When Is a Cobot Allowed to Run Without a Fence?

Never because of the machine, only because of the application. A collaborative arm may run without fixed guarding when a documented risk assessment shows every reachable contact stays inside the biomechanical limits, every pinch point is designed out or protected, and the result is verified by measurement rather than calculation. The vendor's word "collaborative" is not evidence, and roughly the same paperwork is required whether the arm weighs 18 kg or 800 kg.

The five conditions, in order

These are cumulative. Failing any one of them puts guarding back on the drawing.

1. The hazard is the arm, not the tool. A blade, a hot nozzle, a laser, a welding torch or an unsecured heavy part carries its own hazard that contact limits do not address. Those cells keep a fence regardless of what the arm is called.
2. Every reachable contact is classified. Each scenario is identified as transient or quasi-static and assigned a body region, because quasi-static limits are half the transient ones and clamping is the harsher case.
3. The head is unreachable. Contact with face, skull and forehead is not permissible under any circumstances. If a standing operator's head enters the swept volume, the layout has to change.
4. Pinch points are eliminated or protected. Gaps between the arm and a fixture, a table edge or a machine frame create clamping scenarios where a limb cannot retreat. Design them out, cover them, or restrict access.
5. The result is measured. Force and pressure at every reachable contact point, with a calibrated instrument and a spring element matched to the body region, capturing the peak in the first milliseconds.

What the file has to contain

Cases that keep guarding, every time

• Sharp or pointed tooling. The standard explicitly restricts collaborative parts with sharp edges such as knives or needles. Pressure limits assume a blunt contact surface.
• Thermal or radiation hazards. Welding, laser cutting, plasma, hot glue at 180 °C. Contact limits say nothing about burns.
• Heavy or unstable payloads. A part that can slip out of a gripper is a falling-object hazard independent of arm speed.
• Ejected material. Chips, coolant, offcuts and swarf come from the process, not the robot.
• High effective mass at speed. Above roughly 35 kg payload the permissible contact speeds fall so low that the cycle stops being viable, and separation-based operation becomes the honest answer.

The middle ground most cells actually land on

Very few real installations are fully unguarded. The common outcome is a partial arrangement that removes the fence where people work and keeps protection where the hazard is concentrated: a guard plate over the machine interface, a scanner that slows the arm on approach, a physical barrier behind the cell to stop back-side access, and contact-permitted operation only in the handover zone.

This is not a compromise, it is good design. It keeps the cycle fast in the segments nobody can reach and pays the collaborative penalty only in the 200 mm to 400 mm where a human hand actually meets the robot.

The legal frame in Europe

For machinery placed on the European market, Directive 2006/42/EC applies until 19 January 2027 and Regulation (EU) 2023/1230 applies from 20 January 2027, with no overlap period. The regulation entered into force on 19 July 2023 and gave a 42-month transition. Cells being designed now for delivery in 2027 should be assessed against the regulation, since the applicable rule is fixed by the date the machinery is placed on the market, not the date the project started.

Frequently asked questions

Sources