The Pick-and-Place That Missed the Takt
We built a pick-and-place (a robot, article 52, picks a part from A, places at B). The takt (article 130) was 5 s. On the floor, the cycle took 7 s (too slow). The robot moved (it was fast). The problem: the robot waited (it had to wait for the input conveyor to present the part, and the output conveyor to clear). The robot’s motion was 3 s, but the waiting was 4 s. The cycle was 7 s. We parallelized (article 130): the robot picked the next part while the output conveyor moved. The waiting dropped to 1 s. The cycle was 4 s (under takt). The mistake was not parallelizing (the robot waited for the conveyors).
Pick-and-place cycle time sums the motion and the waiting. This article covers the optimization.
The Cycle (Motion + Wait)
A pick-and-place cycle has:
- Pick: The robot moves to A, the gripper (article 73) picks, the robot moves to B.
- Place: The robot places at B, the gripper releases.
- Wait: The robot waits for the input (part at A) or the output (B is clear).
The cycle = motion (3 s) + wait (4 s) = 7 s. The motion is fast (the robot). The wait is the bottleneck (the robot waits for the conveyors).
Step 1: The Input Buffer
Don’t let the robot wait for the input. Use a buffer (a conveyor that holds 2–3 parts). The robot always has a part to pick (no wait). The buffer presents the part (the robot picks immediately).
The pick-and-place rule: Parallelize (article 130). The cycle that missed takt had the robot waiting (4 s). Add an input buffer (the robot always has a part). Parallelize the output (the robot places while the conveyor moves). The wait drops.
Step 2: The Output Buffer
Don’t let the robot wait for the output. Use an output buffer (a conveyor that holds 2–3 parts). The robot places (the buffer takes it). The conveyor moves (later). The robot doesn’t wait for the conveyor to clear.
Step 3: The Gripper (Article 73)
The gripper’s pick/place time (the vacuum, article 73) adds to the cycle. A fast gripper (a quick vacuum, article 143) picks in 0.2 s. A slow gripper (a mechanical claw) takes 0.5 s. Use a fast gripper (for a fast cycle).
Step 4: The Robot Speed (Article 52)
The robot’s speed (article 52) affects the motion. A fast robot (6-axis, article 52) moves in 2 s. A slow robot (SCARA, for a plane) moves in 3 s. For a fast cycle, use a fast robot (or optimize the path, article 52).
| Step | Time |
|---|---|
| Robot motion (A to B) | 2 s |
| Gripper pick/place (article 73) | 0.4 s |
| Wait (input/output) | 4 s (before) |
| Wait (after parallel) | 1 s |
| Total (after) | 3.4 s (under 5 s takt) |
A Pick-and-Place Checklist
- What is the takt? (Article 130?)
- What is the cycle? (Motion + wait?)
- Is the robot waiting? (Input? Output?)
- Is there an input buffer? (2–3 parts?)
- Is there an output buffer?
- Is the gripper fast? (Article 73?)
- Is the robot fast? (Article 52?)
- Is it parallelized? (Article 130?)
- Does it meet takt? (Test?)
- Is the layout right? (Article 167?)
The Bottom Line
Pick-and-place cycle time reduces the wait (with buffers). The cycle that missed takt had the robot waiting. Add input/output buffers. Parallelize (article 130). The pick-and-place that met takt wasn’t the fastest robot — it had buffers.
