A 6-axis robot arm is an industrial robot whose six rotary joints let it reach a point in its work envelope at any required angle. It is the most widely used robot type, from welding and painting to handling and assembly. In this article we explain what each axis does, why exactly six axes are needed and how to choose between 4, 5 and 6 axes.
The axes one by one
| Axis | Function |
|---|---|
| Axis 1 (base) | Rotates the whole robot around its base. |
| Axis 2 (shoulder) | Tilts the lower arm forward and back; lets the robot reach out. |
| Axis 3 (elbow) | Moves the upper arm up and down; sets height and reach together. |
| Axis 4 (forearm roll) | Rotates the forearm around its own axis. |
| Axis 5 (wrist pitch) | Bends the wrist up and down. |
| Axis 6 (flange roll) | Rotates the tool (torch, gripper) around its own axis. |
The first three axes decide where the tool is; the last three decide at what angle it is held.
Why exactly 6 axes?
The position and orientation of an object in space are defined by six values: three for position (X, Y, Z) and three rotation angles. A 6-axis robot can set all six independently, so it can approach any point in its reach at the required angle. That is what lets a welding torch meet the seam at the right angle or a spray gun stay perpendicular to the surface.
4, 5, 6 and 7 axes compared
- 4 axes: The tool always stays horizontal or vertical. Enough for palletising and simple pick and place; faster and cheaper.
- 5 axes: One rotational freedom is missing, so some angles are out of reach. Used for specific repetitive jobs.
- 6 axes: Reaches every angle; the standard for versatile work.
- 7 axes: An extra axis makes it easier to work around obstacles and in tight spaces. A linear track under the robot is also often called the “7th axis”.
How the robot calculates: inverse kinematics
You tell the robot “bring the torch to this point at this angle”; the controller calculates how many degrees each axis must turn. This calculation is called inverse kinematics. The same point can often be reached with more than one arm posture, and the controller picks one.
Singularity: When axes 4 and 6 line up, the robot cannot decide which of them to turn and tries to rotate them very fast. These postures are avoided during programming and cell design. Modelling the cell beforehand with kinematic analysis reveals such problems before production.
Choosing a 6-axis robot arm
- Payload: Tool and part weight, plus the moment at the wrist.
- Reach: The farthest point of the part must be reachable at the required angle.
- Repeatability: Critical for consistent welding and assembly.
- Cable and hose routing: Whether the torch cable runs through the wrist affects the risk of tangling.
- Protection class: Suitability for dust, spatter and water.
DKT robot arms
We configure our robot arms with 4 to 6 axes and 2 to 4 metres depending on the job, and either build them ourselves or source them. Every one gets our camera and laser-based machine vision system. On our AI welding robot the welder marks the weld spot with chalk; the robot recognises the mark, solves the inverse kinematics itself and welds.
Summary
- The first three axes set position; the last three set the tool angle.
- Six axes let the robot reach every point in its envelope at any angle.
- For simple pick and place and palletising, 4 axes can be enough.
- Singularities must be considered in cell design and programming.
How many axes do you need?
Send a photo of your part and the points the robot must reach; we will define axis count and reach together.
For our services see the industrial robot arm page; for robot types see what is an industrial robot?