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Assigning EtherCAT Data to Axes

After creating a new EtherCAT network, which consists of physically connecting the devices, creating the network in RMCTools, and configuring the SubDevices, the next step is to assign EtherCAT data from those SubDevices to axes.

Assigning EtherCAT data to axes involves the following main steps:

  1. Define Axes to use EtherCAT

    Define axes to use EtherCAT for the output, primary feedback, and/or the secondary feedback (if the axis is dual-loop).

  2. Set Axis Parameters to Specify EtherCAT Data

    Set the Axis Parameters to specify which SubDevice and which data in the SubDevice to use for each portion of the axis that is defined to use EtherCAT data (output, feedback, secondary feedback).

  3. Set Scaling Parameters for the EtherCAT Data

    All EtherCAT axis output and feedback values must be scaled via the axis parameters.

Defining Axes to Use EtherCAT

Mixing and Matching Axis Component Assignment

Each component of an axis (output, feedback, and secondary feedback) can be individually assigned to use physical I/O modules on the RMC, EtherCAT data, or custom feedback.

Typically, an axis that uses EtherCAT will use EtherCAT for all output and feedback components, but you can mix and match to suit your specific application. For example, an axis may use EtherCAT for the output and feedback or use EtherCAT for only the output and use an RMC200 I/O module, such as the S8 module, for the feedback.

An exception to the flexibility of mixing and matching output and feedback source types is axis that use an EtherCAT drive in Cyclic Synchronous Position (CSP) mode, which must use EtherCAT for both the output and position feedback.

Local Control and Remote Control

When defining axes on an RMC200 that includes an EtherCAT module, all control axes will be either Local Control or Remote Control. Remote Control is specifically for drives in CSP mode. All other control axes are Local Control.

A Local Control axis performs the main PID calculation in the RMC, whereas for a Remote Control axis, the main PID (position) calculation is performed in the drive.

For more details, see Axis Type: Remote Control.

How to Define an Axis to Use EtherCAT

To define an axis to use EtherCAT for one or more of the output or feedback components:

  1. In the Axis Definitions dialog, click New.

  2. Choose the axis type (control, reference, or cascading) and click Next.

  3. For control axes:

    1. Choose Local Control, unless the axis is for a drive in CSP mode, in which case choose Remote Control. Click Next.

    2. On the Control Axis page, choose the number of control loops and the feedback types for each loop, then click Next.

  4. For reference axes:

    1. On the Reference Axis page, the feedback type, then click Next.

  5. On the Hardware Assignment page:

    1. Choose the channel for each output and feedback component of the axis. This may be the EtherCAT module, an I/O module on the RMC, or custom.

    2. For I/O modules, choose the specific input or output on the module.

    3. For EtherCAT, choose whether the component is from a motor drive, valve, or a generic device. A generic device is any device that is not a CiA402 drive or a CiA408 valve.

      It is important to choose the correct option!

      For EtherCAT drives, the Control Output must be set to Drive. The Position input will often be Drive to indicate the position is from the drive’s encoder,but it is possible to use an external EtherCAT position sensor, in which case the selection will be Generic.

      For EtherCAT valves, the Control Output must be set to Valve. The Position and Pressure or Force inputs will always be Generic, even if they are sensors wired directly to the EtherCAT valve.

  6. Click Finish.

Setting the Axis Parameters for EtherCAT

Once an axis has been defined to use EtherCAT, in the Axis Tools, use the Axis Parameters to define which EtherCAT data each component of the axis will use.

The data must first have been included in the PDO Mapping. Any Index axis parameters that remain red indicate that the data doesn’t exist, and it must be included in the PDO mapping.

Specifying the SubDevice and Indexes

For each output and feedback component of the axis, the main steps are:

  1. Select the SubDevice

  2. For each related axis parameter, select a specific data item within that SubDevice by specifying the Index of the data item.

    For drives and valves, many of the EtherCAT-related axis parameters are already set to default values, because the CiA402 and CiA408 specifications define those index values.

  3. Set the Scaling for the input and output values.

Specific instructions are provided below for the Control Output, Primary Feedback, and Secondary Feedback components of an axis.

Control Output

To specify the EtherCAT data for the Control Output component of the axis:

  1. In the Axis Parameters, select the Setup tab.

  2. In the Primary Control Setup section, click the Output SubDevice cell for the axis, then click the button.

  3. In the SubDevice box, choose the desired SubDevice. Only the SubDevices with outputs will be listed in the SubDevice box. Click OK.

  4. Set additional axis parameters based on the EtherCAT output device type:

    Drives (CiA402) with Remote Control mode (CSV or CST):

    Set Drive Output PID Mode to Velocity Output (CSV) or Torque Output (CST mode). Velocity Output is the most commonly used.

    Set the following Indexes:

    Note: For multi-axis drives, these indexes are usually incremented by 0x800 for each axis. For example, the axis 1 Control Word Index in the drive would be 0x6840:00 and axis 2 Setpoint Index would be 0x7040:00.

    Drives (CiA402) with Local Control mode (CSP):

    Note: For multi-axis drives, these indexes are usually incremented by 0x800 for each axis. For example, the axis 1 Target Position Index would be 0x687A:00 in the drive and axis 2 setpoint Index would be 0x707A:00.

    Valves (CiA408):

    Generic:

Control Output Scaling

An RMC axis’ output value, whether a Control Output or a Target Position, is a 32-bit floating point value. EtherCAT drives, valves, and analog outputs typically use integer values, and have various ranges. Therefore, the output of an EtherCAT axis must be scaled.

Set the output scaling based on the EtherCAT output type:

Drives (CiA402) in CSV mode:

To convert the RMC’s Control Output to a velocity command value that the EtherCAT drive can accept:

  1. Set the Velocity at 100% Output. This means that when the RMC sends a 100% Control Output signal, the drive will be commanded to move at this velocity. To set this parameter, determine the maximum speed that you wish to command the drive and use that value.

  2. Set the Velocity Scale. To calculate this parameter, consult the manufacturer’s documentation to determine the value that corresponds to 100% velocity. Then, divide the Velocity at 100% Output by that value.

Drives (CiA402) in CST mode:

To convert the RMC’s Control Output to a torque command value that the EtherCAT drive can accept:

  1. Set the Torque at 100% Output. This means that when the RMC sends a 100% Control Output signal, the drive will be commanded at this torque. To set this parameter, determine the maximum torque that you wish to command the drive and use that value.

  2. Set the Torque Scale. To calculate this parameter, consult the manufacturer’s documentation to determine the value that corresponds to 100% torque. Then, divide the Torque at 100% Output by that value.

Drives (CiA402) in CSP mode:

No output scaling is required.

Valves (CiA408):

To convert the RMC’s Control Output to a command value that the valve can accept:

  1. Set the Output Type to Counts Bi for a typical 4-way proportional valve. If the valve is 3-way, choose Counts Uni.

  2. Set the Output at 100%, Output at 100% and Output at 100% axis parameters as follows:

      Output at 100% Output at 0% Output at -100%
    ATOS 16,384* 0 -16,384*
    Bosch 100,000 0 -100,000
    Moog 16,384 0 -16,384
    Parker 16,384 0 -16,384

    *ATOS can support 100,000 to -100,000 if the VDMA version is changed from 1.5 to 1.6 using the ATOS configuration software, or setting the ATOS-specific object 0x220D.

Generic:

  1. Set the Output Type to Counts Bi for a bidirectional (±) analog output signal. For a unidirectional analog output signal, choose Counts Uni.

  2. Consult the manufacturer’s documentation and set the Output at 100%, Output at 0%, and Output at -100% axis parameters accordingly.

Primary Feedback

To specify the EtherCAT data for the Primary Feedback component of the axis:

  1. In the Axis Parameters, select the Setup tab.

  2. In the Primary Control Setup section, click the Input SubDevice cell for the axis, then click the button.

  3. In the SubDevice box, choose the desired SubDevice. Only the SubDevices with inputs will be listed in the SubDevice box. Click OK.

  4. Click the Counts Index cell for the axis, then click the button.

  5. In the Variable box, choose the desired feedback object, then click OK.

    The feedback object for CiA402 drives is typically 0x6064:00 (position actual value). For other devices, the feedback object varies significantly by manufacturer.

  6. For devices such as EtherCAT encoders, you may wish to set the No Transducer Index so that an error in the encoder will be reflected in the RMC’s axis No Transducer Status bit. Consult the manufacturer documentation to determine which bit provides this information.

    1. In the Axis Parameters, select the All tab.

    2. In the Feedback section, click the No Transducer Index cell for the axis, then click the button.

    3. In the Variable box, choose the desired object. In the Bit number box, choose the bit that corresponds to a feedback OK or not OK logic. Click OK.

    4. Set the No Transducer Polarity axis parameter to indicate the logic of the bit you selected:

      Active High: a transducer error exists if the bit is on.

      Active Low: a transducer error exists if the bit is off.

Primary Feedback Scaling

Setting the Scale and Offset parameters for EtherCAT feedback is very similar to setting the scale and offset for any feedback. The preferred method is to use the Scale/Offset Wizards in the Axis Parameters. See Scaling Overview for details.

Secondary Feedback

To specify the EtherCAT data for the Secondary Feedback component of the axis:

  1. In the Axis Parameters, select the Setup tab.

  2. In the Secondary Control Setup section, click the Input SubDevice cell for the axis, then click the button.

  3. In the SubDevice box, choose the desired SubDevice. Only the SubDevices with inputs will be listed in the SubDevice box. Click OK.

  4. Click the Counts Index cell for the axis, then click the button.

  5. In the Variable box, choose the desired feedback object, then click OK.

    The feedback object varies by manufacturer and axis types.

    For dual-input force, perform these steps for both Input SubDevice A and Input SubDevice B, along with Counts Index A and Counts Index B.

Secondary Feedback Scaling

Setting the Scale and Offset parameters for EtherCAT feedback is very similar to setting the scale and offset for any feedback. The preferred method is to use the Scale/Offset Wizards in the Axis Parameters. See Scaling Overview for details.

 

See Also

Creating a New EtherCAT Network | EtherCAT Overview

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