Touch Probe

With the Touch Probe feature of EtherCAT, a drive captures the position of a motor encoder when a discrete input signal edge is detected on the drive. Touch Probe is used for homing and registration with EtherCAT drives. The touch probe operates in the drive itself and is not affected by any communications delays.

The RMC supports 2 touch probes as defined by the CiA402 drive specification, meaning that two individual position captures in a drive can be kept track of simultaneously.

Touch Probe and Homing Modes

The RMC200 EtherCAT supports homing of drives only via touch probe. It does not support other CiA402 homing modes that are built into the drive.

RMC User Programs can be used together with the touch probe to create the desired motion profiles and logic for homing.

For more details, see Homing with Touch Probe below.

Touch Probe Sources

The touch probe input may come from any of these 3 sources:

Physical touch probe input

The drive may have one or two dedicated touch probe inputs.
Encoder Index (Z or Zero Impulse)

When the drive senses the encoder index pulse, it can trigger the touch probe position capture.
Source Selected by Object 0X60D0

This provides for selection in the drive of other homing sources, such as general-purpose inputs. The source for the touch probes are defined by object indexes as follows:
- Touch Probe 1: object 0X60D0, sub-index 1 (0X60D0:01)
- Touch Probe 2: object 0X60D0, sub-index 2 (0X60D0:02) (if supported by the drive)

Setting up Touch Probe

These steps apply to setting up the touch probe for either homing or registration.

Set up the Drive

Wire the physical touch probe input of the drive (unless using the encoder index). Make any necessary settings in the drive, such as defining which input will be used, input polarity, etc.
Define an Axis

In the Axis Definitions, create a Control axis for the drive.

Set up the PDO Mapping

In RMCTools, in the EtherCAT Editor, select the drive. On the PDO Mapping tab, add the following entries to the PDO data:

Required:
Touch Probe Function	0x60B8
Touch Probe Status	0x60B9
As needed (at least one):
Touch Probe Positive Position 1	0x60BA
Touch Probe Negative Position 1	0x60BB
Touch Probe Positive Position 2	0x60BC
Touch Probe Negative Position 2	0x60BD

Set the Touch Probe Object Indexes in the Axis Parameters

The Input SubDevice axis parameter must first have been set to the desired EtherCAT drive.

In the Axis Parameters, on the All tab, expand Feedback, then Registration/Homing. Make sure the touch probe parameters are set as follows:

Touch Probe Function Index	0x60B8
Touch Probe Status Index	0x60B9
Touch Probe Positive Position 1 Index	0x60BA
Touch Probe Negative Position 1 Index	0x60BB
Touch Probe Positive Position 2 Index	0x60BC
Touch Probe Negative Position 2 Index	0x60BD

Typically, you will not use all the touch probes. Any unused Touch Probe Index axis parameters will be red. This is not an error, but simply indicates that they are not mapped in the PDO of the selected Output Device.

Homing with Touch Probe

After setting up the touch probe functionality as described in Setting up Touch Probe above, homing can be performed as follows.

Choose the Arm Home (50) command

Configure the parameters as follows:
1. Home Pos:
  
  Set this to the desired position that the axis should be set to when the homing trigger occurs.
2. Trigger Type:
  
  Choose whether the homing should occur on the rising or falling edge of the signal.
3. Repeat Mode:
  
  The only option is Single(0). The homing will occur once.
4. Home Input:
  
  Choose the source of the signal that will trigger the homing:
  1. TP 1 In: use the dedicated touch probe input 1 on the drive
  2. TP 1 Z: use the index pulse, for touch probe 1
  3. TP 1 Object: use object 0X60D0:01 in the drive to specify the source
  4. TP 2 In: use the dedicated touch probe input 2 on the drive
  5. TP 2 Z: use the index pulse, for touch probe 2
  6. TP 2 Object: use object 0X60D0:02 in the drive to specify the source
Send the Arm Home (50) command
Monitor the homing bits

In the Axis Status Registers, on the All tab, expand Home.

Once the Arm Home (50) command is sent, the Home Armed status bit will be set. When the specified home trigger occurs, the Home Armed status bit will be cleared, the Home Latched status bit will be set, and the Actual Position will have been updated with the specified Home Position.
Creating a homing routine

You can create any desired homing routine in a user program. For example, you can create a user program that:
1. Moves in the negative direction until it senses the negative travel limit.
2. Arms the home, using the encoder index as the touch probe source.
3. Moves in the positive direction at a slower speed until the Home Latched bit is set indicating that the axis homed (because the encoder Index pulse was reached).
This is just one example of many possible homing procedures.

Registration with Touch Probe

After setting up the touch probe functionality as described in Setting up Touch Probe above, registration can be performed as follows.

Choose the Arm Registration (52) command

Configure the parameters as follows:
1. Registration Number:
  
  Choose which registration this will apply to, either 0 or 1.
2. Registration Input:
  
  Choose the source of the signal that will trigger the registration:
  1. TP 1 In: use the dedicated touch probe input 1 on the drive
  2. TP 1 Z: use the index pulse, for touch probe 1
  3. TP 1 Object: use object 0X60D0:01 in the drive to specify the source
  4. TP 2 In: use the dedicated touch probe input 2 on the drive
  5. TP 2 Z: use the index pulse, for touch probe 2
  6. TP 2 Object: use object 0X60D0:02 in the drive to specify the source
3. Input Edge:
  
  Choose whether the homing should occur on the rising or falling edge of the signal.
Send the Arm Registration (52) command.
Monitor the registration bits

In the Axis Status Registers, on the All tab, expand Registration.

Once the Arm Registration (52) command is sent, the Registration 0 Armed or Registration 1 Armed status bit will be set. When the specified registration trigger occurs, the corresponding Registration Armed status bit will be cleared, the corresponding Registration Latched status bit will be set, and the corresponding Registration Position will have been updated with the captured position.

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