Industrial Robot Types and End Effectors

An industrial robot is a machine you can reprogram to move a tool or a part along a path, over and over. Robots now work in food plants, electronics, metalworking, plastics, packaging, and warehouses, not only on car lines. Each type has its joints arranged differently, and that arrangement decides what it can reach, how fast it can go, and where it can hurt someone. The tool on the end of the arm decides what the robot can actually do.

What You Will Be Able to Do

• Name the four main robot types and the kind of work each one suits.
• Explain why a collaborative application depends on much more than the arm.
• Read payload, reach, work envelope, and repeatability on a spec sheet without being misled.
• Match an end effector to a part, and ask what it does when air or power is lost.

Four Main Robot Types

Articulated Robots

An articulated robot has rotary joints in a chain from base to wrist, usually six of them. That gives it about the range of a human arm. It can reach around obstacles, come at a point from any angle, and hold a tool at a set angle while it moves.

That last ability is why a six-axis arm is the usual choice for arc welding. The torch has to follow a seam around corners and keep its angle the whole way. You will also see these arms spot welding, painting, palletizing, tending machine tools, dispensing adhesive, and deburring.

Payloads run from a few kilograms to more than 2,000 kg on models that lift whole car bodies. Reach runs from about 0.5 m to more than 4 m, and repeatability on most models is about +/- 0.02 to +/- 0.10 mm. The arm can swing above and behind itself, so it covers far more space than it seems to when parked.

SCARA Robots

SCARA stands for Selective Compliance Assembly Robot Arm. It usually has four axes: two rotary joints that swing the arm flat, one vertical axis that moves the tool up and down, and one that turns the tool.

The arm is stiff up and down but gives slightly from side to side, which helps it push a pin or screw into a hole. It is built for speed across a flat X-Y plane with a short vertical stroke, so it is strong at quick pick-and-place and small-part assembly, such as placing electronic components and driving screws. Typical figures are payloads of 1 to 20 kg, reach of 200 to 1,200 mm, and repeatability around +/- 0.01 to +/- 0.02 mm.

Delta Robots

A delta robot hangs over the work. Three or four thin arms run from a fixed base down to one small platform that holds the tool. The motors stay up in the base, so the moving parts are light and can change direction very quickly.

Delta robots often make more than 100 picks a minute, which suits lifting candy, baked goods, or packaged medicine off a moving conveyor. Payloads are small, usually about 0.5 to 8 kg. The reachable space is a shallow dome under the base, often 800 to 1,600 mm across.

Cartesian and Gantry Robots

A Cartesian robot moves along three straight axes, X, Y, and Z, on linear guides. A gantry robot is a Cartesian robot whose frame spans over the work. These can cover areas more than 10 m long and carry from about 2 kg to more than 500 kg, with repeatability around +/- 0.01 to +/- 0.05 mm.

You will see them moving parts between machines, palletizing large items, and guiding waterjet cutters, laser cutters, and 3D printers. They are easy to picture and program, but they cannot reach around things.

Collaborative Applications

People call some arms cobots, short for collaborative robots. The 2025 editions of the robot safety standards, ISO 10218-1 and ISO 10218-2, dropped that term in favor of "collaborative application". What makes a job collaborative is the whole setup: arm, tool, part, speed, and task, judged together by a risk assessment. The same arm may be fine to work beside with a soft gripper and unsafe with a sharp blade.

A well-designed collaborative application can let a person share the workspace without full safety fencing. The standards recognize three technologies for this:

• Hand guiding. A person moves the arm directly, using a hand control.
• Speed and separation monitoring. Sensors track how close a person is. The arm slows as they approach and stops before contact.
• Power and force limiting. The system keeps any contact under force and pressure limits set for each part of the body.

Arms sold for this work are smaller and slower than traditional robots. For light assembly, payloads of about 3 to 16 kg are typical, and larger models now carry 20 to 30 kg or more. Reach runs about 500 to 1,750 mm, and repeatability about +/- 0.03 to +/- 0.1 mm. There is no single collaborative speed. The allowed speed comes from the risk assessment for that job.

Warning: An arm sold as collaborative can still injure you. Treat it as any other machine until the risk assessment for that exact setup says you may work beside it.

Reading a Robot Spec Sheet

Payload

Payload is the weight the wrist can carry, and it counts everything mounted there, not only the part.

Say an arm is rated for 10 kg. The gripper weighs 3.8 kg, the adapter plate 0.4 kg, and the part 4.5 kg. The total is 3.8 + 0.4 + 4.5 = 8.7 kg, which looks fine.

Now check where that weight sits. As the center of gravity moves farther from the wrist, the allowed weight drops, and the maker's payload chart shows by how much. If the chart allows only 7 kg at this tool's offset, the setup is overloaded even though 8.7 is less than 10. An overloaded arm wears its gears faster and faults more often.

Reach and Work Envelope

Reach is how far the arm extends from its base at full stretch. The work envelope is the whole volume of space the end of the arm can get to. From the side it often looks like a thick curved shell, because the arm cannot reach every spot close to its own base.

Makers usually measure reach to the wrist. A long tool or part pushes the real reach farther out, so anyone planning a fence or floor marking has to count that extra length.

Repeatability

Repeatability is how closely the robot comes back to the same taught point, cycle after cycle. A rating of +/- 0.05 mm means the tool lands within 0.05 mm on either side of the point, a total spread of 0.10 mm. If a pin has 0.30 mm of total clearance in a hole, that spread uses 0.10 mm of it, and the rest has to cover the part, gripper, and fixture.

Repeatability is not accuracy, which is how close the robot gets to a position it has never visited. Think of darts: a tight group shows good repeatability, even if it is off to one side of the bullseye. Robots are usually much better at repeatability, which is why people teach them real points by moving them there.

End Effectors

The end effector is whatever is mounted on the robot's wrist. It is the part that touches the work. You will also hear it called end-of-arm tooling, or EOAT.

Grippers

Process Tools

Some end effectors work on the part instead of holding it:

• Arc welding torches and spot weld guns
• Spray guns for paint and coatings
• Dispensing nozzles for adhesive, sealant, or potting compound
• High-speed spindles for deburring and grinding

A tool changer lets a robot set down one tool and pick up another without help, so one arm can do several jobs in the same cycle.

Choosing an End Effector

1. Start with the part: material, shape, surface, weight, and how easily it marks.
2. Decide how to hold it: clamp its sides, seal on a flat face, or use a magnet.
3. Add up the total payload and check it against the payload chart.
4. Allow for variation. A cup that seals on clean sheet may leak on oily sheet.
5. Ask what happens if air or power is lost. A vacuum cup lets go. Some grippers hold on.
6. Look for new hazards: sharp edges, hot surfaces, sparks, and pinch points.

A new tool or part changes the risk, so it also means a fresh look at the risk assessment.

Common Mistakes

Check Your Understanding

1. A plant needs a robot to weld a curved seam on a bracket and keep the torch at the same angle all the way around. Which type fits?

A six-axis articulated arm. It can follow the curve and hold the tool angle at the same time. A SCARA or Cartesian robot cannot tilt the tool that way.

2. An arm is rated for 12 kg. The gripper weighs 5 kg, and the part weighs 6 kg and sticks out 300 mm past the wrist. Is it within its rating?

You cannot say yet. The total of 11 kg is under 12 kg, but the load sits far from the wrist. Check the payload chart for that distance.

3. A coworker says the arm with no fence is safe because it is a cobot. What would you ask?

Ask what the risk assessment for this tool, part, and task says. A sharp tool, a hot part, or a pinch point can cause injury even at low force.

Key Takeaways

• Joint layout sets what a robot can do: articulated for reach and angles, SCARA for fast flat work, delta for very fast light picks, Cartesian for long moves.
• "Collaborative" now describes the application, not the arm.
• Payload includes the tool, and the allowed weight falls as the load moves away from the wrist.
• The work envelope is the whole volume the arm can reach, and tools extend it.
• Repeatability of +/- X means a total spread of 2X, and it is not accuracy.