Back to top

Touch Probe with the AKD EtherCAT drive

Touch Probe Overview

The touch probe feature of EtherCAT is simply a position capture.  In fact, it uses the position capture feature in the AKD.  When touch probe is set up and enabled, it automatically configures and arms the AKD’s position capture.  There are two touch probes available, corresponding to CAP0 and CAP1 in the AKD.  Each touch probe is configurable to use the positive edge, negative edge, or both.  There is a status word indicating the enable status of each Touch Probe and whether each edge has been triggered.

 image

image

Setup in EtherCAT (TwinCAT)

Objects 60B8 and 60D0 are used to configure touch probe.  Object 60B9 is the touch probe status, and objects 60BA – 60BD are the captured position values.

Object 60B8 – Touch Probe Function:

Object 60B8 sets the functionality of the touch probe feature.  It configures which touch probes are used and which edges can be triggered.

It can be configured to use one or two touch probes, and any or all of the four edges (positive and/or negative edge for each touch probe).

Object 60D0 – Touch Probe Source:

1 = Digital Input 1

2 = Digital Input 2

3 = Digital Input 3

4 = Digital Input 4

5 = capture trigger source 10 (Primary Index)

-1 = CAPx.TRIGGER = 0 (Digital Input 1)

-2 = CAPx.TRIGGER = 1 (Digital Input 2)

-3 = CAPx.TRIGGER = 2 (Digital Input 3)

-4 = CAPx.TRIGGER = 3 (Digital Input 4)

-5 = CAPx.TRIGGER = 4 (Digital Input 5)

-6 = CAPx.TRIGGER = 5 (Digital Input 6)

-7 = CAPx.TRIGGER = 6 (Digital Input 7)

-8 = CAPx.TRIGGER = 7 (RS485 Input 1)

-9 = CAPx.TRIGGER = 8 (RS485 Input 2)

-10 = CAPx.TRIGGER = 9 (RS485 Input 3)

-11 = CAPx.TRIGGER = 10 (Primary Index)

Simple Example:

1. Set object 60B8 = 27 (0x001B).  This sets the following bits:

  • Bit 0 = 1:  enable touch probe 1
  • Bit 1 = 1:  continuous trigger
  • Bit 3 = 1, Bit 2 = 0:  trigger source defined by 60D0
  • Bit 4 = 1:  enable sampling at positive edge of touch probe 1

2. Set object 60D0 subindex 1 = -1:  AKD digital input 1

When Touch Probe 1 is enabled, the status (object 60B9) will be 1 (0x0001).

When digital input 1 is turned on, the position is captured and the status (object 60B9) will be 3 (0x0003).

The captured position value can be read in object 60BA.

Since it is configured for continuous trigger, the status will remain 3 until Touch Probe 1 is disabled.

Position Scaling

The captured position values will correspond to the feedback position object 6063, and they have the same resolution as object 6063 based on object 608F sub1 (FB1.PSCALE).