A collaborative robot, often called a cobot, is a robot designed to operate in a shared workspace with people and to make physical contact safe through limited force, limited speed and built-in sensing. In robotics fundamentals, it marks a distinct category between the fenced industrial robot and the service robot that works among the public.
The defining feature is not the robot arm itself but how risk is controlled. A conventional industrial robot is made safe by keeping people away with guards and light curtains. A collaborative robot is made safe by designing the robot and the application so that contact stays below injury thresholds or is prevented by monitoring.
How a collaborative robot keeps contact safe
A collaborative robot combines mechanical design and safety-rated control to limit what happens when it touches a person. Typical arms are lightweight, with payloads from about 3 to 35 kg, rounded edges, no exposed pinch points and joints that can sense external torque.
Contact detection works in two main ways. Some designs place torque sensors in every joint, so the controller compares measured torque with the value predicted by the dynamic model and stops when the difference exceeds a threshold. Others estimate external force from motor current, which is cheaper but less sensitive. A safety controller, separate from the motion controller, runs these functions at performance level d or similar integrity so that a single fault does not disable them.
The international standards describe four ways in which a robot and a person can collaborate. The table below summarizes them as defined in ISO 10218 and the technical specification ISO/TS 15066.
| Mode | How safety is achieved | Typical application |
|---|---|---|
| Safety-rated monitored stop | Robot stops while a person is in the shared zone | Operator loads a fixture, then leaves |
| Hand guiding | Operator moves the robot with an enabling device | Teaching positions or assisted lifting |
| Speed and separation monitoring | Speed falls as the measured distance shrinks | Mobile workers near a palletizing cell |
| Power and force limiting | Contact forces kept below body-region limits | Side-by-side assembly at a workbench |
Key parameters of a collaborative robot
Choosing a cobot means balancing payload, reach and speed against the force limits the application must respect. Values vary between models, so the ranges below are typical rather than absolute.
| Parameter | Typical range | What it affects |
|---|---|---|
| Payload | 3 to 35 kg | Gripper plus part weight the arm can carry |
| Reach | 500 to 1,800 mm | Size of the reachable workspace |
| Repeatability | About 0.02 to 0.1 mm | Precision of returning to a taught point |
| Tool speed in collaboration | Often 250 mm/s or less | Contact energy and cycle time |
| Degrees of freedom | 6 or 7 axes | Dexterity and ability to avoid obstacles |
| Safety functions | Force, speed, zone and tool limits | Which collaboration modes are possible |
Speed during contact-capable motion is the parameter that most often surprises new users. Power and force limiting usually forces slower motion, because the permissible contact energy depends on moving mass and velocity. A cobot may therefore move at full speed when nobody is near and reduce speed when a scanner detects a person.
Collaborative robot compared with other robot types
The collaborative robot occupies a specific place among the main robot categories. The comparison below shows where it differs from its closest neighbors in robotics fundamentals.
| Category | Workspace | Safety approach | Typical strength |
|---|---|---|---|
| Collaborative robot | Shared with people | Force, speed and contact limits | Flexible tasks, quick redeployment |
| Industrial robot | Fenced or guarded cell | Separation from people | High speed and heavy payloads |
| Service robot | Public or domestic spaces | Low energy and navigation safety | Cleaning, delivery, assistance |
| Humanoid | Human environments | Still emerging for close contact | General-purpose manipulation research |
A common misconception is that a cobot is inherently safe. The standards treat collaboration as a property of the whole application, including the gripper, the part and the motion. A cobot carrying a sharp blade or a heavy casting can be as dangerous as any industrial arm, and an industrial robot fitted with speed and separation monitoring can collaborate safely.
Where collaborative robots fit in production
Collaborative robots pay off where tasks change often, floor space is scarce and volumes are moderate. Their graphical programming, hand-guided teaching and small footprint let a technician set up a new task in hours or days rather than weeks.
- Machine tending: loading CNC machines or injection molding presses.
- Screwdriving and assembly at benches where a person handles delicate steps.
- Quality inspection with a camera moved to repeatable viewpoints.
- End-of-line palletizing with area scanners and reduced-speed zones.
- Laboratory automation such as pipetting and sample handling.
The following decision table helps judge whether a cobot or a conventional industrial robot is the better fit.
| Situation | Better choice | Reason |
|---|---|---|
| Frequent product changeovers | Collaborative robot | Fast reprogramming and relocation |
| Cycle time under a few seconds | Industrial robot | Collaboration limits speed |
| Payload above about 35 kg | Industrial robot with guarding | Contact energy too high for collaboration |
| Worker and robot share the same part | Collaborative robot | Shared tasks need a shared workspace |
Limitations and common mistakes
The main limitation of a collaborative robot is throughput: the safety measures that allow contact also cap speed and payload. Planners who expect industrial cycle times from a cobot running in power and force limiting mode are usually disappointed.
- Skipping the risk assessment because the robot is marketed as collaborative.
- Ignoring the end effector, whose edges and clamping force often dominate the hazard.
- Validating forces only by calculation instead of measuring them with a force gauge.
- Placing the robot where it can pin a person against a wall, where clamping limits are much stricter than for free contact.
- Forgetting ergonomics and acceptance, which decide whether workers actually use the shared cell.
In everyday language
A collaborative robot is a robot arm built to work next to people rather than behind a fence. It is lighter, moves more gently and constantly feels whether it has bumped into something. If it touches a person, it stops or backs off before it can cause harm.
It is a little like a careful colleague at the next workstation: it handles the repetitive or tiring part of a job, while the person handles the steps that need judgment. The key point is that safety comes from the whole setup, not from the robot alone.
Seen in the real world
A small metal parts workshop runs two CNC lathes with one operator per shift. The company installs a 6-axis cobot with a 10 kg payload on a mobile stand between the machines. The robot takes raw blanks from a drawer, loads a lathe, removes the finished part and places it on a tray, while the operator measures parts and prepares the next job.
Because the operator walks through the shared area, the integrator runs a risk assessment, adds an area scanner that slows the robot to 250 mm/s when someone approaches, and measures contact forces at the gripper. After a short trial, the workshop runs the second lathe through lunch breaks and the late shift, and the operator spends more time on inspection instead of loading.