About SFT
About SFT and DFT
Among other product lines GEI Systems has developed for the gear industry the Single Flank Tester is definitely the main product and it has become the most important tool in getting a quality gearset.
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Instrumentation in form of high accuracy angular optical encoder, sensors for linear motion control and feedback information from prime movers and motion controllers is shipped with every system we have built.
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Modeling of gear cutting process and methods based on different equipment and simulation of that with a very accurate visual depiction using so-called TCA (Tooth Contact Analysis) package developed by GEI Systems is another signature product of GEI Systems in the gear technology area.
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Philosophy used in gear testing for DFT and SFT methods, are different but both methods are very common in any production where gears to be tested.
The most common methods of gear testing/ evaluation process on a component bases outside of assembled product are:
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- Single Flank Test (SFT); for gear sets with any shaft angle
- Double Flank Test (DFT); for gears with almost paralleled shafts.
Double Flank Method (DFT) is based on a simple principal to judge about the “defects” presented in gear surface by measuring the deviations in center distance position when both gears are in “metal to metal” contact on both flanks for both members all the time. No backlash (zero backlash) during the test.
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Single Flank Method (SFT) is based on the idea to run both members: gear and pinion under controlled mounting conditions with only one pair of flanks (one for gear and one for pinion) are in contact by maintaining a positive backlash between pair. The quality of the gearset is judged by the Transmission Error (TE) between both shafts at different mounting conditions.
To achieve that such a system must have two spindles with arbors to hold parts to be tested and a base on which those spindles can be mounted and moved relatively to each other into any desired position using E, P, G and Alpha settings:
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- E represents changes in (shaft offset or) Hypoid offset,
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- P determines pinion cone position change,
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- G determines gear cone position, and
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- Alpha is the shaft angle change.
Practically, any type of gears can be considered as a 6 (six) DOF system.
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Four DOFs, represent mounting conditions commonly known as: E, P, G and Alpha parameters.
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The other two DOFs are rotational RPM of the input (pinion) shaft and the Load applied on the output shaft (gear).
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Since a Single Flank Test (SFT) is based on the idea to run both members under controlled mounting conditions, it is performed outside of the assembled unit when each member is mounted on a very precision and rigid shafts.
Two surfaces in contact will develop a reaction force between both members- sometimes known as a force of separation since it tends to separate one member from another. Those forces will deflect some members of the system involved in a full Free Body Diagram (FBD). Due to this deflection, gear and pinion will move relatively to each other. The result of that is a new “mounting” position of the pinion relatively to the gear, which can be always determined by a set of four parameters: E, P, G, Alpha. At nominal “home” unloaded (unstressed) position those four parameters would have zero values.
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So, the effect of shafts, bearings and supporting structure (housing) deflection can be measured and represented by certain changes in 4 DOF vector with component parameters: E, P, G, Alpha. Working surfaces will just find another relative position in space. What are those numbers and how to get them for different load?
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Gear Deflection System (GDS) is designed to apply those loads and measure the deviations in E, P, G and A for each load. When the process is completed and functions for E, P, G and A are obtained for different loads, those numbers will be used in both TCA and SFT.