Frames
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Frames are what allow us to use mathematical expressions to define motion and positions in the real world.
Coordinate Systems
Joint
The joint coordinate system is the simplest from the point of design and control. Each joint has a specific range of motion it is capable of, expressed in degrees. A joint coordinate is simply a list of each joint's angular position.
The robot controller processor calculates the end of arm tooling point using simple trigonometric equations, with the variables of each joint's angle and length between joints.
Saving global positions in JOINT coordinate systems make them truly global, as it will always represent an exact configuration of the robot arm.
| Joint 1 | Joint 2 | Joint 3 | Joint 4 | Joint 5 | Joint 6 |
|---|---|---|---|---|---|
| 100° | 112.323° | 10° | 88° | 399° | 84.34° |
Cartesian
| X | Y | Z | Yaw | Pitch | Roll | Configuration |
|---|---|---|---|---|---|---|
| 100mm | 112.323mm | 300mm | 108° | 20° | 84.34° | N, U, B |
In the bridge between computation and the physical world, we have to have some sort of reference to begin our measurements. Each point in space can be represented by three values represented by the characters X, Y, and Z. This is known as a "Cartesian" coordinate system.
To use a Cartesian system we have to define where 0 is for each axis. Since it does not affect the calculations and only makes it easier to understand, we define 0 as the same point for all 3.
The familiar looking image on the left demonstrates this. The intersection between the three axis lines is the "Zero" point.
There are three more axes to consider, but don't define the object's location in space. They are represented by the characters W, P, and R, colloquially referred to as yaW, Pitch, and Roll.
Yaw, Pitch, and Roll determine the object's orientation about the position defined in X, Y, and Z.
| Position | Symbol | Description | Our Robot's WORLD frame |
|---|---|---|---|
| X Coordinate | X | Distance along X axis from the origin point | Forward/Back |
| Y Coordinate | Y | Distance along Y axis from the origin point | Left/Right |
| Z Coordinate | Z | Distance along Z axis from the origin point | Up/Down |
| Orientation | Symbol | Description |
|---|---|---|
| Yaw | W | Rotation about the X axis |
| Pitch | P | Rotation about the Y axis |
| Roll | R | Rotation about the Z axis |
The FANUC Cartesian coordinate system also includes data that represents the configuration of various joints, since there is often more than one solution to bring the tool to a specific point and orientation. This is described as Wrist, Elbow, and Robot.
| Configuration | Symbols | Description |
|---|---|---|
| Wrist | N/F | |
| Elbow | U/D | |
| Facing | T/B |
Frames
The choice of frames in FANUC programming determine where to reference "zero" at for each axis. It can be useful to work with your robot in reference to the tool, or your work area, or the robot itself.
World Frame
The world frame is the default for your robot. The zero point for X, Y, and Z is the center of the robot's J1 axis, at the height of J2.
User Frame
When working with a robot, it is often desirable to align the cartesian axes with your intended work area. This may be at a different position or angle than the base of the robot (World Frame) so the option of User Frames is used.
In user frames, the coordinates you work with start at a user-defined position and the axis directions are determined by the user. Using the three-point method for teaching user frames, the zero "origin point" is taught, as well as the direction of the X and Y axes.
X, Y, and Z remain at right angles to one another but their positive directions from the newly defined origin are chosen.
As an example, a robot may have a conveyor bringing products into its work envelope. This conveyor may be at an arbitrary position relative to the robot, at an angle, or at a unique height in reference to the world frame. Teaching a user frame allows you to jog the robot in a way that is perfectly aligned with that conveyor, as well as teach points on the conveyor that are in reference to permanent marks on the conveyor's chassis. This allows those taught points to still be useful and accurate, even if the conveyor's position, height, and orientation is changed - just by redefining where the new position and orientation are.
User Frame 0 is permanently set to be equivalent to the robot's WORLD frame.
Methods
Three point
In the three-point method for teaching user frames, you teach an origin point to determine the zero point for each axis, an X point to determine the exact direction of positive X, and a Y position to determine the direction of positive Y.
There is a lab available detailing all the steps involved in using the three-point method, User Frame Lab
Six-Point (XZ)
Six-Point (XY)
Two-Point + Z
Four-Point
Direct Entry
The direct entry method requires you to know the exact world-frame coordinates of your zero point, as well as the orientation of each axis. They can be entered manually, one at a time.
Tool Frame
The robot is a collection of axes that each have a specific range of motion and distance from one another. The processor calculates the position of the robot’s Tool Center Point (TCP) by the angle of each axis and the known distance to the next.
By default, FANUC robots calculate position in the real world by the center of the plate on the end of the last actuator. When you attach a tool, you must tell the robot where the effective end of the tool is, relative to the tool center plate.
Three point
In the three-point method for teaching tool frames, you align the exact center of the tool's effective end with a reference point (any pointy object) three times, each at significantly different orientations. Using these three approach points, the controller will calculate the location you used, relative to the tool center plate.
There is a lab available detailing all the steps involved in using the three-point method, Tool Frame Lab
Six-Point (XZ)
Six-Point (XY)
Two-Point + Z
Four-Point
Direct Entry
The direct entry method requires you to know the exact coordinates of your tool's center point in reference to the tool plate, as well as the orientation of each axis. They can be entered manually, one at a time.
Jog Frame