Rockwell Automation Motion Analyzer Software - Manual (Page 195)

Rockwell Automation Publication MOTION-UM004B-EN-P - October 2012 195
Sizing Your System Chapter 2
2.4.3. Compute Using Number of Teeth
Use this mode to compute the desired data (ratio and inertia values) by using the
number of teeth. This option is not available for a coupling transmission.
Figure 144 - Compute Using Number of Teeth Dialog Box
Enter the following parameters for number of teeth, if relevant.
Table 115 - Compute Using Number of Teeth Properties
Parameters Description
Inertia and Ratio
(label 1 in
Figure 144 )
Belt/Chain
This is the mass and tooth pitch for the belt/chain. This value is required for belt drive and chain
and sprocket transmission components only.
Motor Side Pulley/
(1)
Sprocket/Gear
These values are the Number of Teeth and Inertia for the transmission component on the motor
side.
Load Side Pulley/
(1)
Sprocket/Gear
These values are the Number of Teeth and Inertia for the transmission component on the load
side.
Efficiency and Losses
(label 2 in
Figure 144 )
Efficiency
Efficiency is widely misused. It refers to the ratio of output power to input power for a single
operating condition, but a servo system typically operates over a wide range of operating
conditions. A gearbox supplier normally specifies the efficiency at an optimum point such as
full load and full speed.
For example, a gearbox that has an output rating of 100 N•m (885 lb•in)and an efficiency of
98%. This means that the losses at full load are 2 N•m (18 lb•in). But because most of the losses
in a gearbox are due to shaft seal friction and churning of the lubricant, this would not reduce
significantly at a lower load torque.
In using this gearbox, a well-matched servo motor only has a continuous rating around one
third of the peak torque, and it is quite likely that the average torque over the motion cycle
would be even lower, for example about 20 N•m (177 lb•in) at the gearbox output. The losses of
2 N•m (18 lb•in) amount to 10% of the load on the motor, which can have a significant effect
on the temperature rise of the motor.
Motion Analyzer software overcomes this problem by dynamically computing the real losses
throughout the motion cycle, and thereby avoids underestimating the effect of losses on the
motor.
Friction Torque
This is the torque caused by friction on the motor side between the rotor and the transmission
component. This value can be obtained from the supplier or Engineering tables.
(1) Use the Inertia Calculator Template on page 105 to calculate the inertia value for your application, if the value is not readily available.