External Reference Point Function; Overview

External Reference Point is a function that allows the robot to support part-to-process, wherein the robot is holding the part (like a weldment) and the welding torch is held stationary (stationary relative to to robot).  Possible applications include:

Arc Welding:  weldment is held by the robot, the welding torch is held fixed on a pedestal.  This could be used if the part is large and requires reorientation from weld-to-weld.

Spot Welding:  weldment is held by the robot, the spot welding gun is held fixed on a pedestal.  This could be used if the part requires reorientation from weld-to-weld, or if the existing (prior to robot integration) spot system is part-to-process, so the existing welding equipment could be used with minimal robot integration impact.

Additionally, Jogging-in-Teach reorientation of the weldment is very convenient, since you have the ability to rotate the entire part around the current welding location.

Dispensing:  part is held by the robot, and the dispensing head is stationary.  This could be used if the dispensing head is large/complex and difficult to be held by a robot.

Procedure

In order for the robot to move/rotate the part / weldment about the fixed mounted tool / torch / dispenser / etc.:

1. Create a TCP for the gripper or part you are holding
2. Teach a User Frame at the location of the fixed mounted tool.
3. A new set of instructions are created for this function: EIMOV

EIMOVL = linear motion

EIMOVC = circular motion

For each programmed step, you choose which User Frame the EIMOV instructions will consider.  You can program to multiple fixed mounted tools by using other User Frame #s.

Example:

An material handling robot holds a large cylinder w/ cap on end.  The intent it to rotate the part and weld the cap to the cylinder.  The robot places the cylinder/cap weld seam under the welding torch and rotates it under a fixed-mounted welding torch.  The robot manipulates the cylinder so that the weld joint (interface  between the cylinder and cap) stays under the welding torch

.

In order for the robot to move/rotate the cylinder correctly:

1. Create a TCP for the gripper to part you are holding.
2. Teach a User Frame at the location of the welding torch.  The origin is at the tip of the welding torch.
3. Program several EIMOVC instructions while rotating the part between each EIMOVC step.