What is Gripper Stroke?

In industrial automation and robotics, the "stroke" of a gripper refers to the total distance that the gripper jaws or fingers can move. Choosing the correct stroke is critical for ensuring that a robotic arm can successfully approach a part, grasp it securely, and release it without interference. If the stroke is too short, the gripper may collide with the part during approach; if it is too long, the gripper may be unnecessarily bulky or slow.

How to Calculate Required Gripper Stroke

The total required stroke is more than just the width of the part. To calculate the minimum necessary travel, you must account for the following variables:

• Nominal Part Width: The standard size of the object being handled.
• Part Tolerance: The maximum variation in the part's size. You must ensure the gripper can open wide enough for the largest possible part and close tightly enough for the smallest.
• Clearance: The air gap required between the gripper fingers and the part during the approach phase. This prevents scraping or accidental collisions.
• Grip Depth/Overlap: The distance the fingers must move inward to ensure a secure mechanical hold on the part.

Frequently Asked Questions

Why is safety clearance important?

Safety clearance accounts for minor positional inaccuracies in the robot arm. Without sufficient clearance, even a slight misalignment could cause the gripper to strike the part, potentially damaging the equipment or the workpiece.

Should I choose a pneumatic or electric gripper?

Pneumatic grippers are typically "all or nothing" in their stroke, meaning they move to full open or full closed positions. Electric grippers often allow for programmable stroke lengths, which can save cycle time by only opening as wide as necessary for the specific part being handled.

How does internal vs. external gripping affect the calculation?

The tool above focuses on external gripping. For internal gripping (expanding inside a hole), the logic is reversed: your stroke must allow the fingers to contract enough to enter the hole and expand enough to maintain high friction against the inner walls.