Each-picking robots are automated warehouse systems that pick individual products from bins, shelves, or totes and place them into customer orders. They matter because online retail often requires thousands of different items to be handled quickly, accurately, and safely. Unlike robots that move whole pallets or cases, each-picking robots must recognize and grasp single objects that vary in shape, size, texture, and weight.
This makes them a useful example of robotics, computer vision, mechanics, and logistics working together.
Key Facts
- Throughput = items picked / time, often measured in picks per hour.
- Cycle time = perception time + motion time + grasp time + place time + verification time.
- Pick accuracy = correct picks / total picks x 100%.
- Robot reach must cover the shelf bin, tote opening, and safe travel path.
- Payload limit must exceed item mass plus gripper mass, with a safety margin.
- Force balance for a stable vacuum pick: suction force must be greater than item weight, so F_suction > mg.
Vocabulary
- Each-picking
- Each-picking is the process of selecting one individual item at a time from storage and placing it into an order.
- End effector
- An end effector is the tool at the end of a robot arm, such as a suction cup, gripper, or soft robotic hand.
- Computer vision
- Computer vision is the use of cameras and algorithms to identify objects, estimate their positions, and guide robot motion.
- Path planning
- Path planning is the process of calculating a collision-free route for the robot arm or mobile platform to follow.
- Order tote
- An order tote is a container used to collect items that belong to a specific customer order or warehouse task.
Common Mistakes to Avoid
- Ignoring cycle time components: students often count only the arm movement time, but scanning, grasping, verification, and error recovery also reduce throughput.
- Assuming all items can use the same gripper: this is wrong because smooth boxes, soft bags, clear plastic, and irregular objects may need different grasping strategies.
- Forgetting payload safety margin: a robot that can barely lift an item may fail during acceleration because forces increase when the arm starts, stops, or changes direction.
- Treating pick accuracy as the same as speed: a faster robot is not better if it causes mispicks, damaged items, or extra human correction.
Practice Questions
- 1 A robot completes one pick in 9 seconds on average. What is its throughput in picks per hour?
- 2 A vacuum gripper lifts a 0.75 kg item. Using g = 9.8 m/s^2, what minimum suction force is needed just to balance the weight, before adding a safety margin?
- 3 A warehouse manager wants to increase robot speed by 20%, but fragile items are being dropped more often. Explain why acceleration, gripper force, and verification steps must be considered before changing the robot settings.