Mileage life and time life calculation method for LM Guide

Today, we are going to discuss the "Mileage life and time life calculation method for LM GuideA note on "The

When calculating the life of the LM Guide, please refer to the following formula to calculate the life of the LM Guide. This formula is a compilation of those listed in the "THK Catalog. This formula is based on the case where the pressurization is not taken into account.

A word of caution here,What is life expectancy anyway?　Why do we need to look at it?　For example, THK's definition of life expectancy is as follows.

Reference: THK (from catalog: calculation of rated life)

The life of the LM guide varies even when similarly manufactured products are used under the same operating conditions. For this reason, the rated life defined below is used as a guide to determine the life of LM guides. Rated life is the total distance that the 90% can travel without flaking (scaly separation of the metal surface) when a group of identical LM guides are individually operated under the same conditions.

Misumi defines it this way.

Citation: MISUMI (from Linear Guide Life Calculation)

When a linear guide undergoes linear reciprocating motion under load, repeated stress constantly acts on the rolling elements (steel balls) and transfer surfaces (rails), causing scaly damage called flaking due to material fatigue. The total distance traveled before the first flaking occurs is called the life of the linear guide.

Rated life is the total distance that 90% of a group of identical linear guides can travel without flaking when they are run individually under the same conditions.

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)Flaking (scaly delamination of metal surface) causes malfunction　Therefore, it is necessary for us designers to provide LM guides that can operate stably during the customer's required service life, and to make efforts to extend the service life by distributing the load well so that abnormal loads are not applied to the guides.

The rated life of the LM Guide is90% do not cause flaking　In addition, abnormal load may be applied depending on the assembly and the accuracy of the LM mounting surface, so please make sure that the size of the LM guide is reasonable.　　Now, we will write down the method of calculating the life of the LM guide.

LM Guide life calculation method

Now, I will note how to calculate the life expectancy of the LM Guide, but there is a prerequisite.　That is.

This means that　In addition, in calculating the life of the LM guideThe calculation method also differs depending on the type of LM GuideSo, please do not make a mistake in your choice here to calculate the life span.

• LM guide using a ball
• Oil-free LM Guide
• LM guide using rollers

Formula for calculating the rated life of an LM guide using a ball

Rated life of LM guide with ballThe following items are necessary to determine the life of the LM guide. These coefficients vary depending on the model of the LM guide and other factors, so the life of the guide will depend on the capabilities of the LM guide selected.

L : Rated life (km)
C : Basic動Rated load (N)←Please pay attention to the value in the catalog.
P C ： Calculated load (N)
f H : hardness coefficient (general coefficient of LM guide = 1.0)
f T : Temperature coefficient (use at 100°C or less = 1.0 150°C = 0.9 200°C = 0.7)
f C : contact coefficient (normal use = 1.0 block 2 pieces close use = 0.8)
f W : load coefficient (V≤0.25m/s=1.0 0 0.25＜V≤1m/s=1.2 1＜V≤2m/s=1.5 V>2m/s=2.0)

Please refer to the following formula for life expectancy calculation.

Citation:Symbols "Ca" and "C0a" for load rating in THK's ball screw catalog

Supplement] "C" and "C0" for load rating in the LM Guide

Incidentally, the basic load rating in the LK Guide is called,

• C: Basic dynamic load rating (N)
• C0: Basic static load rating (N)

As with ball screws, "basic dynamic load rating ＜ basic static load rating

 

Rated life calculation formula for oil-free LM guides

Determine the rated life of an oil-free LM guideThe following items are required for

L : Rated life (km)
F 0 : Allowable load (N)
P C ： Calculated load (N)
f W : load coefficient (V≤0.25m/s=1.0 0 0.25＜V≤1m/s=1.2 1＜V≤2m/s=1.5 V>2m/s=2.0)

Please refer to the following formula for life expectancy calculation.

Formula for calculating the rated life of an LM guide using rollers

Find the rated life of an LM guide with rollers.The following items are required for

L : Rated life (km)
C : Basic dynamic load rating (N)
P C : Calculated load (N)
f H : hardness coefficient (general coefficient of LM guide = 1.0)
f T : Temperature coefficient (use at 100°C or less = 1.0 150°C = 0.9 200°C = 0.7)
f C : contact coefficient (normal use = 1.0 block 2 pieces close use = 0.8)
f W : load coefficient (V≤0.25m/s=1.0 0 0.25＜V≤1m/s=1.2 1＜V≤2m/s=1.5 V>2m/s=2.0)

Please refer to the following formula for life expectancy calculation.

How to calculate lifetime time

When each of the above rated life (L) is obtained,Lifetime time for constant stroke length and number of round tripsis obtained by the following formula
The following is a list of the most important factors that must be taken into consideration when selecting the product.

Lh : Life time (h)
Ls ： stroke length (mm)
n 1 : Number of round trip per minute (min-1 )

Download Calculation Excel Sheet

Here you can download an Excel sheet that allows you to perform mileage life and time life calculations for the LM Guide.

This Excel sheet can be used to calculate the above 4 patterns. Please customize it as you like. For details on each factor, please refer to THK's catalog. (They are also listed in the Excel sheet.)

Mileage life and time life calculation method for LM Guide_191211

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That's it.