404LXR Series Product Manual
Chapter 4 - Performance
35
Compensating for Thermal Effects
How much you will have to compensate for the above thermal effects depend on the application
requirements for accuracy. If your accuracy requirements are high, you either need to control base
temperature or program a thermal compensation factor into your motion program.
Controlling the
base temperature
is the best method. However, this means controlling the ambient temperature by
removing all heat/cold generators from the area and operating at very low duty cycles.
Compensation
is the other way of achieving accuracy without sacrificing performance. In this case
the system must be exercised through its normal operating cycle. The temperature of the base
should be measured and recorded from the beginning (cold) until the base becomes thermally
stable. This base temperature should be used in a compensation equation. Below is the
fundamental
thermal compensation equation
:
Cd = (Id - ( (Id) * (Te) *
T))
Cd = Corrected displacement (mm)
Id = Incremental displacement (mm)
Te = Thermal Expansion (0.000022 mm/mm/
C)
T = Temperature Differential from 20
C
Example:
•
Base Temperature of 32
C
•
Required move 100mm
Cd = 100mm - (100mm * Te * 12
C) =
99.9736mm
In this move the commanded move should be 26.4 microns less (100mm
– 99.9736mm) than the
desired move. This will compensate for the thermal expansion of the scale.
This is a simple linear correction factor and can be programmed in to most servo controllers using
variables for the position commands.
