Research into the reasons behind backlash errors in harmonic drives

The requirements of reliability, durability, accuracy, and rigidity of gears used in machinetools, industrial robots and automatic control systems have increased dramatically in the last few decades. A whole new area of research has emerged associated with the development of precision machines and machine-tools with mechatronic units, control systems that use high accuracy mechanical transmissions. Harmonic drives with wave generators of internal and external deformation are considered to be most suitable to satisfy these requirements. The main requirements placed upon harmonic drives are those of kinematic accuracy and torsional rigidity. Deformations of the flex spline and wave generator components, and manufacturing errors in the gears are the main reasons that can cause kinematic errors and reduce torsional rigidity. To improve kinematic accuracy, increase torsional rigidity and achieve continuous torsional rigidity (absence of pitch play) it is proposed that flexible deformations of the gear components and backlashes of the engaged teeth should be mini mized at the design stage. Backlash elimination in the gearing under loading should also be taken into account. It will result in a backlash-free wave gearing with minimal kinematic errors and high torsional rigidity. The suggested method has undergone experimental testing. 

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