Offsets/Frames Tab Reference
- Daniel Rogge
- Amanda Lucas
About Coordinate Frames/Offsets
Coordinate system frames in robotics are similar to coordinate system offsets in a CNC machine. A frame is a way to change what physical position the robot will move to when it is commanded to go to, for instance, [0, 0, 0, 0, 0, 0].
There are three commonly used robot frame types: the base frame, user frames, and tool frames.
Base Frame
The base frame is located near the base of the robot and is not adjustable. You can think of the robot’s base frame like you would a milling machine’s G53 coordinate location. It’s the machine’s view of the world, onto which other frames are applied.
User Frames
Like the G54, G55, etc. work offsets in the CNC world, robot user frames exist to make robot programming easier. A user frame allows you to align the robot's XYZ coordinate system around a fixture or workpiece that may be translated and/or rotated with respect to the base frame of the robot.
For example, say you want to program the robot to draw a line drawing on a whiteboard. Most CAM programs will output X and Y positions with an occasional Z retract move. That works fine for the robot, unless the whiteboard is tilted at an angle relative to the base of the robot. A user frame can accommodate that angle, as well as any XY or Z offset that you might want to apply. Work offsets on a 3-axis CNC machine involve X, Y, and Z values, but user frames on a robot also include A, B, and C values for a total of 6 offsets.
It’s important to note that the robot has two different ways to interpret and move to a position. Robot waypoints can either be cartesian ([X, Y, Z, A, B, C]) or they can be “joint” ([J1 angle, J2, J3, J4 ,J5, J6]). Any cartesian waypoint may be affected if the user frame changes. Joint-type waypoints remain the same regardless of a change to the active user frame.
Because most CAM programs output X, Y, Z, and occasionally A, B, and C coordinates, any CAM-generated robot program will use a user frame.
Tool Frames
Milling machines have tool offsets, which are usually a Z-only value equal to the length of the tool as measured from the spindle nose to the tool tip. Lathe tools have both X and Z offsets. A robot tool frame has 6 possible offsets, making it more complex to understand than a simple milling machine tool offset.
The simplest tool frame involves a tool that is concentric to the end effector, like the Sharpie holder shown in the quick tip video. Such a tool frame has only a Z offset.
A tool like the deposition tool shown in the picture above may require a frame with multiple offsets including one or more rotations (A, B, C offsets).
Unlike a CNC mill, where tools can be measured offline using a pre-setter, robot tool frames almost always need to be taught on the robot.
Frames/Offsets Notebook
The Frames tab of the main notebook contains a notebook of its own, consisting of three sections: