A pneumatic gripper may stop holding a part securely even without an obvious failure. The workpiece may start slipping, the fingers may close more slowly, the part position may become less repeatable, and during robot acceleration or rotation of the unit there may be a risk of displacement.
The cause is not always inside the gripper itself. The actual gripping force and holding reliability are affected by the air pressure at the device inlet, the quality of air preparation, the tightness of the pneumatic lines, the geometry of the working fingers, the condition of the part surface and the actual loads during the cycle.
It is important to distinguish between two cases:
- the force generated by the gripper decreases — this is usually related to pressure, leaks, contamination or wear;
- the ability to hold the part decreases — the cause may be not only the gripper itself, but also the fingers, oil on the surface, increased overhang, a shifted center of gravity or robot acceleration.
1. Insufficient Air Pressure at the Gripper Inlet
The force of a pneumatic gripper depends on air pressure and must be assessed within the operating range of the specific model. If the inlet pressure is lower than calculated, the jaws generate less force, and with friction-based holding the part may slip.
The problem often occurs not at the pressure regulator, but directly during the cycle. The pressure gauge before the line may show a normal value, but when several devices operate simultaneously, the pressure in the line may drop.
Pressure reduction may be caused by:
- insufficient capacity of the pneumatic network;
- an incorrectly selected pressure regulator;
- long or narrow hoses;
- restrictions in fittings, distributors and valves;
- simultaneous operation of several consumers;
- leaks in connections;
- contaminated filters.
Pressure must be checked dynamically, when the gripper opens and closes under operating load. It is necessary to compare not an arbitrary value in the line, but the actual pressure at the gripper inlet with the parameters specified in its technical documentation.
Do not increase the pressure above the permissible value stated in the model passport in an attempt to compensate for an incorrect selection. As pressure increases, the load on the fingers, guides and housing also increases. According to our recommendations, when the pressure is higher than nominal, the finger length must be proportionally reduced.
2. Moisture, Oil, Dust and Contaminated Compressed Air
A pneumatic gripper must not be connected directly to a compressor without air preparation. Moisture, oil residues, dust and other impurities enter the pneumatic channels, affect seals and moving parts, impair piston movement and may cause jamming.
Contaminated air leads to several typical problems:
- the gripper operates more slowly or unevenly;
- the fingers do not reach the end position;
- opening or closing force becomes unstable;
- jerks appear during jaw movement;
- wear of seals and guides accelerates;
- small holes and channels become clogged;
- in cold environments, condensate may cause the pipeline to freeze and the unit to operate abnormally.
In our technical manual, we directly state that air from the compressor must not be used without filtration: moisture and dust can cause corrosion, wear, jamming and blockage of small holes.
What to check:
- whether a filter is installed in the air preparation system;
- whether condensate is removed in a timely manner;
- whether the filter element is contaminated;
- whether the air quality meets the operating conditions;
- whether there is oil, moisture or emulsion in the pneumatic lines;
- whether additional purging or a dust-protected version is required for the specific model.
3. Working Fingers That Are Too Long or Too Heavy
The working fingers determine how the gripper interacts with the part. Even a correctly selected pneumatic gripper may lose efficiency if the fingers are too long, too heavy or have an unsuitable shape.
As finger overhang increases:
- the force at the contact point with the part decreases;
- the moment load on the jaws and guides increases;
- inertia during opening and closing increases;
- the risk of vibration and misalignment increases;
- the permissible load capacity of the gripping unit decreases;
- the service life of the equipment is reduced.
The fingers must be as short and lightweight as possible within the limits of the technological task. If the required length exceeds the permissible gripping distance, it is more rational to switch to a larger size or choose a series designed for higher moment loads.
For long fingers and demanding applications, it is worth considering VGFR parallel pneumatic grippers with a toothed guide. When selecting a model, it is also necessary to consider the permissible moments Mx, My, Mz and the lateral load Fz, not only the force specified in the table.
4. Leaks in the Pneumatic Line and Seal Wear
Air leaks are one of the most common causes of force loss and cycle slowdown. Even a small leak at a fitting, hose connection or distributor can become critical if the gripper operates at the lower limit of the working pressure range.
The following should be checked:
- threaded connections;
- fittings and quick-release couplings;
- hoses for bends, cracks and pinching;
- directional control valves;
- connections on mounting plates;
- piston seals;
- tightness of channels in the gripper and additional tooling.
Signs of leakage are not always obvious. Sometimes the gripper works normally without a part, but loses speed and holding capacity under load. Another typical symptom is different opening and closing times or unstable operation after several cycles.
As part of regular maintenance, we recommend monitoring air pressure, checking the condition of seals and keeping the guides clean.
5. Part Surface and Incorrect Holding Method
The maximum part weight specified in the pneumatic gripper card is not a universal guarantee of reliable holding. It depends on the gripping method and operating conditions.
With friction-based holding, the part is held by the friction force between the working fingers and the surface. If the surface is covered with oil, coolant, dust or has a low coefficient of friction, the actual holding capacity decreases.
Additional risks are created by:
- a smooth polished surface;
- oil and emulsion residues;
- metal chips in the contact area;
- unstable workpiece position;
- large overhang relative to the gripping point;
- a shifted center of gravity;
- high acceleration of the robot or gantry.
For such applications, it is often more reliable to use not only friction-based holding, but also form-fit holding: the fingers rest against a shoulder, groove, projection, hole or a specially provided contour of the part.
When selecting a gripper, it is important to determine in advance how exactly the workpiece will be held: only by friction or with the use of geometry. This choice affects the required force reserve, finger shape and gripper type.
6. Incorrect Gripper Size or Operating Conditions Outside the Permissible Range
A pneumatic gripper must match not only the weight of the part, but also the actual opening range, finger length, moments, cycle frequency and environmental conditions.
Errors occur when:
- the model is selected with a minimum force reserve;
- the diameter or width of the part is at the edge of the working range;
- the fingers exceed the permissible length;
- the operating temperature exceeds the parameters of the standard version;
- the gripper is installed in an area with high impact load;
- a basic version is used in a contaminated environment instead of a dust-protected version;
- the total weight of the gripper, fingers, part and adapter plate is not taken into account;
- the center of gravity is significantly offset from the robot wrist.
For round parts with end gripping, three-finger centering pneumatic grippers are usually considered, while four-finger models are used for square and special workpieces. For horizontal transfer of round bar stock, two-finger parallel grippers are more often suitable.
How to Quickly Identify the Cause of Force Loss
The inspection should be carried out step by step rather than replacing the gripper before diagnosing the entire system.
- Measure the pressure at the gripper inlet during the cycle.
Compare the value with the operating range of the specific model. - Check the lines for leaks and flow restrictions.
Inspect hoses, fittings, valves, connections and filters. - Assess the quality of compressed air.
Check for condensate, oil, dust and contaminants. - Inspect the fingers and the contact area with the part.
Check the shape, length, pad wear, contamination and fastening reliability. - Compare the actual conditions with the calculated ones.
The part weight, center of gravity, acceleration, finger overhang and holding method must correspond to the design solution. - Check the condition of the gripper.
Assess the smoothness of jaw movement, cleanliness of the guides, condition of seals and repeatability of end positions. - Check the position sensors.
They help identify a situation where the gripper has not fully opened or closed, although the command from the control system has already been sent.
How to Prevent Loss of Pneumatic Gripper Force
For a pneumatic gripper to operate reliably in an automated line, the basis must be correct engineering rather than minor adjustments:
- select a model with a reserve in force and moment load;
- design working fingers for the specific part;
- use a filter and monitor air preparation;
- regularly check system tightness;
- do not exceed the permissible pressure;
- consider the total mass of the gripping unit and the center of gravity;
- install position sensors for critical operations;
- select a dust-protected or heat-resistant version for difficult conditions;
- provide a safe scenario in case of pressure loss.
For applications where loss of air supply may lead to the part being dropped, versions with mechanical self-locking are available. The NC version maintains the closed position, while NO maintains the open position. However, self-locking does not eliminate the need to design the overall safety logic of the robotic cell.
When Engineering Support Is Required
Engineering selection is required if the part is heavy, has complex geometry, is covered with oil, is held by long fingers, moves with acceleration or must be accurately installed into a machine.
For selection, send a drawing or 3D model of the part, its weight, material, gripping zone dimensions, center of gravity position, required cycle time and operating conditions. KIPVALVE specialists will help select a pneumatic gripper, working fingers, position sensors and pneumatic system components for the actual production task.
Frequently Asked Questions
Can the force of a pneumatic gripper be increased by raising the pressure?
Only within the limits specified in the technical documentation for the specific model. Pressure above the permissible value may increase the load on the fingers, guides and housing rather than solve a selection error.
Why does the gripper hold the part manually, but the part falls out during robot operation?
When the robot moves, acceleration and inertial loads occur. If the center of gravity is offset, the fingers are too long or the surface is slippery, the holding force may be insufficient specifically under dynamic conditions.
Why has the gripper started working more slowly?
Common causes include pressure drop, filter contamination, leaks, a pinched hose, guide contamination, seal wear or flow restriction in the valve and fittings.
Are position sensors required for a pneumatic gripper?
For critical operations, yes. Sensors make it possible to check whether the jaws have reached the required position and help the control system stop the cycle before feeding the part into the machine or tooling.
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