Motion Without Limits® Load/Life Relationship
Several factors influence the service life of a DualVee linear guide. Through research and development spanning over thirty years, Bishop-Wisecarver has devised a simple method to estimate the load/life relationship for a specific DualVee guide mechanism under defined loading con- ditions. The methodology accounts for the size of the DualVee bearing elements, relative spacing, and the orientation, location, and magnitude of the load. The equation is based upon clean and well lubricated track conditions; so for applications where lubrication is pro- hibitive, a derating factor must be applied.
It is important to note that secondary considerations such as maximum velocity, acceleration rates, duty cycle, stroke length, environmental conditions, the presence of shock and vibration, and extreme temperature ranges can all impact service life to varying degrees. As such, the sizing method is considered only as a guideline for the sizing of DualVee components and assemblies.
Load/Life Equation – Sizing and Selection The load/life estimation requires a basic understanding of the principles of statics, the ability to work with free body diagrams, and the capacity to resolve externally applied forces on a carriage assembly into the radial and axial reaction forces at each guide wheel in the design. The life of a DualVee guide will be limited to the life of the most heavily loaded bearing in the design.
F F
Step 2: Calculate the load factor for the most heavily loaded bearing
LF = FA + FR FA(max) FR(max)
Where LF = Load Factor FA = Resultant axial load on the guide wheel
FA(max) = The maximum axial working load capacity of the guide wheel
FR = Resultant radial load on the guide wheel
FR(max) = The maximum radial working load capacity of the guide wheel
ƒ Bearings should be sized such that LF 1
ƒ The most heavily loaded bearing will have the highest load factor
Step 3: Calculate life by applying the load factor to the load/life equation below:
Due to varying application load and speed parameters and environmental conditions, the appropriate adjust- ment factor must be applied to the life equation.
Adjustment Application Factor (AF) Conditions 1.0-0.7 0.7-0.4
0.4-0.1 Clean, low speed, low shock, low duty
Moderate contaminants, medium duty, medium shock, low to medium vibration, moderate speed
Heavy contamination, high acceleration, high speed, medium to high shock, high vibration, high duty cycle
Step 1: Calculate the resultant radial and axial loads reflected to each bearing element in the linear guide design
All standard considerations involved in statics calcula- tions must be accounted for, including inertial forces, gravitational forces, external forces such as tool pressure, bearing element spacing, and magnitude and direction of the payload. Any external forces that generate a reaction through the wheel/track interface need to be considered. If assistance is required in resolving specific loads into the resultant reaction forces at the guide wheel interface, contact our Applications Engineering staff for support. It is recommended that the Application Data Sheet on page 29 or online form be submitted beforehand, with as much application information detailed as possible.
ß DualVee Size
0 1 2 3 4
4XL Life = (
LC (LF)3
) AF
Where LF = Load Factor LC = Life Constant AF = Adjustment Factor
23 © Bishop-Wisecarver Corporation 2011. All rights reserved.
www.bwc.com 888.580.8272
ß Inches of Travel Life
1.65 x 106 2.19 x 106 3.47 x 106 5.19 x 106 6.84 x 106 8.58 x 106
ß Life Constant LC
ß Kilometers of Travel Life
41 55 87
130 151 215
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