Chapter 9 Rigidity - Harmonic Drive CSF-3 Series Manual

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Table Of Contents

Table of Contents

Chapter 9

Rigidity and backlash of the drive system greatly affects the performance of the servo system. A detailed

review of these items is required before designing the equipment and selecting a model number.

Rigidity

Fixing the input side (wave generator) and applying torque to the

output side (flexspline) generates torsion almost proportional to

the torque on the output side. Figure O18-1 shows the torsional

angle quantity on the output side when the torque applied on the

output side starts from zero, increases up to +T0 and decreases

down to –T0. This is called the "Torque – torsional angle diagram,"

which normally draws a loop of 0-A-B-A'-B'-A. The slope described

in the "Torque – torsional angle diagram" is represented as the

spring constant for the rigidity of Harmonic Drive (unit: Nm/rad).

As shown in Figure 020-2, this "Torque – torsional angle diagram"

is divided into 3 partitions, and the spring constants in the area are

represented as K1, K2 and K3.

K1 – The spring constant when the torque changes from [zero] to

[T1]

K2 – The spring constant when the torque changes from [T1] to

[T2]

K3 – The spring constant when the torque changes from [T2] to

[T3]

Torsional angle can be calculated by the following formulas.

* φ: torsional angle

◆ Torque T is T1 or less:

◆ Torque T is between T1 and T2:

◆ Torque T is between T2 and T3:

The following table shows average values of T1 to T3, K1 to K3 and θ1 to θ2.

Spring constant

Model

No.

Sign

θ1

θ2