The Pick-and-Place That Missed the Takt: Cycle Time Budgeting
A pick-and-place cell with a 10-second cycle requirement. The actual cycle was 14 seconds. The customer needed 10 seconds. We didn’t buy a faster robot. We budgeted the cycle time and found 4 seconds of waste. This is how to analyze a cycle time that’s too slow.
The time budget
We timed every motion: pick (1.5 s), lift (0.5 s), move (3.0 s), place (1.0 s), retract (2.0 s), wait for downstream (6.0 s). Total: 14 seconds. The robot was waiting 6 seconds for the downstream conveyor to accept the part. That’s 43% of the cycle. The robot wasn’t the bottleneck — the downstream was.
| Motion | Original time | After optimization |
|---|---|---|
| Pick (gripper close) | 1.5 s | 0.8 s |
| Lift (Z axis) | 0.5 s | 0.3 s |
| Move (X-Y) | 3.0 s | 2.0 s |
| Place (gripper open) | 1.0 s | 0.6 s |
| Retract (Z + X-Y) | 2.0 s | 1.5 s |
| Wait for downstream | 6.0 s | 3.0 s (overlapped) |
| Total | 14.0 s | 8.2 s |
What we changed
1. Overlapped the wait. The robot waited 6 seconds for the downstream conveyor. We had the robot start its return move while the conveyor was still accepting. The robot doesn’t wait — it goes back to pick the next part while the conveyor cycles. The wait dropped from 6 to 3 seconds.
2. Faster gripper. The gripper took 1.5 seconds to close. We adjusted the flow control (faster close). It now takes 0.8 seconds. The gripper doesn’t need to close slowly — the part is in a fixture.
3. Faster move. The robot’s move was 3 seconds at 500 mm/s. We raised the speed to 800 mm/s (within the robot’s rating). The move dropped to 2 seconds. The acceleration was increased as well (S-curve). No vibration, no dropped parts.
4. Parallel the Z and X-Y. The robot lifted 0.5 s, then moved. We had the lift and move start simultaneously (a blended move). The lift and move overlap. The effective time drops to 0.3 s (the lift happens during the move).
The bottleneck analysis
The slowest station sets the cycle time. We measured every station. The downstream conveyor was the bottleneck at 6 seconds. We couldn’t speed it up (it was a fixed process). But we could overlap the robot’s motion with the conveyor’s cycle. The robot doesn’t wait — it moves while the conveyor runs.
The result
The cycle dropped from 14 to 8.2 seconds. The customer needed 10. We met it. We didn’t buy a faster robot. We didn’t change the downstream process. We overlapped motions and tightened the gripper timing. The takt time was a budgeting problem, not a hardware problem.
The cycle time rule: Time every motion. Find the wait (idle) time. Overlap motions where possible. Speed up the fastest motions (gripper open/close, Z lift) before speeding up the main move. The bottleneck isn’t always the robot — it’s often the wait for another station.
