Compute using pitch circle diameter – Rockwell Automation Motion Analyzer Software User Manual
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Rockwell Automation Publication MOTION-UM004B-EN-P - October 2012
Chapter 2
Sizing Your System
2.4.2. Compute Using Pitch Circle Diameter
Use this mode to compute the desired data (Ratio and Inertia values) by using the
pitch circle diameter. This option is not available for a coupling transmission.
Figure 143 - Compute Using Pitch Circle Diameter Dialog Box
Enter the following parameters for pitch circle diameter, if relevant.
Table 114 - Compute Using Pitch Circle Diameter Properties
Parameters
Description
)
Belt/Chain
Transmission component ratio. If a straight-through coupling is being modeled, set Ratio = 1.
Motor Side Pulley/
(1)
Sprocket/Gear
These values are the Pitch Circle Diameter (PCD) and Inertia for the transmission component on
the motor side.
Load Side Pulley/
Sprocket/Gear
These values are the Pitch Circle Diameter (PCD) and Inertia for the transmission component on
the load side.
Efficiency and Losses
(label 2 in
)
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
on
to calculate the inertia value for your application, if the value is not readily available.