Technical Calculation Software
| File Name | Catalog Page | File Size | Uncompressed File Size |
|---|---|---|---|
| Linear Guides · Ball Screws Technical Calculation Software Ver.2.0 | - | 6.79 MB | 6.85MB |
Ball Screw Lead Accuracy
Ball screw accuracy is defined by JIS Standards (ep, vu, v300,v2?).
Definitions and allowable values for the terms are shown below. In general, the ball screw accuracy grade selection is made by confirming that the required positioning accuracy is within the screw's Actual Mean Travel Error value.
Table 1. Allowable values for Positioning Screws (C series) Actual Mean Travel Error (±ep) and Variation (Vu) .
Unit: μm
| Effective Thread Length (mm) |
Accuracy Grade | ||||
|---|---|---|---|---|---|
| C3 | C5 | ||||
| over | less than | Actual Mean Travel Error | Variation | Actual Mean Travel Error | Variation |
| 315 400 500 630 800 1000 1250 |
315 400 500 630 800 1000 1250 1600 |
12 13 15 16 18 21 24 29 |
8 10 10 12 13 15 16 18 |
23 25 27 30 35 40 46 54 |
18 20 20 23 25 27 30 35 |
Table 2. Allowable values for Positioning Screws (C series) Variation Per 300mm (v300), and Variation Per 1 Rotation
Unit: μm
| Accuracy Grade | C3 | C5 | ||
|---|---|---|---|---|
| Item | V300 | v2? | V300 | v2? |
| Standard Value | 8 | 6 | 18 | 8 |
Table 3. Allowable values for Transfer Screws (Ct series) Variation Per 300mm
Unit: μm
| Accuracy Grade | Ct7 | Ct10 |
|---|---|---|
| V300 | 52 | 210 |
[ ! ] Actual Mean Travel Error (ep) for Transfer Screws (Ct series) is calculated by ep = 2 · Lu/300 · V300.
| Glossary | Symbol | Meaning |
|---|---|---|
| Actual Mean Travel Error | ep | Value derived by subtracting Specified Travel from Actual Mean Travel |
| Variations | Vµ V300 v2? |
|
| Specified Travel | ls | Axial travel corrected against Nominal Travel (lo) for temp.and load variations. |
| Specified Travel Target Value | t | A value by subtracting Nominal Travel from Specified Travel within the effective thread length. This is set by compensating for contraction and expansion of the screw shaft due to temp. changes. The value is determined by experiments or experiences. |
| Actual Travel | la | Actually measured travel |
| Actual Mean Travel | lm | A straight line representing the trend of actual travel. It is obtained by the least-squares method or an approximation similar using the curve representing the actual travel. |
Ball Screw Backlash
Backlash does not affect the accuracy of positioning when feeding in one direction only, but will generate a backlash and affect positioning accuracy if the feed direction or the load are reversed. Select a proper backlash according to the required level of accuracy.
Table 4. Backlash of Rolled Ball Screws
| Type | Representative Type | Screw Shaft Diameter | Lead | Backlash (mm) |
|---|---|---|---|---|
| Standard Nut Accuracy Grade C7 |
BSST | 8 | 2 | 0.003 or less |
| 10 | 4 | |||
| 12 | 4 | |||
| 15 | 5 | |||
| 10 | ||||
| 20 | ||||
| 20 | 5 | |||
| 10 | 0.005 or less | |||
| 20 | 0.003 or less | |||
| 25 | 5 | |||
| 10 | 0.005 or less | |||
| Standard Nut Accuracy Grade C10 |
BSSZ BSSR |
8 | 2 | 0.005 or less |
| 4 | ||||
| 10 | 2 | |||
| 4 | ||||
| 10 | ||||
| 12 | 4 | |||
| 10 | 0.10 or less | |||
| 14 | 5 | |||
| 15 | 5 | |||
| 10 | ||||
| 20 | ||||
| 20 | 5 | |||
| 10 | 0.15 or less | |||
| 20 | 0.10 or less | |||
| 25 | 5 | |||
| 10 | 0.20 or less | |||
| 25 | 0.12 or less | |||
| 28 | 6 | 0.10 or less | ||
| 32 | 10 | 0.20 or less | ||
| 32 | 0.15 or less | |||
| Compact Nut Accuracy Grade C10 |
BSSC | 8 | 2 | 0.05 or less |
| 10 | 2 | |||
| 12 | 4 | |||
| 15 | 5 | 0.10 or less | ||
| 10 | ||||
| 20 | 5 | |||
| 10 | ||||
| 25 | 5 | |||
| Block Nut Accuracy Grade C10 |
BSBR | 15 | 5 | 0.10 or less |
| 20 | ||||
| 25 | ||||
| 15 | 10 | |||
| 20 | ||||
| 25 |
Table 5. Backlash of Precision Ball Screws
| Type | Representative Type | Screw Shaft Diameter | Lead | Backlash (mm) |
|---|---|---|---|---|
| Standard Nut Accuracy Grade C3 |
BSX | 6 | 1 | 0 (Fixed Preload) |
| 8 | 1 | |||
| 2 | ||||
| 10 | 2 | |||
| 12 | 2 | |||
| 5 | ||||
| 15 | 5 | |||
| 8 | 2 | 0.005 or less | ||
| 12 | 2 | |||
| 4 | ||||
| 5 | ||||
| Standard Nut Accuracy Grade C5 |
BBS (BSL) |
10 | ||
| 15 | 5 | |||
| 10 | ||||
| 20 | ||||
| 40 | 0.010 or less | |||
| 20 | 5 | 0.005 or less | ||
| 10 | ||||
| 20 | ||||
| 40 | ||||
| 25 | 5 | |||
| 10 | ||||
| 20 | ||||
| Standard Nut Accuracy Grade C7 |
BSSE | 8 | 2 | 0.030 or less |
| 10 | 2 | |||
| 4 | ||||
| 12 | 2 | |||
| 5 | ||||
| 10 | ||||
| 15 | 5 | |||
| 10 | ||||
| 20 | ||||
| 20 | 5 | |||
| 10 | ||||
| 20 | ||||
| 25 | 10 | |||
| 20 |
Lead Accuracy Selection Example
Usage Condition
- ・Screw Diameter ÁE5. Lead 20
- ・Stroke 720mm
- ・Stroke 720mm
Selection Details
Select an accuracy grade that satisfies the application requirements.
- (1) Thread Length Evaluation
- Stroke + Nut Length + Extra Margin = 720 + 62 + 60 = 842mm
* Extra margin is for over-run countermeasure, and should be 1.5~2 times the screw lead.
Lead 20 x 1.5 x 2 (both ends) = 60 - (2) Lead Accuracy Evaluation
- From the Table 1. of P1893, find an allowance value of Actual Mean Travel Error (ep).
C3 --- ±0.021mm/800~1000mm
C5 --- ±0.040mm/800~1000mm - (3) Determine Lead Accuracy
- It can be seen that C5 grade (±0.040mm/800~1000mm) satisfies the application requirement of ±0.05/720mm.
Backlash Selection Example
Application Condition
- ・Screw Diameter Φ15, Lead 5
- ・Allowable Backlash ±0.01mm
Usage Condition
From the Table 5., it can be confirmed that a ÁE5 diameter C5 screw with less than 0.005mm backlash satisfies the application requirement of ±0.01mm.
