Collaborative Robots (Cobots): What They Are and How They Work
Collaborative robots — commonly called cobots — represent a distinct class of industrial robot engineered to operate in direct physical proximity to human workers without the fixed guarding that separates traditional industrial arms from the people around them. This page covers the formal definition and classification boundaries of cobots, the sensor and control mechanisms that make shared workspaces safe, the operational scenarios where cobots outperform alternatives, and the decision criteria that determine when a cobot is — or is not — the appropriate deployment choice. Understanding these factors is foundational context for navigating the broader regulatory and compliance landscape for robotic systems.
Definition and scope
ISO 10218-1 and ISO 10218-2, published by the International Organization for Standardization, establish the baseline safety requirements for industrial robots and their integration. Cobots fall within this framework but are further governed by ISO/TS 15066:2016, the first technical specification to address collaborative robot systems specifically. ISO/TS 15066 defines a collaborative robot operation as one where "a purposely designed robot system and a human operator work within the same workspace" — a definition that distinguishes cobots from conventional robots by the intentionality of shared space, not merely physical proximity.
The Association for Advancing Automation (A3), the primary North American robotics industry body, reports that cobot sales have grown substantially as a share of total robot orders, driven by lower integration costs and deployment flexibility in small and medium-sized facilities. Cobots are characterized by four properties that set them apart from caged industrial arms:
- Force and power limiting — hardware or software caps that restrict contact force, typically to thresholds defined in ISO/TS 15066's biomechanical injury limits
- Speed monitoring — real-time velocity control that reduces arm speed as humans enter defined proximity zones
- Safety-rated monitoring — sensor systems (torque sensors, joint encoders, proximity sensors) that meet Performance Level d (PLd) or Safety Integrity Level 2 (SIL 2) under IEC 62061
- Human-readable form factors — rounded joints, lightweight construction, and no pinch-point geometry that would cause crush injury at low force
The payload capacity of cobots typically ranges from 3 kg to 35 kg, distinguishing them from heavy industrial arms that carry 100 kg to 1,000 kg loads behind fixed barriers. The full spectrum of robotic system types — including traditional industrial arms, autonomous mobile robots, and service robots — provides the classification context within which cobots occupy a defined niche.
How it works
A cobot's ability to share space with humans depends on four collaborative operating modes defined in ISO/TS 15066:
Safety-rated monitored stop — the robot halts to a complete stop whenever a human enters the collaborative workspace, then resumes when the human withdraws. No physical contact occurs.
Hand guiding — a human physically moves the robot arm by gripping a handle equipped with a force/torque sensor, programming the arm's path by demonstration rather than code. The robot's control system reads applied forces and translates them into joint motion.
Speed and separation monitoring (SSM) — the robot continuously tracks the distance between its links and the human using laser scanners, camera systems, or radar. As the distance shrinks across defined thresholds, the robot reduces speed proportionally. At a minimum separation distance (MSD), calculated per ISO/TS 15066's formulas, the arm stops.
Power and force limiting (PFL) — the most widely deployed mode. The robot operates at reduced payload and speed so that any contact between arm and human stays below the biomechanical injury limits tabulated in ISO/TS 15066 Annex A, which specifies maximum permissible pressure (in N/cm²) and force (in N) for 29 distinct body regions.
The control architecture integrating these modes typically runs on a safety-rated programmable logic controller (PLC) or safety module certified to IEC 61508, the functional safety standard for electrical and electronic systems. Occupational Safety and Health Administration (OSHA) general duty clause obligations require that the overall risk assessment — conducted before deployment — document that all recognized hazards have been eliminated or controlled to acceptable levels (OSHA 29 CFR 1910.217 governs mechanical power presses as a proximate reference; cobot deployments rely on the general duty clause absent a cobot-specific OSHA standard).
Common scenarios
Cobots are deployed where the economics or ergonomics of full automation fail and traditional manual labor creates injury risk or quality inconsistency. The three most common deployment environments are:
Assembly and kitting — cobots handle repetitive pick-and-place, screw driving, or component insertion alongside human workers who manage exceptions, orientation corrections, and quality verification. The human provides judgment; the cobot provides precision and endurance.
Machine tending — a cobot loads and unloads CNC machines, injection molds, or presses. This task involves high repetition and awkward postures that generate musculoskeletal disorders. Because the cobot works at the machine interface rather than beside a moving human, PFL mode often suffices without additional guarding.
Quality inspection and measurement — a lightweight cobot arm positions a camera or measurement probe at precise coordinates across a part surface. Force limiting prevents probe damage on contact; hand-guiding mode allows technicians to teach new inspection paths in minutes rather than hours of offline programming.
Packaging and palletizing at lower throughput — where a full palletizing arm would be oversized and a human would perform 4,000 to 8,000 repetitive lifts per shift, a cobot operating in a shared zone manages consistent layers while humans manage pallet changeover and exception handling.
Decision boundaries
Not every collaborative task belongs to a cobot. Deployment decisions turn on six structural factors:
Cycle time requirements — cobots operating in PFL mode are limited to speeds typically below 250 mm/s when near human operators. If a task demands throughput that requires sustained high-speed motion, a caged industrial arm outperforms a cobot on unit economics.
Payload ceiling — a cobot rated at 16 kg cannot substitute for a 500 kg press-loading arm. Payload requirements above approximately 35 kg fall outside the cobot category as defined by current commercial and standards frameworks.
Risk assessment outcome — ISO/TS 15066 requires a formal risk assessment using ISO 12100 methodology before any collaborative operation is validated. If the assessment identifies hazards (sharp edges on parts, chemical exposure, high heat) that PFL mode cannot mitigate, additional guarding or a non-collaborative robot is required regardless of the cobot's sensor capabilities.
Workspace geometry — cobots excel in confined cells shared with workers. In wide-open floor environments where a human could approach from any vector, the sensor coverage required for SSM mode becomes complex and expensive, often eroding the cobot's cost advantage over a guarded alternative.
Contrast with autonomous mobile robots (AMRs) — cobots are fixed-base manipulators; autonomous mobile robots are mobile platforms that navigate floor environments. These categories are distinct and are sometimes combined (mobile manipulation platforms), but each carries its own standards obligations and risk profiles.
Regulatory classification — the robotic systems regulatory context in the United States does not include a single federal cobot standard. Compliance relies on the interplay of OSHA's general duty clause, ANSI/RIA R15.06 (the US adoption of ISO 10218), and ISO/TS 15066. Medical cobot applications additionally fall under FDA 21 CFR Part 820 quality system regulations if the cobot is part of a regulated device.
A summary of the robotic systems overview for this domain places cobots within the broader taxonomy of automation technologies and explains how adjacent system classes interact in integrated deployments.