Charge Builds Where the Robot Touches the Part
The triboelectric pair you built into the tooling
Every time a vacuum cup lifts off a plastic housing, the two surfaces separate and charge is left behind. A bare elastomer cup against a moulded polymer part is a strong pair, and cycle rates on an automated cell mean the separation happens thousands of times per shift. The result is a part that arrives at the next station carrying charge despite sitting on a grounded mat.
The fix is at the interface. Conductive elastomer cups and dissipative gripper pads give the charge a path off the part as it is released, rather than letting it accumulate until the part touches something that can arc. Adhesive tape used to hold parts on a fixture belongs in the same review — ordinary tape is an excellent charge generator and a poor conductor.
The ground path has moving joints in it
A grounded robot base does not make the end effector grounded. Slip rings, cable carriers and rotating joints all interrupt continuity, and a tool changer is a deliberate break in the path. Check continuity from the pad or cup body to the machine earth with the tool in its working position, not with the arm parked.
Ionisation is the practical complement where contact cannot be made conductive — for example plastic parts that must be handled by their cosmetic surfaces. Mount the ioniser where the part actually rests before the next operation, and verify balance at the part position, not at the nozzle. A bar that reads perfect at the outlet but is 400 mm from the part is not neutralising anything.
FAQ
Why do parts arrive charged when the cell has ESD mats?
Mats ground what they touch. Charge is generated at the gripper or cup interface during separation, so the tooling and the ioniser, not the floor, control the part's charge.
Can standard vacuum cups be used in an ESD cell?
They can, but they generate and hold charge. Conductive or dissipative cups give the charge a path off the part at release and are the better default.
How do you verify the robot is actually grounded?
Check continuity from the cup or pad body to machine earth with the tool in its working position, including tool changers and cable carriers which break continuity.
Where should an ioniser be mounted in a robot cell?
Where the part actually rests before the next operation, and balanced and verified at that position. A bar that measures well at the outlet can be useless at the part.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.