Page 1674 - MiSUMi 2025

[Technical Data]
Selection of Ball Screws 1

1. Ball Screw Selection Guidelines
Basic ball screw selection procedure and required evaluation items are shown below.
Determination of Operating Conditions Moving mass, feed speed, motion pattern, screw shaft rotational speed, stroke,
mounting orientation (horizontal or vertical), life, positioning accuracy

Interim selection of ball screw specifications Temporary selection of ball screw lead accuracy grade (C5~C7),
shaft diameter, lead, and length. P.B-029 , B-030
NG •Axial Load Capacity
Evaluation of various basic safety factors Confirm that the applied axial load is within the ball screw's axial load capacity rating.
P.B-031
•Allowable Rotational Speed
Confirm that the intended shaft rotational speed is within the ball screw's allowable rotational speed
rating. P.B-032
•Life
Confirm that the service life of the ball screw meets the required lifespan. P.B-033
NG
Evaluations based on required performances If higher positioning accuracy and/or improved responsiveness is needed, below parameters need to be evaluated.
•Screw shaft rigidity
•Effects of temperature variation on life P.B-034
2. Ball Screw Lead Accuracy
Ball screw lead accuracy is defined by JIS Standards property parameters (ep、vu、v300、v2Q).
Parameter definitions and allowable values are shown below.
In general, a ball screw lead accuracy grade is selected by evaluating if the Representative Travel Error of a candidate is within the
allowable positioning error.
Q Table 1. Positioning Screw (C Class) Representative Travel
Effective Thread Length ( lu ) Error (±ep) and Variation (u) allowances
Actual Travel ( la ) Line Nominal Travel ( lo ) Line Unit : μm
+ Representative Travel ( lm ) Line Specified Travel ( ls ) Line Thread Effective Length (mm) Accuracy Grade
Travel Error 0’ 0 over or less Representative Variation
C5
Travel Error
23
315
18
20
500
400
27
0 t 315 400 25 20
− V 0 3
500 630 30 23
630 800 35 25
800 1000 40 27
p 1000 1250 46 30
π e
2 V 1250 1600 54 35
2π u V
300mm Q Table 2. Positioning Screws (C Class) Variation per 300mm
(300), Variation per rotation (2π) standard values
Unit : μm
Accuracy Grade C5 C7
Terms Symbols Meaning
Representative ep A value that is Specified Travel subtracted from Parameters V300 V2π V300
Travel Error Representative Travel. Standard 18 8 52
The maximum difference of the actual travel contained Values
between two lines drawn parallel to the Representative
Travel, and is defined by three parameters below.
Variation uu Variation for the effective thread length of screw shaft.
Variation for an arbitrarily taken length of 300mm within
u300 the effective thread length of screw shaft.
Variation for an arbitrary one revolution (2πrad) taken
u2Q
within the effective thread length of screw shaft.
Specified ls Axial travel compensated for temperature rise and
loading conditions, in relation to the Nominal Travel
Travel (Lead).
A value that is Nominal Travel subtracted from
Specified Specified Travel, over the effective thread length.
Travel Target t This value is set to compensate for possible screw
shaft expansion and contraction due to temperature
Value changes and applied loads. The value is to be
determined based on experiments or experiences.
Actual Travel la Actually measured travel distance
A straight line representing the actual travel trend.
Representative lm A straight line obtained by the least-squares method
Travel or other approximation methods from the curve
representing the actual travel.
B-029