What Is a Collaborative Robot?
A collaborative robot, or cobot, is an industrial robot arm designed and controlled so that it can share a workspace with a human operator without a physical safety cage or fence separating them. This is a fundamental departure from how industrial robots have traditionally been deployed. The distinction is not marketing language — it is defined through specific engineering measures and a specific body of safety standards that dictate when a fence can legally and safely be removed.
A cobot achieves this through a combination of inherent design features and safety-rated control functions: rounded, padded, or pinch-point-minimized geometry on the arm itself; joint torque or force sensors that let the controller detect contact and react in milliseconds; and software-limited speed, force, momentum, and power ceilings enforced by a safety-rated monitoring system (not just the standard motion controller). None of this means a cobot is incapable of causing injury — it means the robot's contact energy has been engineered and validated to stay under defined injury thresholds for the specific application.
Cobots vs. Traditional Industrial Robots
A traditional industrial robot — the kind welding car bodies or moving heavy pallets — is typically fast, high-payload, and high-momentum. Its safety strategy is separation: perimeter fencing, interlocked gates, and light curtains keep people entirely out of the robot's work envelope whenever the robot is powered and capable of motion. If a person breaches that perimeter, the robot performs a safety-rated stop. The robot itself is not designed to limit the consequences of contact; the system around it is designed to prevent contact from happening at all.
A cobot flips that logic. Instead of relying purely on keeping the human out, it is engineered so that if contact does occur, the resulting force, pressure, or energy transfer stays below thresholds associated with injury. That allows the fence to come down (or be replaced by a much lighter safeguarding measure) — but it does not mean the robot is simply "safe" in every configuration. It means the robot and its application have been validated as safe for a specific, defined shared-workspace scenario.
The Standards That Actually Govern Cobot Safety
ISO 10218-1 and ISO 10218-2
ISO 10218-1 and ISO 10218-2 are the base safety standards for industrial robots generally, not cobots specifically. ISO 10218-1 covers the robot itself — the manufacturer's design requirements, including safety-rated monitored stop functions, speed limitation, and safety-related control system architecture. ISO 10218-2 covers the robot system as integrated into an application — the integrator's and end user's responsibilities for guarding, risk assessment, end-of-arm tooling, and the overall cell design. Both standards apply to every industrial robot, collaborative or not; they are the foundation.
ISO/TS 15066: The Collaborative Robot Specification
ISO/TS 15066 is a technical specification that sits on top of ISO 10218-1/-2 and applies specifically to collaborative applications. It is the document that actually defines what "collaborative" means in engineering terms, and it lays out four distinct collaborative operation types. A given cobot deployment may use one of these modes, or combine more than one within the same task cycle.
| Collaborative mode | Core mechanism |
|---|---|
| Safety-rated monitored stop | Robot halts completely when a person enters the shared space; resumes automatically once they leave |
| Hand-guiding | Robot moves only in direct response to an operator physically guiding the end effector, typically via a force sensor or dedicated handle |
| Speed and separation monitoring (SSM) | Robot dynamically slows or stops as a person approaches, based on real-time sensing (lidar, safety-rated vision, area scanners) and a calculated minimum protective distance |
| Power and force limiting (PFL) | Robot's own force, momentum, and power are inherently limited by design so any contact stays under injury-threshold biomechanical limits |
1. Safety-Rated Monitored Stop
This is the simplest collaborative mode: the robot is running at full industrial speed, but a safety-rated sensing system (light curtain, safety mat, area scanner) detects when a person enters the shared zone and commands the robot to a monitored stop. Motion resumes only after the person leaves and, in most implementations, after a deliberate restart signal. The robot itself does not need to be inherently force-limited in this mode, because it is never in motion while a person is present.
2. Hand-Guiding
In hand-guiding mode, the operator physically takes hold of the robot's end effector or a guiding device and leads it through the desired motion — this is how many cobots are taught points for a task, often called "teaching by demonstration." The robot's drive system responds only to the force applied by the operator; it does not execute pre-programmed autonomous motion while being hand-guided. A dedicated enabling device and force/torque sensing are required so the robot cannot move on its own during this mode.
3. Speed and Separation Monitoring (SSM)
SSM allows a person and a robot to occupy the same general area while the robot is actively performing autonomous work, by continuously tracking the distance between them. As the measured separation shrinks, the robot's speed is reduced proportionally, and if the person gets closer than a calculated protective separation distance, the robot stops. That protective distance is not arbitrary — ISO/TS 15066 provides a formula based on human and robot approach speeds, sensor and control system response times, and stopping distance, so the robot always has enough margin to stop before contact occurs. Lidar, safety-rated 3D vision, and area scanners are the typical sensing technologies used.
4. Power and Force Limiting (PFL)
This is the mode most people picture when they hear "cobot," and it is the one that allows genuinely simultaneous, close-proximity work without any separation distance at all. The robot's mechanical design (mass, joint compliance, rounded surfaces) and its control system (torque sensing at each joint, current-based force estimation) are engineered so that if contact with a person occurs — intentional or accidental — the transferred force and pressure stay below injury thresholds. ISO/TS 15066 provides biomechanical limit tables specifying maximum permissible force and pressure values for specific body regions (skull, face, neck, back, chest, abdomen, hands, and others), differentiated between quasi-static (clamping/trapped) contact and transient (free, glancing) contact. A PFL cobot application must be validated against these limits for its specific end effector, payload, and speed — not just against the robot's generic factory specification.
A Cobot Still Requires a Risk Assessment
Removing the cage does not remove the legal or engineering obligation to perform an application-specific risk assessment under ISO 10218-2 and the general machinery risk assessment standard ISO 12100. The robot arm may be power/force limited, but the end effector often is not — a gripper, a welding torch, a drill spindle, or a vacuum cup fixture can introduce crushing, cutting, or pinch hazards that have nothing to do with the robot's inherent force limits. The workpiece itself may have sharp edges or hot surfaces. A cobot carrying a sharp or heavy part can still exceed injury thresholds even if the bare robot, tested empty, would not. In practice this means every cobot cell still gets evaluated hazard by hazard, and additional safeguards (reduced speed near pinch points, guarding on the tool only, presence sensing) are frequently added even when the robot itself needs no fence.
Real-World Applications
- Machine tending — loading and unloading CNC machines, injection molding presses, and stamping presses, where an operator works nearby on other tasks
- Small-parts assembly — inserting fasteners, fitting components, or kitting parts alongside a human doing fine manual work
- Quality inspection — presenting parts to a vision system or handing parts to an inspector
- Packaging — case packing and carton erecting in tight production-line footprints
- Palletizing — stacking cartons or totes in space-constrained warehouse or production areas where a full robot cage isn't practical
Notable Cobot Manufacturers
Universal Robots, a Danish manufacturer, is widely credited with commercializing the modern cobot category with its UR3, UR5, UR10, and UR16 arms, named roughly for their payload in kilograms. Other established players include FANUC's CRX series, ABB's YuMi (a dual-arm cobot aimed at small-parts assembly) and GoFa series, and KUKA's LBR iiwa. This list is informational context on the category, not an endorsement of any single product — the right cobot for a given application depends on payload, reach, cycle time, and the specific collaborative mode the task actually requires.