball screw is a rotary-nut ball screw unit that has an integrated structure consisting of a ball screw nut and a support bearing.

The support unit is available as Models EK, FK, EF, and FF, which are standardized for the standard ball screw assembly provided with the finished shaft ends, and Models BK and BF, which are standardized for ball screws in general. The support unit on the fixed side includes a JIS Class 5-compliant angular bearing provided with an adjusted preload.

The nut bracket is standardized for the standard ball screw assembly provided with finished shaft ends. It is designed to be secured directly on the table with bolts. Since the height is low, it can be mounted on the table only using bolts.

The Lock Nut for the Ball Screws is capable of fastening the screw shaft and the bearing with a high accuracy. The provided hexagonal socket-head setscrew and the set piece prevent the Lock Nut from loosening and ensure firm fastening.

The DSP transmits a large thrust with smooth motion due to the integrated structure of the linear guide ball spline and the ball screw as the drive source.

Features

Driving Torque One Third of the Sliding Screw

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.

Calculating the Lead Angle

β	: Lead angle	(°)
d_P	: Ball center-to-center diameter	(mm)
Ph	: Feed screw lead	(mm)

Relationship between Thrust and Torque

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

Fa	: Thrust generated	(N)
T	: Driving torque	(N･mm)
Ph	: Feed screw lead	(mm)
η1	: Positive efficiency of feed screw	(Driving Torque One-Third That of the Sliding Screw see Fig.1)

● Torque Generated When Thrust is Applied

T	: Torque generated	(N･mm)
Fa	: Thrust generated	(N)
Ph	: Feed screw lead	(mm)
η2	: Reverse efficiency of feed screw	(Driving Torque One-Third That of the Sliding Screw see Fig.2)

Examples of Calculating Driving Torque

When moving an object with a mass of 500 kg using a screw with an effective diameter of 33 mm and a lead length of 10 mm (lead angle: 5°30'), the required torque is obtained as follows.

Rolling guide (= 0.003)
Ball Screw (from = 0.003, = 0.96)

Frictional resistance on the guide surface
Fa=0.003×500×9.8=14.7N

Driving torque

Rolling guide (μ= 0.003)
Ball Screw (from μ= 0.2, η= 0.32)

Frictional resistance on the guide surface
Fa=0.003×500×9.8=14.7N

Driving torque

Ensuring High Accuracy

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.

[Conditions]
Model No.: BIF3205-10RRG0+903LC2

Table1 Lead Accuracy Measurement

Unit: mm

Item	Standard value	Actual measurement
Directional target point	0	-
Representative travel distance error	±0.011	-0.0012
Fluctuation	0.008	0.0017

Capable of Micro Feeding

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.)

High Rigidity without Backlash

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.

Capable of Fast Feed

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

Example of High Speed

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

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