User defined velocity units

Overview

The default unit for all velocity and speed data is rpm

The default unit for all acceleration and deceleration data is rpm/s

In the case that the application requires a higher precision in velocity, the unit can be configured by the user through object 0x60A9 SI unit velocity.

Supported values are:

  • 1 rpm (default value)

  • 0.1 rpm

  • 0.01 rpm

  • 0.001 rpm

Attention

As soon as this object is changed, all related objects and subitems also use the chosen unit and must be scaled accordingly. Unexpected behavior and accidents can occur if the chosen unit is not taken into account. For more information please refer to “Objects affected by changes of the velocity unit”.

Attention

Starting from firmware v5.0, the velocity reference frame is reported on the moving shaft. The target and actual velocity are scaled with a factor of “gear-ratio”. For better precision, it is recommended to change the SI unit to mrpm.

Usage

To configure the velocity unit write the following values through SDO to object 0x60A9 SI unit velocity:

  • 1 rpm (value 0x00B44700 or 0d11814656) - default

  • 0.1 rpm (value 0xFFB44700 or 0d4290004736)

  • 0.01 rpm (value 0xFEB44700 or 0d4273227520)

  • 0.001 rpm (value 0xFDB44700 or 0d4256450304)

Since version 19.​1.​0 of OBLAC Drives this can be done directly in the UI using Quick Open:

../../../../_images/OD_set_user_velocity2.png

After changing the unit please change all speeds /acceleration objects according to the new precision (see section below for details).

Click on “save to device” to keep the configuration.

Objects affected

  • 0x606B Velocity demand value

  • 0x606C Velocity actual value

  • 0x606D Velocity window

  • 0x606F Velocity threshold

  • 0x6080 Max motor speed

  • 0x6081 Profile velocity

  • 0x6083 Profile acceleration

  • 0x6084 Profile deceleration

  • 0x6085 Quick stop deceleration

  • 0x609A Homing acceleration

  • 0x60B1 Velocity offset

  • 0x60FA Control effort

  • 0x60FF Target velocity

These subitems are also affected by the value:

  • 0x6099:1 Homing speeds: Speed during search for switch

  • 0x6099:2 Homing speeds: Speed during search for zero

  • 0x2010:6 Torque controller: Field weakening starting speed

  • 0x2010:7 Torque controller: Field weakening ending speed

  • 0x2012:4 Position controller: Position loop integral limit

  • 0x2013:6 Gain scheduling: Position loop integral limit 0

  • 0x2013:15 Gain scheduling: Position loop integral limit 1

  • 0x2013:2 Gain scheduling: Threshold velocity 0

  • 0x2013:11 Gain scheduling: Threshold velocity 1

Example

When a dual-sensor setup is used with one encoder mounted after a reducer with a gear ratio of 1:100 the default velocity unit rpm causes severe inaccuracy in the motion control.

  1. In OBLAC Drives choose 0.001 RPM for SI unit velocity.

    When using a version of OBLAC Drives before 19.1.0, manually write 0d4256450304 to object 0x60A9 SI unit velocity through SDO. The terminal of OBLAC Drives can be used for this operation with the following code line:

ethercat download -p0 0x60A9 4256450304

  1. OBLAC Drives will automatically scale the affected objects.

Parameters

0x60A9 SI unit velocity

This object defines the velocity unit.

0x606B Velocity demand value

Output of position controller in position mode/trajectory generator in velocity mode.

0x606C Velocity actual value

Provides the value read at the velocity sensor (or the derivation of the position signal).

0x606D Velocity window

This value reflects each side of the target velocity.

0x606F Velocity threshold

Configures the velocity that is considered zero velocity.

0x6080 Max motor speed

Sets the maximum allowed speed for the motor in either direction.

0x6081 Profile velocity

Configures the velocity target for the end of the acceleration ramp during profiled motion.

0x6083 Profile acceleration

Configures the acceleration used during profiled motion.

0x6084 Profile deceleration

Configures the deceleration used during profiled motion.

0x6085 Quick stop deceleration

Deceleration used for stopping the motor when quick stop function is activated.

0x609A Homing acceleration

Configures the acceleration and deceleration to be used during a homing operation.

0x60B1 Velocity offset

Sets a feed-forward velocity as input to the velocity controller.

0x60FA Control effort

Provides a measure of the control effort (the output of the position control loop).

0x60FF Target velocity

Sets the target velocity and will be used as input to the trajectory generator.

0x2010 Torque Controller

Values Kp, Ki and Kd for Torque Controller

0x2012 Position Controller

Values Kp, Ki and Kd for Cascaded Position Controller (Both loops: Position and Velocity)

0x2013 Gain Scheduling

Parameters needed for Gain Scheduling