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Festo 7DGE_ZR_RFb_en
4
Repair steps
This chapter describes how to dismantle, repair and assemble the toothed belt axis DGE-…-ZR-RF. This is done by first
dismantling the device into individual modules (subsequent sections deal with the repair of these modules). Depending
on the cause of the defect to be eliminated it may be necessary to exchange several components. The cause of a defect
must therefore always be determined before starting a repair.
Note
The repair should preferably be carried out on a stable and flat work surface with storage for small parts. It is also
possible to repair the toothed belt axis in installed condition, if required.
4.1
Renewing the toothed belt
Note
The toothed belt can be renewed with the toothed belt axis in installed condition if it is not torn or if the location of the
tear is visible as in that case it is not necessary to disassemble the drive covers. The drive covers must be removed if
the tear is located in the drive covers or the cylinder barrel (see section
4.2.1 “Removing the drive covers”
Should it be necessary to change the toothed belt, the cause of the failure must be investigated to prevent premature
and repeated failure. A toothed belt axis that has been used as intended and sized correctly will not normally exhibit any
premature signs of failure.
This is not necessary in the case of non-premature failure (fatigue time). However, the condition of the toothed belt pulley
module (wear to the surface/shape of the teeth, radial play of the bearing inner raceway with respect to the bearing seat:
tight fit in new condition) and also the condition of the deep-groove ball bearings (e.g. perceptible bearing clearance,
impaired roll-off behaviour and increased operating noise, etc.) should always be checked. In case of uncertainty, it is
recommended to replace all the components mentioned so as to rule out reciprocal effects during later operation.
Possible visible signs of wear to the toothed belt:
• Tears on the back of the toothed belt are signs of wear, for example caused by operation outside the permitted tem-
perature range, impermissible chemical influences or possibly fatigue.
• Wear to the nylon fabric (fabric coating) on the tooth side of the belt. This is indicated by lint formation and bobbling,
for example, and constitutes primary wear (abrasion of the fabric).
• Visible individual glass fibre tensile strands in the tooth base are secondary signs of wear due to primary wear to the
nylon fabric. If this happens, the toothed belt pulley module must be carefully examined for wear since visible glass
fibre tensile strands may have had a severe abrasive effect on the tooth tip sides of the toothed belt pulleys.
A description of how to replace the toothed belt pulley module together with the corresponding deep-groove ball bearings
can be found in section
4.2.2 “Dismantling the drive covers”
.
If the toothed belt suffers premature failure, the operating conditions should be looked at more closely.
The following possibilities should be considered among others:
• Overloading
The elasticity of the toothed belt retards the acceleration and braking behaviour of the toothed belt axis and results
in greater acceleration and deceleration than set in 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 adapted (e.g. jerk limitation, smoothing of the acceleration
profile).
