Festo 8060571, Repair Instructions

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22 / 52 Festo 7ELCC_TB_KFb_en
4 Repair preparation
4.1 Determining the causes for the repair
If it is necessary to change the toothed belt, always investigate the cause of the failure in order to prevent premature and
repeated failure. A cantilever axis that has been used as intended and designed correctly will not normally exhibit any
premature signs of failure.
This investigation is not necessary in the case of non-premature failure (fatigue time). However, the condition of the
toothed belt pulley module (wear of the tooth surface/tooth geometry, radial clearance between bearing inner raceway
and the bearing seat: interference fit when new) and also the condition of the deep‑groove ball bearings (e.g. perceptible
bearing clearance, disrupted, non-smooth rolling behaviour and increased running noise, etc.) should always be eval-
uated too. In case of uncertainty, we recommend replacing all the components mentioned to rule out reciprocal effects
during later operation.
Possible visible signs of wear of the toothed belt:
– Cracks on the back of the toothed belt are signs of wear. For example, these can be caused by operation outside the
permitted temperature range, impermissible chemical effects or possibly reaching the end of its fatigue life.
– Toothed belt made of neoprene with nylon coating (CR)
– Wear of the nylon fabric (fabric cover) on the tooth side of the belt. This is indicated by lint and pilling, for exam-
ple, and constitutes primary wear (abrasion of the fabric).
– Visible individual glass fibre cords in the tooth gullet are secondary signs of wear due to primary wear of the
nylon fabric. In this case, the toothed belt pulley module must be examined very carefully for wear, as visible
glass fibre cords may have caused severe abrasive damage to the sides of the tooth tip of the toothed belt pulley.
On replacing the toothed belt due to long operation, it is useful to replace the toothed belt pulley module
including deep-groove ball bearings at the same time (
 Chapter 5 on page 24 ).
– Toothed belt made of polyurethane with uncoated steel cord (PU1)
– The tooth geometry wears very uniformly, so that despite high wear the contour is maintained for a relatively long
time. In addition, the tension members made of steel cord start to protrude out of the PU material, so that iron
oxide forms and colours the abraded toothed belt material red. At this stage, in general there is not yet any visible
damage to the toothed belt pulley module. This status is a good indicator for toothed belt replacement.
– Toothed belt made of polyurethane with steel cord and fabric coating (PU2)
– On replacing the toothed belt due to long operation, it is useful to replace the toothed belt pulley module includ-
ing deep-groove ball bearings at the same time (  Chapter 5 on page 24 ).
In the event of premature failure of the product, the operating conditions should be examined more closely.
The following possibilities should be considered, among other things:
– Overloading
Incorrect set values of the braking ramp in STOP states (e.g. EMERGENCY STOP, quick stop) result in overloading of
the product and can irreparably damage it or reduce its life drastically.
The elasticity of the toothed belt delays the acceleration and braking performance of the product and results in great-
er acceleration and deceleration than set at the controller (spring effect).
Block‑shaped acceleration and deceleration profiles (no jerk limitation) cause high peaks in the drive force that can
lead to overloading of the drive. Positions outside of the permissible range can also occur. An acceleration and de-
celeration specification with jerk limitation reduces oscillations in the entire system and has a positive effect on the
stresses to which the mechanical system is subjected.
• Check which closed-loop controller settings can be adjusted (e.g. jerk limitation, smoothing of the acceleration
profile).
• Check the settings of all braking ramps in the controller or the higher-level control system (deceleration values
and jerk).
• Make sure that the deceleration values (braking deceleration, deceleration times) of the speed, the load to be
moved and the mounting position (horizontal / vertical) and the specified maximum drive torque or the feed force
correspond to the allowable values of the product used.
• Use the Festo “PositioningDrives” design software to design the product (

www.festo.com ).