Compressed air for robotics and end effectors

How robots use compressed air

An industrial robot is usually electrically driven, but much of what it does at the end of the arm is pneumatic. Typical air users in a robot cell are:

• Pneumatic grippers, parallel, angular or three-jaw, that close and open each pick.
• Vacuum cups and ejectors that pick cartons, sheets, panels and bags.
• Tool changers that lock and release tools with air and pass air circuits through to the tool.
• Compliance devices and balancers that use air pressure to set contact force.
• Process tools such as air-motor spindles, deburring tools, nutrunners and dispensing valves.
• Blow-off nozzles for cleaning parts, fixtures or welding torches.

Each of these behaves differently. Grippers consume a small fixed volume per stroke. Ejectors consume air the whole time they are switched on. Air-motor tools need sustained flow at a defined pressure. The air supply has to handle all of them, often within the same second of a cycle.

Why the air supply at the tool is different from the cell inlet

Between the plant connection and the gripper jaw the air passes through isolation, a filter-regulator, a valve manifold, the robot base connection, internal passages or an external dress pack, rotary joints, the wrist, a tool changer and finally short hoses to each actuator. Each element adds restriction and volume.

A gauge at the cell inlet can read 6 bar (87 psig) while the gripper sees much less during a fast close, because the hoses along the arm are long, small-bore and full of bends. When the robot moves, the hoses also flex, and kinked or worn sections add further loss. This is why grippers that work perfectly in a bench test can lose grip on the robot at full speed.

Good practice is to:

• mount the valves for gripper and vacuum functions as close to the tool as the dress pack allows, so the volume to fill each stroke is small;
• use the largest practical hose bore through the dress pack and keep runs short;
• check pressure at the tool, not only at the regulator, during motion at production speed;
• allow for the extra volume and restriction of rotary joints and tool-changer air passages.

Grippers: force, pressure and air consumption

Gripper force is proportional to the pressure behind the piston, so a pressure dip directly reduces the force holding the part. The robot’s acceleration adds inertial load on the part, often several times its weight during fast moves, and the gripper must hold that load with a safety factor at the lowest pressure the supply can deliver.

Air consumption per stroke is the internal swept volume of the gripper, plus the hose and valve dead volume, multiplied by the absolute pressure ratio. On small grippers the hose volume can be larger than the gripper itself, so long hoses from a manifold on the robot base can double the air per pick and slow the response.

Vacuum end effectors and ejector consumption

Vacuum ejectors use compressed air flowing through a venturi to create vacuum. They are light, simple and fast, which is why robot tools use them widely, but they consume compressed air continuously while switched on. A typical small ejector may use tens of litres per minute of free air; a large multi-cup tool for cartons or panels can use several hundred.

The biggest waste occurs when the ejector runs for the whole robot travel even though evacuation took a fraction of a second. Practical measures include:

• air-saving ejectors that switch off supply when vacuum reaches a set level and restart only if it decays;
• vacuum switches that confirm a secure pick before the robot moves;
• tight-sealing cups chosen for the surface, so leakage through porous or uneven material is not compensated by extra air;
• a separate electric vacuum pump where many cups run continuously, if the cell layout allows.

Ejectors are sensitive to supply pressure. Most are designed for a specific pressure, often around 4–6 bar (58–87 psig), and both too little and too much pressure reduce vacuum performance. Regulate them to their rated pressure rather than to the plant header.

Tool changers and multi-tool cells

An automatic tool changer usually locks pneumatically and passes several air circuits from the robot to the tool. Each tool change vents the air trapped in the outgoing tool’s circuits and fills the incoming tool’s circuits. In cells that change tools frequently, this venting and refilling becomes a noticeable part of the air demand.

Tool-changer locking is a safety-relevant function. Most designs include a fail-safe mechanism that keeps the tool locked if air is lost, but this must be confirmed for the actual model and the integrator’s design. Air supply changes, such as moving to a lower header pressure, should be checked against the changer maker’s minimum locking pressure.

Building the cell air demand profile

1. List every air function for each tool and configuration the robot program calls.
2. Map air events to robot states. Note when each gripper fires, when each ejector is on, when blow-off runs and when a tool change occurs.
3. Calculate free air for each event, including hose and valve volumes for actuators and on-time multiplied by rated consumption for ejectors and nozzles.
4. Find the peak, usually a gripper close or tool change while ejectors and blow-off are already running.
5. Add failed picks and recovery cycles. A repeat evacuation or re-pick uses air without producing a part.
6. Measure flow at the cell inlet and pressure at the tool over a full cycle at production speed.

The average flow sizes the contribution to the plant compressor. The peak sizes the local regulator, valve, hose and any small receiver at the cell.

Air quality and preparation for robot cells

Robot tools contain small valves, precision grippers and rotary joints that are easily damaged by moisture, oil degradation products and pipe scale. A refrigerated dryer giving a pressure dew point of about +3 °C, with general-purpose and coalescing filtration, is a typical minimum for cells in a dry indoor environment. Where air lines run through cold areas, outdoors or near chillers, or where air touches food or medicine, a desiccant dryer at about −40 °C PDP and finer filtration may be required.

At the cell itself, an FRL (filter, regulator and, only where the component maker requires it, lubricator) sets clean, stable pressure. Most modern grippers and valves are lubricated for life and should not receive added oil once they have run dry; starting and then stopping lubrication washes out the factory grease. A soft-start dump valve allows the cell to be pressurised gradually and vented safely.

Safe state on loss of air or power

The pneumatic design of a robot cell must state what happens to every air function if air pressure or electrical power is lost, or if an emergency stop is pressed. A gripper might hold its part using a spring or a pilot-operated check valve, or it might release. A vacuum tool loses vacuum within seconds unless it has a check valve and a reservoir. A tool changer should stay locked.

These decisions belong to the robot integrator and the machinery safety design, not to the compressed-air supplier. The supplier’s role is to make sure the air system provides the pressure and quality those safety functions assume, and that changes such as header pressure reduction are reviewed against them.

Common robot air problems

How Reddy Compressors helps

Reddy Compressors is an independent multi-brand compressed-air specialist based at Tarnaka, Secunderabad, serving industry since 2002. We sell new and used or refurbished compressors and dryers, rent machines from our own fleet, and provide service, AMC and spares for ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other brands, without being an authorised dealer of any.

For automotive, engineering, packaging and electronics plants using robots, we:

• log flow, pressure and dew point at the compressor house and at robot cells to separate supply problems from cell problems;
• recommend and supply compressors, dryers, filters and receivers to give stable, clean air at the cells;
• service and maintain the compressed-air plant so pressure and quality stay where the robot integrator’s design expects them;
• supply rental compressors during breakdowns or commissioning of new lines.

We do not design robot tooling or safety functions; we work alongside your integrator on the air supply side. Our engineers and technicians cover all of Telangana and Andhra Pradesh, and we supply across India.

What to send us

• Number of robot cells and the type of end effectors (grippers, vacuum, tool changers, air tools)
• Required pressure at the tools and any air-quality specification from the integrator
• The fault you see and when it happens (speed, shift, season)
• Compressor, dryer and filter details with nameplate photos
• A simple layout of the compressor house, main header and the cells

Frequently asked questions

What pressure do pneumatic robot grippers need?

Most industrial pneumatic grippers are designed for about 4–7 bar (58–101.5 psig), with force rated at a stated pressure, often 6 bar. What matters is the minimum pressure at the gripper during the fastest move, after losses in the dress pack and tool changer. Size the gripper so it holds the part, including acceleration loads, at that minimum pressure with a margin.

How much compressed air does a robot vacuum gripper use?

A vacuum ejector uses compressed air continuously while switched on. Small ejectors use tens of litres per minute of free air; large multi-cup tools for cartons or panels can use several hundred. Actual use depends on how long the ejector stays on each cycle, so air-saving ejectors that switch off once vacuum is reached can cut consumption considerably on long robot moves.

Why does my robot drop parts at high speed?

At high speed the part’s inertia adds load just as several air functions fire together. If pressure at the gripper dips because of long hoses, small bores, a restricting rotary joint or a weak supply, grip force falls below what the move needs. Log pressure at the tool during motion, check jaw and cup wear, and confirm the gripper’s force margin at the real minimum pressure.

Do robot grippers need lubricated air?

Usually not. Most modern grippers, valves and cylinders are lubricated for life at the factory and are designed for clean, dry, unlubricated air. Adding oil and then stopping washes out the original grease and shortens life. Use a lubricator only where the component maker specifically requires it, and focus instead on dry, well-filtered air at a stable regulated pressure.

What happens to a pneumatic gripper if air pressure is lost?

That depends on the gripper design and the circuit. Some grippers use internal springs or pilot-operated check valves to keep holding; others simply release. Vacuum tools lose their grip within seconds without check valves and a reservoir. The safe state is a machinery safety decision for the robot integrator, and the air supply must reliably provide the pressure their design assumes.

What air dryer is needed for a robot cell?

For indoor cells with ordinary grippers and valves, a refrigerated dryer giving a pressure dew point of about +3 °C with coalescing filtration is a typical minimum. Where lines pass through cold or outdoor areas, or air contacts food or medicines, a desiccant dryer at about −40 °C PDP and finer filtration may be needed. Confirm the dryer was sized for summer site temperatures.

Related pages

• Industrial vacuum pick and place systems
• Compressed air for packaging machines
• Directional valve flow and circuit response
• End-use air preparation and FRL selection
• Automotive manufacturing compressed air
• Pneumatic application engineering centre