The Robot That Couldn’t Reach the Conveyor: Work Envelope and Layout, Not the Robot
A 6-axis robot picking parts from a conveyor. The conveyor was placed at the edge of the robot’s work envelope. The robot could reach, but it was at the wrist joint’s extreme angle. The wrist twisted. The path was awkward. The customer thought the robot was too small. The robot was fine. The layout was wrong. This is about robot work envelope planning, not about the robot being undersized.
The work envelope
Every robot has a work envelope — a 3D volume where it can reach. The envelope is defined by the reach (max distance from base to wrist). For a 6 kg robot with 900 mm reach, the envelope is a 900 mm sphere around the base. But at the edges of the envelope, the wrist is at an extreme angle. The robot can reach, but it’s not comfortable — the wrist twists, the cycle time increases, and there are singularities (points where the robot loses a degree of freedom).
The placement rules
| Rule | Why |
|---|---|
| Keep targets within 70-80% of max reach | Avoids wrist extremes |
| Keep the robot centered on the work area | Even reach in all directions |
| Keep the wrist angle within ±45° | Avoids singularities |
| Allow clearance for the gripper and cables | Don’t hit the robot on itself |
| Check the overhead reach (above the base) | The envelope is smaller overhead |
What we did
1. Moved the conveyor closer. The conveyor was at 850 mm from the robot base (near the 900 mm max reach). We moved it to 650 mm. The robot now reaches comfortably (72% of max reach). The wrist angle is normal. The path is smooth.
2. Re-oriented the robot. We rotated the robot 90 degrees. The conveyor is now in front of the robot (not to the side). The arm reaches straight out. The wrist doesn’t twist. The cycle time dropped by 1 second.
3. Used the robot’s software to check. We used the robot’s offline programming software to simulate the path. The software showed the wrist angle at every point. We confirmed all targets are within the comfortable envelope. No surprises during commissioning.
The robot wasn’t too small
The robot’s 900 mm reach was enough for the 850 mm distance. But “enough” isn’t “comfortable.” At the edge of the envelope, the robot fights itself. The fix was layout, not a bigger robot. We saved $15,000 by not upsizing.
The robot placement rule: Keep work within 70-80% of max reach. Center the robot on the work area. Check the wrist angles in simulation. A robot at the edge of its envelope is slow, awkward, and prone to singularities. The robot that couldn’t reach the conveyor wasn’t too small — it was poorly placed.
