| NOOK PRECISION PROFILE RAIL LINEAR GUIDE SYSTEMS GLOSSARY
AND TECHNICAL DATA |
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| ACCURACY STANDARDS
& manufacturing
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CALCULATIONS & desigN recommendations |
| Accuracy Standards
and Recommendations
Parallelism
Rail Length and Straightness
Preload and Rigidity
|
LIfe Calculation
Definition of Rated Load
Static Safety Factor
Determination of Rated Fatigue Life
Calculation of Runner Block Load Calculation
Example
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ACCURACY
STANDARDS & RECOMMENDATIONS |
NOOK Precision Profile Rail
Systems are available in six standard classes. The selected accuracy
grade should match the positioning accuracy and parallelism requirements
of the equipment. The grade of the Profile Rail System should be
matched to the ball screw if used.
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| * Stocked Accuracy |
** see Fig 1 below |
 =
Available |
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LINEAR GUIDE ACCURACY
Please select the most suitable grade of NOOK Precision Profile
Rail System for your application. For accuracy requirements beyond
the tolerances indicated or for any special requirements, please
contact NOOK application engineers.
Running Parallelism
Running Parallelism is defined as the error in the parallelism
between the datum planes of the rail and the runner block as the
runner block is moved along its entire travel length.
Differences in Height “H”
This defines the difference between the maximum and minimum heights
“H” of the runner blocks that are mounted on the same rail. See
figure 1.
Difference in Widths “N”
This defines the difference between the maximum and minimum widths
of “N” between each runner block mounted on the same rail. See figure
1.
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GUIDE RAIL ACCURACY GRADE |
C001
Ultra
Precision |
C01
Super
Precision |
C1
Precision |
C3
High |
C5
Standard |
|
| Rail
Length |
| Min
(mm) |
Max
(mm) |
| - |
315 |
1.5 |
2 |
2.5 |
8 |
16 |
52 |
| 315 |
400 |
2 |
2.5 |
3.5 |
10 |
20 |
57 |
| 400 |
500 |
2 |
3 |
4.5 |
11 |
24 |
63 |
| 500 |
630 |
2 |
3.5 |
6 |
14 |
27 |
70 |
| 630 |
800 |
2.5 |
4 |
8 |
16 |
32 |
80 |
| 800 |
100 |
3 |
4.5 |
9 |
19 |
38 |
90 |
| 1000 |
1250 |
3 |
6 |
11 |
22 |
43 |
105 |
| 1250 |
1600 |
4 |
7 |
14 |
25 |
50 |
125 |
| 1600 |
2000 |
4.5 |
8 |
16 |
29 |
57 |
150 |
| 2000 |
2500 |
6 |
9 |
16 |
30 |
60 |
170 |
| 2500 |
3150 |
6 |
10 |
18 |
30 |
60 |
210 |
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RAIL
LENGTH
The maximum lengths of rail for NOOK Precision Profile Rails are
shown in the table below. Longer lengths can be achieved by butt
joining rails.
RAIL STRAIGHTNESS
To obtain high accuracy guidance, the rail itself must be straight.
It is very difficult to mount a distorted rail on a straight mounting
surface. NOOK rail manufacturing processes ensure straightness for
ease of assembly and long life. Distortion free end cuts are achieved
through an automated, wet, abrasive cut-off saw system. |
| Profile
Rail Model No. |
Profile
Rail Max Length |
| NH-15 |
1500* |
| NU-15 |
| NN-15 |
| NH-20
thru NH-65 |
3000* |
| NH-20
thru NH-55 |
| NH-20
thru NH-50 |
|
PRELOAD
AND RIGIDITY
For correct operation under complex loading conditions, the selection
of a suitable preload for linear motion bearings is essential. For
extended life and accuracy under conditions of vibration and shock,
the best results are usually achieved by using NOOK Precision Profile
Rails with heavy preload.
In general, if preload is applied to the NOOK Precision Profile
Rails, rigidity of the Profile Rail will be doubled compared to
that of a non-preloaded Profile Rail.
The preloaded condition is effective for operating loads of up
to approximately 3 times the value of preload. Therefore, as a guide,
one half to one third of the operating load should be considered
for preload and specified according to tables below.
|
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| Selection
of Preload |
| Preload
|
Conditions
of use |
Application |
T3
Heavy
T2 Medium |
Heavy
cutting or forming work with heavy impact and vibration.
Overhung load or alternate load applied. |
•
Machining center
• Milling machines
• Vertical
axis of machine tools |
T2
Medium
T1 Light |
Medium
cutting or forming
Light work with medium impact and vibration.
Light overhung load or alternate load applied. |
•
Electrical discharge machines
• Surface grinding machines
• Robots.
• Jig grinding machines
•
Laser processing machines
• Printed circuit board
drilling machines.
• High speed punching machines. |
T1
Light
TO Very Light |
Precise
movement with very light vibration.
No overhung load or no alternate load applied. |
•
Precision positioning tables
• Tables of optical measuring
equipment
• Automatic Tool Changer for machining centers
• Welding machines
• Material feeding devices |
TO
Very Light
T Clearance |
Extreme
changes in temperature.
High precision not required. |
•
Tool changers Material feeding devices
• Plasma cutting
machines |
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life
All of the following factors should be taken into consideration
when selecting a NOOK Precision Profile Rail System:
The rolling elements and raceways of a NOOK
Precision Profile Rail System that support a load are always subject
to cyclic stress. Eventually, part of the raceway may spall due
to metal fatigue. The life of a linear motion system is defined
as the total distance of the travel reached by the time that first
fatigue spalling occurs, either from a rolling element or raceway.
1. Definition
of Rated Load
- Dynamic load ratings C
C (kN) is the operating load which specifies 50km of travel. (1
kgf=9.81 Newtons=0.2248 lbf)
- Static load ratings Co
Co (kN) is the load that causes a permanent deformation equal
to 1/10000 of the ball diameter at the contact point between the
ball groove and the steel ball.
- Static moment ratings M
M (kN-m) is the moment which causes a permanent deformation equal
to 1/10000 of the ball diameter at the contact point between the
ball groove and the steel ball when a moment load is applied.
For C, Co, M of each model refer to dimensional table.
NOOK Precision Profile Rails have the same
dynamic load capacity in four directions: radial, reverse-radial
and bi-lateral. |
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2.
Static Safety Factor
Generally, the maximum permitted static load
on the runner block is equivalent to static load ratings Co. However,
in repeated linear motion applications, unexpected load is caused
by the inertia when the system starts or stops. Therefore, the safety
factor fs should be calculated in order to determine
the allowable load. |
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Co = static
load ratings
Po = equivalent load (static load, impact load)
fs = static safety factor
The value of fs for general use is indicated in the table below. |
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3.
Determination of Rated Fatigue Life
Dynamic load ratings C (kN), number of strokes per minute and rated
fatigue life L (km) are related as follows: |
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L = expected
life
C = basic load ratings
P = equivalent load |
Where the stroke ls
(m) and the number of cycles per minute n1 (cpm) are constant, the
rated fatigue life Lh (hr) is calculated by the following formula. |
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Lh = expected Life (hr)
ls = stroke length (m)
n1 = number of strokes per minute
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4.
Calculation of Runner Block Load
Driving factor and contact factor
The load acting upon the runner block is the sum of all of the loads
applied such as the weight of the table, the cutting force and the
inertia force caused by the change of speed or by heavy impact or
vibration.
Loads other than the weight of the table are
often difficult to calculate. If in doubt, the applied load should
be multiplied by a driving factor fd (table below)
to give the effective external load. |
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| In most installations each rail
is fitted with at least two runner blocks. The distribution of load
across each runner block is very much influenced by the mounting accuracy
or machining accuracy of the table. Therefore, the contact factor
in the table below should be taken into account. Multiply the load
by this factor. |
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Effect of
preload on internal load of runner block
Internal load PA is determined by external force F and
preload of runner block PPL. |
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Resultant
force of vertical load and horizontal load
Resultant force of vertical load Pv and horizontal load
PH is determined as follows: |
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Resultant
force of radial load and moment load
Resultant force of radial load F and moment load M is determined
as follows.
CO = rated static load
MO = rated static torque on M direction
|
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Mean load
vs. load variation
In applications where the load onto the runner block varies, mean
load should be considered instead of discrete load variations P1,
P2...Pn.
1) For cases where the load and travel vary gradually: |
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Pe = mean load (kN)
Pn = load step (kN)
L = total travel (m)
Ln = distance travelled by Pn (m)
|
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| 2) For cases where
the load vary abruptly: |
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Pmin: min. load (kN)
Pmax: max. load (kN)
|
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3) Sinusoidal load
change:
Pe ~ O.65 Pmax (Fig.A)
Pe ~ O.75 Pmax (Fig.B)
|
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Frictional
resistance
For correct load calculation, frictional resistance of the runner
block must be included. Frictional resistance is calculated using
the following formula.
|
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F = frictional resistance force (kN)
W = slide load (kN)
µ = coefficient of friction
f = seal resistance force (kN)
The coefficient of friction for NOOK Precision Profile Rails is
typically O.OO3~O.OO5 with no preload. Seal resistance force per
runner block is typically .00196~.002942 kN.
Example: For a slide load (W) of 15.69 kN on 4
runner blocks of NH- TR model, the frictional resistance (F) is
calculated:
F = µW + f = (O.004 x 15.69) + (O.3 x 4) = .0745 kN
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Load on the
runner block
The loads acting on a linear motion system vary according to the location
of the center of gravity, the thrust, position, moment, loading speed
changes by acceleration and deceleration, cutting forces and other
external forces. It is important that all of these parameters are
considered at the design stage. |
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5.
Calculation Example
Determination of RUNNER BLOCK LIFE.
A sample calculation of runner block life is shown below.
Model NH35TR
Stroke, s = 1m
Load, W = 9.8 kN
Driving factor, fd = 1.2
Contact factor, fc = O.86
2 rails, 4 runner blocks
No. of cycles, n1 = 5 cpm |
 |
Life of the No.2 runner
block which experiences the highest load is determined from C=37.55
kN obtained from the
dimension table. |
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Selection
of a suitable Profile Rail Assembly
as a function of required life.
A sample selection is shown below using the following criteria:
Stroke ls = 1m
No. of strokes per minute n1 = 5 cpm (1Om/min)
Expected life Lh = 25000 hr
Load W = 19.61 kN
Driving factor fd = 1.5
Contact factor fc = O.86
|
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NH45TR
(C=60.20 kN) which has the required dynamic load rating is selected
from the dimension table (page 37).
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Determination
of runner block life (single axis)
A sample selection is shown below using the following criteria:
Model NH35TR
Rated dynamic load capacity C = 37.55 kN
Rated static load capacity CO = 62.55 kN
Load W = 1.96 kN
External force F = .196 kN
Driving factor fd = 1.4
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DESIGN
RECOMMENDATIONS/GUIDELINES |
1. Mounting
Shoulder Height and Corner Fillet
In order to provide a register to align the rail or the runner blocks,
mounting surfaces should be machined according to the diagram below
with shoulder height and corner radii dimensions as shown in the
accompanying table.
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2. Indication
of Reference Edge
NOOK Precision Profile Rails have a reference edge on both the rail
and the runner block. See below. |
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3. Installation
of Rail and Runner Blocks
Use any one of the three methods shown below.
The locking set screws should be positioned at the same location
as the mounting bolts.
Better alignment is obtained by machining reference edges for both
runner block and rail. For optimum performance, the accuracy of
the mounting surface should equal that of the rail.
Note: Care should be taken when removing the runner block
from the rail to avoid balls deflecting the ball retainers and thus
falling out. |
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4. System
Design Configurations for Nook Precision Profile Rails
Shown below are various various installations for profile rail systems.
One through four are the most common. Five through eight are for limited
height applications. Number nine is the least accurate. |
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Proper lubrication and contamination protection are an essential
requirement for NOOK Precision Profile Rails.
Seal
A standard feature of NOOK runner blocks is a special composite
rubber or felt seal that effectively retains grease (lithium soap
base) within the runner block.
Mounting Hole Caps
For sealing quality and protection use the cap plugs supplied by
NOOK to cover the mounting holes in the rail flush with the top
surface.
Grease Fittings
Lubrication is recommended every six months or after every 100km
(about 330,000 ft.) of travel. If lubrication every six months or
100km is not practical, forced oil lubrication is necessary. Refer
to the catalog pages for the runner block types to determine the
style of grease fitting supplied. |
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Orientation
of Reference Surface and Grease Fitting |
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Bellows
Covers for Profile Rail Assemblies |
| When additional protection
is required the use of NOOK bellows is recommended. The chart below
indicates the bellows dimensions. PVC coated nylon material is used
exclusively. Neoprene-cloth and chemically resistant materials are
also available upon request. |
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