The Robot That Couldn’t Reach the Conveyor
We laid out a robot cell: a 6 kg robot on a stand, a conveyor for parts, and a machining fixture. On the layout, the robot’s reach covered everything. On the floor, the robot couldn’t reach the far end of the conveyor. The conveyor was 1.4 m from the robot base. The robot’s reach was 1.4 m — right at the limit. With the gripper extending 100 mm, the reach was 1.5 m, but at the far end the arm was fully extended and had no wrist angle left. The parts were at the edge of the work envelope. We moved the conveyor 200 mm closer. The robot reached comfortably. The mistake was putting the part position right at the edge of the robot’s reach, not leaving margin.
Robot work cell layout is about the robot’s reach, the work positions, and operator access. Get it wrong, and the robot can’t reach everything. This article covers the layout.
The Robot Work Envelope
Every robot has a work envelope (the volume it can reach). The datasheet shows it as a diagram. The envelope is not a sphere — it’s a complex shape (the robot’s arm can reach some areas better than others).
Key points:
- Maximum reach: The farthest distance the wrist can reach (from the robot base center).
- Best work zone: The area in front of the robot, at about 50–80% of the maximum reach. The arm is bent (not fully extended). This is where the robot is strongest and most accurate.
- Dead zone (behind the robot): The robot can’t reach behind its own base.
Put the work positions in the best zone (50–80% of max reach). Don’t put them at 100% (the edge).
Step 1: List All Work Positions
Before laying out the cell, list every position the robot must reach:
- Pick point 1 (conveyor).
- Place point 1 (fixture).
- Pick point 2 (feeder).
- Place point 2 (output conveyor).
- Tool change position (if multiple tools).
- Home position.
Measure each position’s distance from the robot base. All should be within the robot’s reach — and in the best zone (50–80% of max).
Step 2: Leave Margin
Don’t put a work position at 100% of the robot’s reach. The robot’s accuracy drops at full extension (the arm is straight, wrist moment is high, article 59). Leave 10–20% margin.
If the robot’s max reach is 1.4 m, put work positions at 1.0–1.2 m. The arm is bent, and the wrist has room to angle.
The robot that couldn’t reach had the conveyor at 1.4 m (100% of reach). Move it to 1.1 m (78% of reach). The robot reaches comfortably.
The layout rule: Put all work positions at 50–80% of the robot’s maximum reach. Not at 100%. The robot that couldn’t reach had the conveyor at the edge of its envelope. Move it in. The robot works best when its arm is bent, not fully extended.
Step 3: Operator Access
The cell is fenced (article 74). But the operator needs access (to load parts, clear jams, service). Layout the operator’s access:
- Loading station: The operator loads raw parts from outside the fence (through a loading opening or on a conveyor).
- Unloading: Finished parts exit on a conveyor.
- Service access: A gate for maintenance (interlocked).
- E-stop: Accessible from all sides.
The operator shouldn’t need to enter the cell for normal operation. Entry is only for maintenance or jam clearing.
Step 4: Safety Distance
The fence is placed at the safe distance from the robot (article 74). The robot’s maximum reach plus the safe distance determines the fence position.
The work cell layout must fit within the fence. If the robot’s reach is 1.4 m and the safe distance is 0.8 m, the fence is at least 2.2 m from the robot base. The entire cell (conveyors, fixtures) fits within that.
Layout Considerations
- Conveyor direction: Parts enter from one side, exit from another. The robot picks and places between them.
- Fixtures: The machining/assembly fixtures are in the robot’s best zone.
- Cable management: The robot’s dress pack (cables) needs room to move without snagging.
- Lighting: If there’s vision, the light is mounted so the robot doesn’t block it.
- Spare parts / tools: Keep space for a tool rack (if the robot changes grippers).
| Layout Element | Consideration |
|---|---|
| Robot base position | Centered between pick and place points |
| Work positions | 50–80% of max reach (best zone) |
| Operator access | Loading/unloading from outside the fence |
| Fence position | At safe distance S = K × T from max reach |
| Cable dress pack | Room to move without snagging |
| Tool rack | Within reach for tool changes |
Simulation (Offline Programming)
Before building the cell, simulate the layout offline (using the robot’s simulation software). Import the robot, the conveyors, and the fixtures. Check that the robot reaches every position without collision.
The simulation catches layout problems (a conveyor in the way, a position at the edge of reach) before the cell is built. Fix it in the software, not on the floor.
A Work Cell Layout Checklist
- What is the robot’s max reach? (From the datasheet.)
- List all work positions (pick, place, home, tool change).
- Is each position within reach? (With margin?)
- Are positions in the best zone? (50–80% of max?)
- Does the robot’s arm clear all obstacles? (No collisions?)
- Operator access? (Loading/unloading from outside?)
- Fence at safe distance? (Article 74.)
- E-stop accessible from all sides?
- Cable dress pack room?
- Tool rack within reach? (If applicable.)
- Vision lighting not blocked?
- Simulated offline? (No surprises on the floor?)
The Bottom Line
Robot work cell layout puts the work positions in the robot’s best zone (50–80% of max reach). The robot that couldn’t reach had the conveyor at 100% of its envelope. Move it in. Leave margin for the wrist angle and cable dress pack. Lay out operator access from outside the fence, and place the fence at the safe distance. Simulate the cell offline before building. The cell where the robot reaches everything comfortably wasn’t the largest robot — it was laid out in the best zone.
