TERMS OF LINEAR GUIDE

1-1 Major Factors

a. Load and Life (L)

Choosing a linear guide has to consider the following variables to conclude a reliable static safety factor: average applied load on every slide, basic static nominal load(C0) or basic permissible static moment(Mx、My、Mz). In case of calculating life in a long-term consumed environment, it requires basic dynamic nominal load(C) for an approximate result.
 

b. Basic static load rating (C0)

When a linear motion system in the static state or in motion is subject to an extreme load or impact, a permanent deformation will occur between raceway and rolling elements. If the deformation is excessive, the linear motion system can not travel smoothly. Now, we define the basic static nominal load(C0) is a static load of constant magnitude acting in one direction under which the sum of the permanent deformations of rolling elements and raceway equals 0.0001 times the diameter of the rolling elements.
 

c. Basic permissible static moment

When a linear guide gets a force that makes the balls distorted to 1/10,000 of theirs diameter, we call the force as basic permissible static moment.
 

d. Static safety factor (fs)

The static safety factor indicates the ratio of Basic static nominal load(C0) to the load acting on the linear motion system.
 

e. Nominal life (L)

The nominal life L is the total distance of travel reached without flaking by 90% of a group of identical linear motion system that are operated independently under the same condition.
 

f. Basic dynamic load rating(C)

When each of a group of identical linear motion system is applied independently under the same condition, basic dynamic load rating C is the load of constant magnitude acting in one direction that results in a nominal life of 50 km for a system using balls.

1-2 Subsidiary Factors:

a. Contact factor (fc)

In linear motion system, it is hard to obtain uniform load distribution in close contact installation due to moments, errors on the mounting surfaces and other factors. When two or more blocks in a rail are used in close contact, multiply basic load ratings C and C0 by the contact factors shown below.

Number of blocks in close contact	Contact factor
2	0.81
3	0.72
4	0.66
5	0.61
Normal operation	1

b. Hardness factor (fh)

When working environment temperature exceeds 100 degrees Celsius, ft becomes a key factor.

c. Temperature factor (ft)

When working environment temperature exceeds 100°C, ft becomes a key factor.

Remark:
When working environment temperature exceeds 80 degrees Celsius, the material of seals and cages have to be able to endure the high temperature.

1. Confirming conditions

It takes engineering calculation when adapting a linear guide system, and the must knows are:
A. Composition: (distance between 2 blocks / rails number of blocks, number of Rails.)
B. Mounting: (Horizontal, erect, on a slant, wall installation, or upside down Mounting.)
C. Applied load
D. Frequency of use

A. Composition:

1. Distance between 2 blocks / rails: L0&L1 as shown.
L0: Distance of two blocks loaded on the same rail (mm)
L1: Distance between one rail to another (mm)
The distance of L0 and L1 matters the rigidity and life of the linear guide system itself.
2. Number of blocks: in general cases, the more blocks used on a rail, the better the rigidity and the higher load capacity. However, layout plan and stroke have to be reconsidered.3. Number of rails: when increasing the quantity of rail, the moment resistance of X axis enhances and so do rigidity and load.

b. Installation:

1.Horizontal Installation

c. Applied load

Load contains 3 elements: force, direction of load and object that is loaded.

d. Frequency of use:

Frequency of use has to be added into considerations when proving whether the engineering calculation fit the actual application.

2-3 Selecting An Optimal Model

BGX or BGC

Choosing workable size should be based on the type of the machine center.
Introductions of BGC and BGX of linear guide are attached in the following
content.
b.15、20、25、30、35
Size should be the first point as selecting a linear guide for a new working system because load and exact life are difficult to calculate at the beginning. As the result, when there is a difference between calculated life and actual load, move to a size with larger dynamic load rating.

2-4 Calculating Applied Load:

Equation of vertical forces onto the block.

2-5 Calculation Of Equivalent Load

The contact arc between a rail and a block decides the ratio of those forces from horizontal and vertical directions which happening to the block. Equivalent load means the maximum force that the groove could take. It needs to have the vertical and horizontal forces to calculate the equivalent load, and distribute it by different directions. For instance, the load of 45° design is the absolute value of horizontal force plus the absolute value of vertical force.
Rn: Divided vertically load
Sn: Divided horizontally load
Equivalent load Re comes from:
Re = │Rn│+│Sn│

2-6 Confirming Static Safety Factor

Contact factor (fc)

In linear motion system, it is hard to obtain uniform load distribution in close contact installation due to moments, errors on the mounting surfaces and other factors. When two or more blocks in a rail are used in close contact, multiply basic load ratings C and C0 by the contact factors shown below.

Number of blocks in close contact	Contact factor
2	0.81
3	0.72
4	0.66
5	0.61
Normal operation	1

2-7 Reference Of Static Safety Factor

Reference value of static safety factor fs shown below:

Operating condition	Load condition	Minimum fs
Normally stationary	Small impact and deflection	1.0 ~ 1.3
	Impact or twisting load are applied	2.0 ~ 3.0
Normally moving	Small impact or twisting load are applied	1.0 ~ 1.5
	Impact or twisting load are applied	2.5 ~ 5.0

2-8 Calculating Mean Load

Calculation of changing mean load can be diversified into the following models:
STEP LOAD:

線性負載型式

Pm≒(Pmin+2xPmax)/3
Pmim: Minimum load (kgf)
Pmax: Maximum load (kgf)

2-9 Calculating Nominal Life

L: Nominal Life (km)
C: Basic dynamic rating load (kgf)
P: Calculated average load (kgf)
fc: Contact factor
fh: Hardness factor
ft: Temperature factor
fw: Load factor

2-10 Calculating Life Time

2-11. Comparing With Desired Life

If comparing the calculated life and desired life and come up with an unacceptable difference, look back to the flow chart:
    1. Confirming conditions
    2. Selecting an optimal mod

    1. Reconfirming the conditions of use:
a. Composition?
i. Distance of each two rails and blocks
ii. Number of blocks
iii. Number of rails

    b. Mounting: how the rail is mounted onto the system?
c. Load capacity?
d. Frequency of use?
 
2. Selecting another model:
    When conditions of use cannot be changed, select another feasible model is suggested. In addition, choosing another block of the same size with heavier load capacity is firstly recommended. Replacing the original choice with other sizes, such as size 15 to size 20, would raise the cost and add changes to the design. Contact us when technical assistance is required.

2-12 Model Number Coding

  Unit: mm

ITEM GRADE	Normal(N)	High(H)	Precision(P)	Super-Precision(SP)	Ultra-Precision(UP)
Tolerance of height ( H )	±0.1	±0.04	0 -0.04	0 -0.02	0 -0.01
Tolerance of width ( W )	±0.1	±0.04	0 -0.04	0 -0.02	0 -0.01
Difference of heights (△H )	0.03	0.02	0.01	0.005	0.003
Difference of widths (△W )	0.03	0.02	0.01	0.005	0.003
Running parallelism of BR Block surface C with respect to surfaceA	△C Refer to the below Fig. BG rail length and running parallelism
Running parallelism of BR Block surface D with respect to surface B	△D Refer to the below Fig. BG rail length and running parallelism

b. Choosing preload

   Replacing larger rolling elements helps strengthening the entire rigidity of the
   carriage while there exists clearance within ball circulation.

Preload	Slight clearance/ no preload (ZF/ Z0)	Light preload (Z1)	medium/ heavy preload (Z2/ Z3)
Conditions of use	1. Light corrosion 2. 2 parallel axes 3. Low accuracy 4. Low friction 5. Light load	1. Cantilever 2. Mono axis. 3. Light load 4. High accuracy	1. Heavy corrosion 2. Severe vibration 3. Heavy cutting
Application	1.Welding machine 2. Cutting machine 3. Feeder 4. ATC 5. X & Y axis 6.Packaging machine	1. NC Lathe 2. EDN 3. Precision XY table 4. Robotic manipulator 5. Z axis 6. PCB drilling machine	1. Machine center 2. NC Lathe 3. Milling machine 4. Grinding wheel feed shaft

Increasing preload would diminish the vibration and reduce the corrosion caused by running back and forth. However, it would also add the workload within those rolling elements. The greater the preload, the greater the inner workload. As a result, choosing preload has to consider both how vibration and preload would affect life and conclude an optimal choice.

Preload grade

 

C:Basic dynamic load rating
GRADE ITEM	Symbol	Preload force
Clearance	ZF	0
No Preload	Z0	0
Light Preload	Z1	0.02C
Middle Preload	Z2	0.05C
Heavy Preload	Z3	0.07C

Radial clearances

Unit: μm
Symbol Type	ZF	Z0	Z1	Z2	Z3
BG 15	5~12	-4~4	-12~-5	-20~-13	-28~-21
BG 20	6~14	-5~5	-14~-6	-23~-15	-32~-24
BG 25	7~16	-6~6	-16~-7	-26~-17	-36~-27
BG 30	8~18	-7~7	-18~-8	-29~-19	-40~-30
BG 35	9~20	-8~8	-20~-9	-32~-21	-44~-33
BG 45	10~22	-9~9	-22~-10	-35~-23	-48~-36

Interchangeability

Accuracy	Non - interchangeable					Interchangeabl
	UP	SP	P	H	N	H	N
Preload					ZF		ZF
			Z0	Z0	Z0	Z0	Z0
	Z1	Z1	Z1	Z1	Z1	Z1	Z1
	Z2	Z2	Z2	Z2	Z2
	Z3	Z3	Z3

ITEM	Unit: μm
	e1					e2
	Z3	Z2	Z1	Z0	ZF	Z3	Z2	Z1	Z0	ZF
BG 15			18	25	35			85	130	190
BG 20		18	20	25	35		50	85	130	190
BG 25	15	20	22	30	42	60	70	85	130	195
BG 30	20	27	30	40	55	80	90	110	170	250
BG 35	22	30	35	50	68	100	120	150	210	290
BG 45	25	35	40	60	85	100	140	170	250	350

Cap:

Most chippings are blocked by end seals, but some would stay in the screw
holes. Caps are accessory that can prevent the entry of chippings.
Rail with tapped holes:
Fixing a rail with tapped hole is different from fixing a standard one. A major
strength of it is the shape of the tapped hole (shown as fig.); dust and chippings
would not enter.

d. Accessories of block

Coding of seal end seal side seal inner seal (top seal) double end seal (double front seal) scraper (metal front shield) Not specified ˇ ˇ       UU ˇ         ZZ ˇ ˇ     ˇ DD   ˇ   ˇ   KK   ˇ   ˇ ˇ SS ˇ ˇ ˇ     SD   ˇ ˇ ˇ