Temperature Compensation; General Information - Siemens SINUMERIK 840D sl Function Manual

5.2

Temperature compensation

5.2.1

General information

Deformation due to temperature effects
Heat generated by the drive equipment or high ambient temperatures (e.g. caused by
sunlight, drafts) cause the machine base and parts of the machinery to expand. The degree
of expansion depends on the temperature and the thermal conductivity of the machine parts.
Effects
Due to the thermal expansion of the machinery, the actual positions of the axes change
depending on temperature. Since this phenomenon impairs the accuracy of the machined
workpieces, it is possible to compensate such temperature-related changes in actual value
position (so-called temperature compensation).
Sensor equipment
To provide effective temperature compensation, a number of temperature sensors for
acquiring a temperature profile are needed in addition to the actual position data from
existing encoders.
Since temperature-dependent changes occur relatively slowly, the PLC can acquire and
preprocess the temperature profile in a minutes cycle, for example.
Error curves
In order to implement temperature compensation, the actual-value offsets over the
positioning range of the axis must be measured at a given temperature (T) and plotted. This
produces an error curve for this temperature value. Error curves must be produced for
different temperatures.
Error curve characteristic
The error curve characteristic shown in the diagram below is frequently obtained.
If a position reference point P
(corresponds to the "position-independent component" of the temperature compensation)
can be observed as the temperature changes, and because of the change in length an
additional offset in the other position points which increases with the distance to the
reference point (corresponds to the "position-dependent component" of the temperature
compensation).
The error curve for a given temperature T can generally be represented with sufficient
accuracy by a straight line with a temperature dependent gradient and reference position
(see diagram below).
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
is chosen for the axis, an offset in the reference point
0
Compensations (K3)
5.2 Temperature compensation
339