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36 SM-EtherCAT User Guide
www.controltechniques.com Issue Number: 2
7.3.9 Profile units
The implementation provides a means to convert profile units into position controller and
drive units. All scaling values are standard profile objects. The following objects are
supported:
For positions, the scaling control includes a feed constant, a gear ratio and an encoder
revolution. These values are combined by the implementation into a simple scaling
numerator and denominator. It is possible to change these values non-cyclically (i.e.
using SDOs), in which case the scaling numerator and denominator and any position
limit values are recalculated in the background. It is not, however, possible to change
these values cyclically (i.e. by mapping PDOs to them).
For velocities, in addition to the position constants described above. These values are
combined into a simple numerator and denominator to scale velocities to internal
velocity units. This scaling also properly handles remainders (i.e. when used on a
reference or feedback, accumulate the remainder and add it to subsequent velocity
values, and when used with a limit, round up or down). It is possible to change these
values non-cyclically (i.e. using SDOs), in which case the scaling numerator and
denominator is recalculated in the background. It is also necessary to re-scale velocity
limit values with the new factor. It is not possible to change these values cyclically (i.e.
by mapping PDOs to them).
7.3.10 0x608F Position_encoder_resolution
This read only object indicates the configured encoder increments per number of motor
revolutions. The information is read from the drive's encoder configuration.
7.3.11 0x6091 Gear_ratio
This object is used to apply scaling. When configured, appropriate user units can be
used to control the position of the shaft beyond a gearbox. The gear ratio is calculated
using the following formula:
gear ratio = motor shaft revolutions / driving shaft revolutions
Table 7.22 Supported profile units
Index Name
0x608F position_encoder_resolution
0x6091 gear_ratio
0x6092 feed_constant
Table 7.23 Position_encoder_resolution
0x608F Position_encoder_resolution
Sub-index 0
Access: RO Range: N/A Size: Unsigned 8 Unit: N/A
Default: 2
Description:
Sub-index 1
Access: RO Range: 0 to 0xFFFFFFFF Size: Unsigned 32 Unit: N/A
Default: 1
Description: Encoder increments
Sub-index 2
Access: RO Range: 0 to 0xFFFFFFFF Size: Unsigned 32 Unit: N/A
Default: 1
Description: Motor revolutions