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Improving Placement Precision with a Re-Grasp Jig in Bin Picking

Use a jig to correct pick variability and ensure exact part presentation.

Context

In bin picking applications, the robot may not always grasp the part in the exact same location. Vision-based recognition and flexible pick parameters are designed for speed and robustness, but they can introduce small positional variations.

For downstream operations that demand high accuracy—such as CNC loading, assembly, or insertion tasks—these variations can compromise performance. A simple way to correct this is to use a re-grasp jig.

 

1. The Challenge

  • Initial picks are approximate: Vision systems and relaxed gripping settings allow successful bin picks, but grasp locations vary slightly.

  • Impact on accuracy: Inconsistent grasp leads to orientation or position errors when placing the part in fixtures, machines, or assembly jigs.

  • Solution needed: A method to reset the part into a consistent pose before final placement.

2. The Solution: Re-Grasp Jig

A re-grasp jig provides a physical reference that ensures repeatability.

How it works:

  1. Robot drops the part into a corner of the jig.

  2. The angled surfaces guide the part into a repeatable orientation.

  3. The part rests in a known and stable position.

  4. Robot picks the part again, now with perfect accuracy for the next step.

 

3. Design & Implementation Tips

When designing a re-grasp jig:

  • Angle: Use corner angles suited to the part’s geometry (commonly 90°).

  • Material: Choose durable, low-friction materials (e.g., hardened plastic, coated steel).

  • Mounting: Secure the jig to prevent shifts during repeated drops.

  • Clearance: Ensure the part can fall and align without bouncing or jamming.

  • Testing: Validate with multiple part samples to confirm reliability.

 

4. Throughput Considerations

Adding a re-grasp step increases cycle time. Use the following zones as a guideline:

  • Green zone: Feasible when cycle times allow for one additional step.

  • Yellow zone: Challenging—may require optimization to maintain throughput.

  • Red zone: Infeasible for very high-speed operations.

Tip: For certain part geometries, it may be possible to drop directly into the jig in a way that eliminates the need for a second pick, saving time.

 

5. Alternatives to Re-Grasp Jigs

For processes where throughput is critical and adding a jig step is not viable, consider software-based alternatives:

  • Force sensing (e.g., Machine Tending Copilot): Adjusts pick accuracy by detecting part position during handoff or placement.

  • Compliance tooling: Allows slight alignment corrections without requiring precise part presentation.

 

Conclusion

A re-grasp jig offers a simple, low-cost method to achieve precise part presentation in bin picking applications. While it introduces a cycle-time trade-off, it can significantly improve downstream reliability in assembly or machining tasks. For high-speed operations, software or compliance-based alternatives may be more suitable.