A robotic pick-and-place cell moves parts from a conveyor to another location such as a tray, box, machine, or second conveyor. The system must match the robot, end-of-arm tooling, conveyor speed, part spacing, and part orientation so every part can be picked reliably. Good tooling can increase throughput by lifting several parts at once, while poor tooling causes missed picks, collisions, and downtime.
This topic matters because modern factories use these cells to improve speed, consistency, safety, and product quality.
The main engineering challenge is timing: a robot has only a short window to detect, reach, grip, lift, move, and release each part. Sensors and encoders track conveyor motion so the robot can predict where the part will be when the gripper arrives. Vacuum cups, mechanical fingers, or magnetic grippers are selected based on part shape, surface, mass, stiffness, and spacing.
A well-designed cell balances cycle time, payload, reach, tooling weight, and part presentation to create a reliable automated process.
Key Facts
- Conveyor pitch is the center-to-center spacing between parts: pitch = conveyor speed x time between parts.
- Available pick time can be estimated by t = L / v, where L is the usable pick zone length and v is conveyor speed.
- Robot cycle time must be less than or equal to the time allowed per pick pattern: t_cycle <= t_available.
- Payload limit must include the parts plus the end effector: m_total = m_tool + m_parts.
- Vacuum holding force can be estimated by F = P x A, where P is pressure difference and A is cup area.
- Required lifting force must exceed weight with a safety factor: F_required >= SF x mg.
Vocabulary
- End-of-arm tooling
- The device attached to the robot wrist that grips, lifts, senses, or manipulates parts.
- Pick-and-place
- A robotic operation that picks up an object from one location and places it at another location.
- Conveyor pitch
- The distance from the center of one part to the center of the next part on a conveyor.
- Cycle time
- The total time required for the robot to complete one repeated pick-and-place operation.
- Part presentation
- The position, orientation, spacing, and visibility of parts as they arrive for robotic picking.
Common Mistakes to Avoid
- Ignoring the weight of the tooling when checking payload is wrong because the robot must carry both the gripper and the parts, not just the product.
- Using conveyor speed without considering part spacing is wrong because throughput depends on how often parts arrive, not only how fast the belt moves.
- Choosing vacuum cups only by part mass is wrong because surface texture, leakage, cup diameter, and acceleration also affect grip reliability.
- Assuming a stationary pick point on a moving conveyor is wrong because the robot must track where the part will be during the actual pick motion.
Practice Questions
- 1 A conveyor moves at 0.40 m/s and parts are spaced 0.20 m apart. How many parts pass the robot each second, and what is the time between parts?
- 2 A pick zone is 0.90 m long and the conveyor speed is 0.30 m/s. What is the maximum time a robot has before a part leaves the pick zone?
- 3 A robot misses picks when parts arrive tilted and randomly rotated. Explain two changes to the cell or tooling that could improve part presentation and gripping reliability.