HOME > Product > Ball Screw > Ball Screw Technical Description > Accuracy Selection

Among the factors the cause feed accuracy errors,lead stroke accuracy and feed system rigidity are the key points for review,while other factors such as heat deformation due to temperature rise as well as assembly accuracy for the guiding surface,etc.should also be taken into consideration.

Accuracy Selection

Table 3.7 shows the recommended application ranges for various ball screws accuracy classes based on different.
Application Shaft Precision Grade
C0
C1
C2
C3
C5
C7
C10
NC Machine Tolls Lathe X
o
o
o
o
o
o
-
Z
-
-
-
o
o
o
-
Milling Machine Boring Machine XY
-
o
o
o
o
o
-
Z
-
-
o
o
o
o
-
Mahining Center XY
-
o
o
o
o
-
-
Z
-
-
o
o
o
-
-
Jig Borer XY
o
o
-
-
-
-
-
Z
o
o
-
-
-
-
-
Drilling Machine XY
-
-
-
o
o
o
-
Z
-
-
-
-
o
o
-
Grinding Machine X
o
o
o
o
o
o
-
Z
-
o
o
o
o
o
-
Electro-discharge machine XY
-
o
o
o
o
o
-
(Z)
-
-
o
o
o
o
-
Wire Cut XY
-
o
o
o
-
-
-
UV
-
o
o
o
o
o
-
Punching Press XY
-
-
-
o
o
o
-
Laser Cutting Mahine XY
-
-
-
o
o
-
-
Z
-
-
-
o
o
o
o
Wood Working Machine
-
-
-
o
o
o
o
Machines of General Use and Special Use
-
-
o
o
o
o
o
Semiconductor Mahchine Explosure Equipments
o
o
-
-
-
-
-
Chemical Treatment
-
-
-
o
o
o
o
Wire Bonder
-
o
o
o
-
-
-
Prober
o
o
o
o
-
-
-
Inserter
-
-
o
o
o
o
-
PCB Driller
-
o
o
o
o
o
-
Industrial Robots Orthogonal Type As'sy
-
o
o
o
o
o
-
Others
-
-
-
-
o
o
o
Multi-Joints Type As'sy
-
-
o
o
o
-
-
Others
-
-
-
o
o
o
-
SCARA Type
-
-
o
o
o
o
-
Machines for Steel Molding
-
-
-
-
o
o
o
Injuction Molding Machine
-
-
-
-
o
o
o
Three-Dimensional Measuring Machine
o
o
o
-
-
-
-
Business Machine
-
-
-
-
o
o
o
Pattern Image Machines
o
o
-
-
-
-
-
Nuclear Rod Control
-
-
-
o
o
o
-
Mechnaical Snubber
-
-
-
-
-
o
o
Aircrafts
-
-
-
o
o
-
-

Countermeasure Against Thermal Displacement

Thermal displacement of the screw shaft results in deterioration of the positioning accuracy.The magnitude of the thermal displacement is calculated as follows:
= • t •L (mm)
: Thermal displacement (mm)
t: Temperature rise (deg) at screw shaft
L: Screw shaft length (mm)
: Coefficient of thermal expansion (11.7 x 10-6deg-1)

Namely, the screw shaft develops elongation of 12£gm per 1m when the temperature rises by 1°C. The ball screw, which lead has been machined to high accuracy, may fail to meet highlevel requirements because of the thermal displacement due to temperature rise.As the ball screw is operated at higher speeds,the heat generation grows to increase the influence of temperature rise.

The thermal displacement countermeasures for ball screws include the following:
(1) Control of heat generation
Optimization of preload
Correct selection and supply of lubricant
Increase in ball screw lead,with reduced rotation speed
(2)Forced Cooling
Hollow screw shaft to allow cooling fluid to flow through
Cooling of screw shaft exterior with cooling oil or air
(3) Avoid influence of temperature rise
High-speed warming up for use in a temperature stabilized size
Pre-tension of screw shaft
Negative travel compensation of cumulative lead
Use of closed loop