Machine Design #07: Synchronizing Two Axes with Pneumatic Cylinders – Why You Should Be Careful

In FA (factory automation) machine design, there is a kind of mechanism that looks very simple at a glance but is, in reality, the cause of a great many mechanical faults:

Using two pneumatic cylinders to synchronize the motion of two axes.

Common examples are raising and lowering a large plate, pushing a long jig unit at both ends, clamping both sides of a workpiece at the same time, or moving a large mechanism with two cylinders mounted in parallel.

On the drawing, this approach looks quite reasonable.

Two cylinders of the same model. Two cylinders of the same stroke. The same solenoid valve. The same air pressure. Both mounted on the same plate.

So many people assume the two sides will move at almost the same time.

But in reality, a pneumatic cylinder is not a drive suited to accurate position synchronization. Just one side running a little faster and the other a little slower, and the mechanism can tilt, jam, twist; the guide rail can be pushed sideways; the cylinder rod can bend; or the workpiece can drop.

Especially for lift mechanisms, long-stroke mechanisms, large plates, or eccentric loads, using two independent pneumatic cylinders needs very careful consideration.

This article analyses why two pneumatic cylinders are hard to synchronize, the common design mistakes, and the practical measures to deal with them — meter-out, equal-length air piping, rack and pinion, link mechanisms, floating joints, external stoppers, and electric cylinders.

1. Why are two pneumatic cylinders hard to run in sync?

1.1. Air is compressible, so there is always a delay

The biggest reason a pneumatic cylinder is hard to synchronize is that its working medium is air.

Air is compressible. When the solenoid valve opens and air is supplied to the cylinder, the piston does not move immediately. The pressure inside the cylinder chamber has to rise to a level that overcomes the load, the seal friction, and the mechanism's resistance; only then does the piston start to move.

This is completely different from an electric drive such as a servo motor or a stepper motor.

With a servo, you can control position, speed, and acceleration by digital signals. But with a pneumatic cylinder, you are controlling a system that has elasticity, delay, friction, pressure variation, and many other mechanical errors.

When using two cylinders in parallel, even if both are fed from the same valve, just a small difference between the two air branches can make the start of motion diverge.

For example:

The air-tube length on the left and right is different.
The tube diameter or the fitting is different.
One side has more elbows.
One side has a heavier load.
One cylinder has greater seal friction.
One side's guide is stiffer.
The pressure rise in the two cylinder chambers is not the same.

The result is that one cylinder may have started to move while the other is still in the "pressure build-up" phase.

For small mechanisms, this deviation may not cause a big problem. But for a long plate or a mechanism with a large distance between the two axes, just a few millimetres of deviation can create a very large twisting moment.

So the first point to understand is:

You cannot expect two independent pneumatic cylinders to synchronize like two servo axes.

If the design requirement is "the two axes must be at the right position in real time", then using two independent pneumatic cylinders is a risky option.

1.2. Stick-slip shifts the moment of start-up

Another important cause is the stick-slip phenomenon.

Inside a pneumatic cylinder there are rubber seals that seal the piston and the rod. When the piston is stationary, the static friction is usually greater than the dynamic friction. Put simply, starting the piston moving needs a larger force than when the piston is already moving.

So when air is first supplied, the pressure in the cylinder rises gradually. When the pressure is large enough to overcome static friction, the piston starts to move. In many cases, it does not run smoothly right from the start but tends to "lurch" a little.

This is a very common phenomenon in pneumatics.

The problem is that the initial friction of the two cylinders is almost never exactly the same.

Even with the same model, the same maker, and the same stroke, there can be differences due to:

The condition of the grease inside the cylinder.
The wear of the seal.
Machining error.
Temperature conditions.
Assembly misalignment.
Side force acting on the rod.
Different actual loads on the two sides.

So one cylinder can start moving earlier than the other. When one side moves first, the plate or jig begins to tilt. If the guide mechanism is not rigid enough, this tilt keeps increasing the friction on the other side, making it run even slower.

The result is that a small initial deviation can be amplified into a large error.

This is why many machines can run acceptably when newly assembled, but after some period of use begin to jam, run jerkily, or drift out of alignment. As the seal wears, the guide gets dirty, the grease dries out, or the actual load changes, the already fragile synchronization is easily broken.

1.3. An uneven load makes one side run slower

On a 2D drawing, we often see a plate supported by two cylinders on both sides, and by default assume the load is split evenly. But in reality, the load is rarely split perfectly evenly.

If the center of gravity of the moving unit is shifted to the left, the left cylinder bears a larger load. If it is shifted to the front or rear, the guide may bear a larger moment. If the workpiece changes its placement, the load on the two sides also changes cycle by cycle.

When one side bears a larger load, the cylinder on that side needs a larger pressure to start moving. Its speed is also more prone to dropping when there is pressure fluctuation or increased friction.

Especially for a vertical lift mechanism, an uneven load is a very dangerous problem. If one cylinder lifts faster, the plate tilts. When the plate tilts, the load concentrates further on one side, making the mechanism even more prone to jamming.

For a two-axis design, you should not only ask:

Does the cylinder have enough lifting force?

You must also ask:

When the load is uneven and one side runs ahead of or behind the other, will the mechanism jam?

If the answer is "it might jam", that design is not yet safe.

2. Choose a lower load ratio when synchronization is needed

When choosing a cylinder for simple motion, there are many cases where you can choose with a relatively high load ratio. However, for a two-axis mechanism that needs to run in sync, you should choose more spare force.

The load ratio is the ratio between the actual load and the cylinder's theoretical thrust.

If the load ratio is too high, the cylinder is working almost at its limit. Then just a slight drop in air pressure, a slight increase in friction, or an uneven load will change the cylinder speed noticeably.

For a two-cylinder mechanism, this very easily makes the two sides diverge.

So when designing a two-axis pneumatic mechanism, choose a cylinder with relatively good spare force. In practice, a load ratio of about 0.3 to 0.5 is usually safer than choosing too tight.

Cylinder operating condition	Recommended load ratio	Design note
Ordinary horizontal / vertical motion	≤ 0.7	Usable for simple motion
Speed under 500 mm/s	0.3 – 0.5	Prioritize speed stability
Speed over 500 mm/s	0.2 – 0.3	Also consider impact and inertia
Two axes needing synchronization	0.3 – 0.5	Keep spare force to reduce the effect of uneven load

Reference: SMC Corporation https://www.smcworld.com/catalog/BEST-technical-data/pdf/AirCylinder-Select-Tech.pdf

The point to note is that a larger cylinder is not always better. If the cylinder is too large, the impact force at the end of the stroke also increases, the stopper mechanism has to bear a larger force, and the motion can be hard to keep smooth.

So the goal is not to choose a cylinder as large as possible, but to choose one that has enough spare force while still keeping speed, impact, and mechanical safety under control.

3. Stroke tolerance also shifts the final position

Even if the two cylinders run almost in sync during travel, there is still another problem at the end of the stroke: stroke tolerance.

A pneumatic cylinder is a mechanical part, so the actual stroke has a manufacturing tolerance. Two cylinders of the same model and the same nominal stroke can still stop at slightly different final positions.

For example, on the drawing both cylinders have a 300 mm stroke. But in reality, one may travel the full 300 mm while the other stops a little differently, within the allowed tolerance.

If the plate or jig is bolted rigidly to both cylinder rods, this error turns into a twisting force at the end of the stroke.

One side has reached the full stroke. The other still has a little to go. But because both sides are bolted rigidly to the same plate, the mechanism is forced.

The result can be:

The plate is twisted.
The guide is pushed sideways.
The cylinder rod bears an offset force.
The internal stopper of the cylinder takes uneven impact.
The machine runs for a while, then develops jamming or abnormal wear.

So for a mechanism that needs an accurate final position, you should not let each cylinder decide its own stopping point by its internal stopper.

A better way is to use an external stopper shared by the whole moving unit.

The external stopper creates a common mechanical reference surface. When the plate travels to the end of the stroke, the whole unit stops against this reference, rather than depending on the individual error of each cylinder.

Stroke range	Allowed tolerance	Note
≤ 250 mm	+1.0 / 0	Small and medium cylinders
251 – 1000 mm	+1.4 / 0	Large cylinders
1001 – 1500 mm	+1.8 / 0	Very large cylinders

Reference: TAIYO Ltd. https://www.taiyo-ltd.co.jp/products/pneumatic/docs/Catalog_7A2.pdf

A 1 mm error sounds small, but for a two-axis mechanism, especially when the distance between the two axes is large, it can create a significant moment.

In machine design, a small error at the part level can become a large fault when it enters the overall mechanism.

4. If you still use two pneumatic cylinders, what should you do?

It is not always necessary to absolutely forbid using two pneumatic cylinders. There are many cases where you can still use them, if the synchronization requirement is not too high and the mechanism is designed correctly.

However, understand that the measures below are to reduce risk, not to turn pneumatics into a servo.

4.1. Use meter-out for steadier motion

When controlling the speed of a pneumatic cylinder, there are two main ways: meter-in and meter-out.

Meter-in throttles the air supplied into the cylinder. Meter-out throttles the air exhausting from the cylinder.

In many ordinary pneumatic mechanisms, and especially in mechanisms that need to run steadily, meter-out is usually preferred.

The reason is that when you throttle the exhaust air, the chamber behind the piston still holds some pressure. The piston is not "shot" freely by the supply pressure but moves in a state with back pressure. This helps reduce jerking, reduce speed fluctuation, and make the motion easier to control.

For a two-cylinder mechanism, meter-out helps limit, to some extent, one side lurching out too fast. However, it does not fully eliminate the deviation between the two sides.

In other words:

Meter-out makes the mechanism easier to adjust, but it is not a solution for accurate synchronization.

If the design already has an uneven load, a weak guide, a long plate, and both sides bolted rigidly, adjusting the speed controller alone will not solve the root cause.

4.2. Make the air-tube length equal on both sides

The air piping also affects the response time.

If the left air tube is longer than the right, the volume of air to be filled in that branch is larger. The pressure may rise more slowly. In addition, the number of fittings, elbows, auxiliary valves, or throttles also changes the air-flow characteristics.

So when using two cylinders that need to run nearly in sync, try to make the two air branches as identical as possible:

Same tube length.
Same tube diameter.
Same type of fitting.
Same number of elbows if possible.
Same model of speed controller.
Place the valve close to the cylinder if you need to reduce the delay.

In practice, if one side must be placed closer to the valve, you can coil extra tube on the short side to balance the length with the long side. This is a simple method with a certain effectiveness.

However, it must be stressed again: equal piping only helps reduce the difference in response time. It does not deal with deviation caused by load, friction, stroke tolerance, or mechanism rigidity.

4.3. Do not expect adjusting the speed controller to be enough

A very common mistake is that when two cylinders run out of sync, the designer or the machine assembler only adjusts the speed controllers on the two sides.

At first it may be possible to adjust.

But then, after the machine runs for a while, it drifts out of sync again.

The reason is that the speed controller only adjusts the air flow under one specific condition. When the load changes, the air pressure changes, the seal wears, the temperature changes, or the guide gets dirty, that balance point changes.

So if the mechanism depends entirely on "adjusting the two speed controllers to be equal", that design is not stable in the long term.

A good design should not require the operator to keep fine-tuning so that the machine does not jam.

5. Locking synchronization mechanically: rack and pinion

If the two sides must be at the same position, a more reliable solution is to use a mechanical mechanism to lock the synchronization.

A common option is rack and pinion.

Both sides of the moving mechanism are fitted with a rack. The two racks mesh with a pinion or a common pinion shaft. When one side tends to move ahead, the gear mechanism forces the other side to follow. This way, the two sides are position-constrained mechanically.

The advantages of rack and pinion are:

Better position synchronization than adjusting air alone.
Less dependence on air pressure and the friction of each cylinder.
Easy to create parallel motion for a long plate.
Suits a mechanism that needs to keep the two sides from diverging much.

However, rack and pinion also has points to watch.

First is the torsional rigidity of the shaft. If the pinion shaft is too small or too long, then when the two sides have an offset force, the shaft can twist. Then the two sides still have a position deviation.

Second is backlash. A gear and a rack always have a certain meshing clearance. If the mechanism reverses direction or bears a reversing load, backlash can cause play and reduce accuracy.

Third is assembly accuracy. The two racks must be parallel, the meshing distance must be correct, and the pinion shaft must be straight and rigid enough. If misaligned, the mechanism can be heavy, wear quickly, or generate noise.

Fourth is the offset force between the two cylinders. If one cylinder pushes harder than the other, that difference in force is transmitted into the rack, pinion, and shaft. So you need to calculate the strength of the transmission, not just choose by feel.

In addition, if you use several gears on the same shaft, you need to watch the tooth position and the keyway position. Not every standard gear guarantees that the tooth position and the keyway are phased accurately.

According to reference information from KHK Kohara Gear, their standard gears have no product that comes by default with the tooth position and keyway accurately aligned. If alignment is needed, it must be custom-machined, and the accuracy is only at the level of aligning to a mark, not absolute accuracy.

This is a small but very important detail when designing a gear-based synchronization mechanism.

6. A better way: use one drive source and split the force with a link mechanism

In many cases, the best solution is not to use two cylinders and then try to synchronize them.

The better solution is to use a single cylinder, then split the motion to the two sides with a mechanical mechanism.

For example:

Parallel link.
Toggle link.
Rocker link.
A symmetric lever mechanism.
A common pivot shaft.
A cam or a two-sided pull-rod mechanism.

When there is only one drive source, the problem of "two cylinders running out of sync" almost disappears. The two sides are constrained by the same mechanism, so the motion is naturally more synchronized.

This is a very important way of thinking in machine design:

If you can use one drive source and split the force mechanically, do not rush to use several cylinders and then try to adjust with air.

This approach usually has many benefits:

Fewer cylinders.
Fewer valves.
Less air tubing.
Fewer points to adjust.
Easier maintenance.
Less dependence on air pressure.
More predictable mechanism behaviour.

Of course, the link mechanism also needs correct design. You need to check the stroke, the link angles, the forces at the joints, the play, the rigidity, the mechanical dead points, and the installation space.

But if done well, this is usually a cleaner and more stable option than using two independent cylinders.

7. The guide must be rigid enough; do not let the cylinder be the guide

A very dangerous design mistake is to let the cylinder both produce force and double as the guide.

A pneumatic cylinder is not designed to bear a large side force. The cylinder rod should mainly bear axial force. If a large side force or moment acts on the rod, the seal and the internal guide bush of the cylinder will fail quickly.

For a two-axis mechanism, when the two sides run out of sync, the plate tends to tilt. Without a rigid enough guide, this tilting force is transmitted into the cylinder rod.

The result can be:

The cylinder rod bends.
The seal wears quickly.
The cylinder leaks air.
The mechanism runs jerkily.
The plate jams.
The machine life drops sharply.

So in a correct design, the roles must be clearly separated:

The guide bears the guiding force and the moment. The cylinder only produces the push or pull force.

For lift mechanisms or long plates, use a linear guide, guide shaft, slide guide, or a dedicated guide mechanism with enough rigidity. Do not rely on the rigidity of the cylinder rod.

This is a very basic principle, but it is quite often overlooked in the design of small machines.

8. A floating joint helps avoid side force on the cylinder rod

When you attach the cylinder rod directly to a plate or jig, just a small deviation in the mounting center already pushes the cylinder rod off-axis.

This deviation can come from:

A mounting hole not at the exact absolute position.
A slightly tilted plate.
The guide and the cylinder not being perfectly parallel.
The two cylinders running slightly out of sync.
Different actual strokes on the two sides.
The mechanism deforming as the load changes.

A floating joint is used to absorb these small deviations.

It allows the cylinder rod end a certain degree of freedom, so the force transmitted into the cylinder is mainly axial. This reduces harmful side force on the rod and the seal.

For a two-cylinder mechanism, a floating joint is almost a part you should have, especially when:

The stroke is long.
The plate is large.
There is a dedicated linear guide.
There is a risk of eccentricity during assembly.
You need to reduce side load on the cylinder.
The two sides may not run perfectly in sync.

However, understand the role of the floating joint correctly.

A floating joint does not make the two cylinders more synchronized. It only keeps the cylinder from being destroyed by small deviations. In other words, it is a protective, eccentricity-absorbing part, not a synchronization mechanism.

9. You need a sensor and logic to detect axis deviation

In a two-axis mechanism, a dangerous situation is when one side has reached its position but the other has not yet arrived or has jammed.

If the system keeps supplying air, the mechanism can be twisted or destroyed.

So you should have a sensor to check the state of both sides.

For example:

An end-of-stroke sensor for the left cylinder.
An end-of-stroke sensor for the right cylinder.
A PLC that checks the arrival time of the two sides.
If one side turns ON but the other does not turn ON within the allowed time, stop the machine and raise an alarm.
If one side does not leave the initial position at the right time, raise an alarm.
If the previous cycle had an anomaly, do not allow the next cycle to run.

For a lift mechanism, you also need to consider the cases:

Air loss.
Power loss.
Emergency stop.
One cylinder leaking air.
One side mechanically jammed.
The work shifting position.
The pressure dropping while the plate is being lifted.

In these cases, if there is a risk of a dropped load, you need a drop-prevention mechanism or a separate mechanical lock. You should not rely on air pressure alone to hold the load.

Some line-sensor type sensors for cylinders can also be useful in a mechanism that needs to monitor the piston position more continuously than an ordinary ON/OFF sensor.

In addition, in the spirit of safe pneumatic-system design, you need to consider the foreseeable dangers and build them into the mechanical design, the air circuit, and the control logic. You should not only handle faults after the machine has already jammed.

10. An external stopper makes the final position more stable

As mentioned above, you should not let the final position of a two-axis mechanism depend entirely on the internal stopper of each cylinder.

The reason is that each cylinder has its own stroke tolerance. If the plate is bolted rigidly to the two cylinders, this error can force the plate to twist at the end of the stroke.

The external stopper is a very important solution.

Instead of letting each cylinder stop at its own stroke, you design an external mechanical stopper so the whole plate unit stops against the same reference surface.

An external stopper can be:

A stopper block.
A stopper bolt.
A urethane stopper.
A shock absorber.
A hard stop with a reference surface.
A stopper combined with a sensor to confirm the position.

When using an external stopper, watch for:

The stopper must be rigid enough.
The stopper position must be adjustable if needed.
The impact force at the end of the stroke must be calculated.
If the speed is high, use a shock absorber.
Do not let the impact force transmit badly into the guide or a thin plate.
The stoppers on both sides should be designed so they do not twist the mechanism.

An external stopper not only improves the accuracy of the final position but also makes the mechanism easier to adjust during actual assembly.

11. When should you switch to an electric cylinder?

If the mechanism requires accurate synchronization, stopping at multiple positions, changing position by recipe, soft speed control, or high repeatability, you should consider switching to an electric cylinder.

An electric cylinder uses a servo motor or a stepper motor to control the motion. So position, speed, and acceleration can be controlled by numerical parameters.

If you use a multi-axis controller, two axes can be synchronized far better than with pneumatics.

Advantages of the electric cylinder:

Position can be controlled.
Speed can be controlled.
Acceleration can be controlled.
It can stop at multiple positions.
It is easy to change by recipe.
There is position data for monitoring.
Less dependence on air pressure.
Reduced machine-adjustment time.
Suits mechanisms that require high stability.

The disadvantages are higher initial cost, the need for a power supply and a controller, and the need to watch the operating environment for dust, water, heat, or electrical noise.

However, you should not compare only the initial part cost.

With pneumatics, the initial cost may be low. But if the machine needs a lot of adjustment, drifts out of sync, jams, wastes maintenance time, consumes a lot of compressed air, or affects production, the actual total cost can be much higher.

Evaluation criterion	Pneumatic cylinder	Hydro-air cylinder	Electric cylinder
Synchronization accuracy	About ±2.0 mm, unstable	About ±0.5 – ±1.0 mm	Can be under ±0.01 mm
Drive rigidity	Low, because air is elastic	Medium	High
Environmental resistance	Good for heat, water, explosion-proof environments	Watch for oil leaks	Needs protection of electrical parts
Difficulty of adjustment	High, usually needs on-site tuning	Medium	Low, adjusted by parameters
Stopping at multiple positions	Not suitable	Limited	Suitable
Initial cost	Low	Medium	High
Long-term cost	Can rise due to adjustment and air leaks	Medium	Good if high stability is needed

Reference: IAI Corporation https://www.iai-robot.co.jp/download/catalog/pdf/RC-SOUGOU/CJ0159-4A-1/RC_2010-10_SHIRYOU(CJ0159-4A-1).pdf

If you only need simple motion between two points, a pneumatic cylinder is still a good solution.

But if you need accurate control, reliable synchronization, or a machine that runs production stably over a long time, an electric cylinder is an option to consider from the very start.

12. How to choose a design approach for a two-axis mechanism

When you meet a mechanism that needs to push, lift, or pull at two points, do not immediately place two cylinders on the two sides.

Think in the following order.

Step 1: Can you use one drive source?

If you can use one cylinder, one motor, or one main shaft and then split the force with a link, shaft, cam, or lever mechanism, this is usually a better direction.

One drive source eliminates the synchronization problem at the root.

Step 2: If you need two force-transmission points, can you lock them mechanically?

If you must transmit force on both sides, see whether you can use rack and pinion, a timing belt, a connecting shaft, or a parallel link.

If the two sides are locked mechanically, the stability is much higher than adjusting air alone.

Step 3: If you still use two independent cylinders, is deviation allowed?

If the two sides can deviate by a few millimetres and the mechanism is still safe, you can use two pneumatic cylinders.

But you need:

A rigid enough guide.
A floating joint.
An evenly distributed load.
Meter-out.
Balanced air piping.
Sensors to check the two sides.
An external stopper if an accurate final position is needed.
Logic to alarm when the two sides diverge in time.
A drop-prevention mechanism if it is a lift mechanism.

If these conditions are missing, the design very easily runs into faults in the field.

Step 4: If accuracy is needed, use an electric cylinder or servo

If the requirement is accurate synchronization, stopping at multiple positions, changing by recipe, or needing position data, switch to an electric drive.

Do not try to force a pneumatic cylinder to work like a servo.

13. Common design mistakes

Below are the mistakes that come up very often when designing a two-pneumatic-cylinder mechanism.

Mistake 1: Two cylinders bolted rigidly directly to one large plate

When the two cylinders do not run evenly, the plate twists. Without a floating joint or a rigid enough guide, the cylinder rods bear side force.

Mistake 2: Not accounting for the load's center of gravity

The cylinders are placed symmetrically on the drawing, but the actual load is off-center. One side bears a larger load, runs slower, and causes tilting.

Mistake 3: Not using an external stopper

Letting the two cylinders stop by their own strokes. The stroke error forces the plate at the end of the stroke.

Mistake 4: Adjusting only the speed controller to synchronize

At first it can be adjusted, but after conditions change, the two sides diverge again. This is an unstable fix.

Mistake 5: The cylinder doubling as the guide

No linear guide or guide shaft that is rigid enough. When there is a moment, all the side force goes into the cylinder rod.

Mistake 6: No deviation-detection logic

One side jams but the other keeps pushing. This is a fault that can destroy a mechanism very quickly.

Mistake 7: Choosing a cylinder with just enough force

Too high a load ratio makes the system sensitive to friction, pressure fluctuation, and uneven load. For two axes that need synchronization, keep reasonable spare force.

Conclusion: Synchronizing two pneumatic cylinders must be viewed from both pneumatics and mechanics

Using two pneumatic cylinders to synchronize two axes is an approach that can be used in some cases, but it should not be seen as the default solution.

Air is compressible, the cylinder has friction, the piping has delay, the actual load can be uneven, and the stroke of each cylinder also has a tolerance. All these factors make it very hard for two cylinders to run exactly alike.

If the mechanism only needs simple motion and allows small deviation, you can use two pneumatic cylinders. But you need a full design with a guide, a floating joint, meter-out, balanced piping, an external stopper, and sensors to check both sides.

If the two sides must be at the same position, use a mechanical synchronization lock such as rack and pinion, a connecting shaft, a timing belt, or a link mechanism.

If you need high accuracy, stopping at multiple positions, changing by recipe, or soft motion control, consider an electric cylinder or a servo actuator.

Key points to remember

On the causes of deviation

Air is compressible, so it is almost impossible to make two cylinders start exactly at the same moment like servo axes.
Differences in the friction of the seal and packing can cause stick-slip, making one cylinder start before the other.
The stroke tolerance of each cylinder can create a final-position deviation, even with the same model and the same nominal stroke.
An uneven load and an unbalanced workpiece center of gravity can make one cylinder bear a larger load and run slower.

On pneumatic design

For a mechanism needing synchronization, do not choose the load ratio too tight. Keep about 0.3 to 0.5 for spare force and to reduce the effect of an uneven load.
Meter-out throttles the exhaust air, creates back pressure, and makes the motion steadier, but it is not an absolute synchronization solution.
The air piping on both sides should be designed with the same length, the same diameter, and the same type of fitting, to reduce the difference in pressure-rise time.
Do not depend entirely on adjusting the speed controller to synchronize two cylinders, because the actual conditions will change over time.

On mechanical design

If reliable position synchronization is needed, use a mechanical constraint such as rack and pinion, a timing belt, a connecting shaft, or a link mechanism.
The ideal design in many cases is to use a single drive source, then split the force to the two sides with a mechanical mechanism.
The guide must be rigid enough to bear moment and side force; do not let the cylinder double as the guide.
A floating joint should be used to absorb assembly deviation and to avoid harmful side force on the cylinder rod.
An external stopper should be used to create a common stopping position, instead of letting each cylinder stop by its internal stopper.

On safety and actuator selection

You need a sensor and PLC logic to detect the case where one side reaches its position first and the other has not yet arrived or has jammed.
For a lift mechanism, also consider the risk of air loss, power loss, emergency stop, and a drop-prevention mechanism if there is a risk of a dropped load.
If the requirement is accuracy below the mm level, stopping at multiple positions, or synchronization by a motion profile, switch to an electric cylinder or servo actuator.
When comparing options, do not look only at the initial cost. Account for the adjustment time, the risk of a jammed mechanism, maintenance, air leaks, and production stability.

The most important point in design is not just:

Do these two cylinders have enough force?

You must ask deeper:

If the two sides run out of sync, is the mechanism still safe?

This is the right way to look at designing a two-axis mechanism in an FA automated machine.

A note from MINATA

MINATA shares these notes as reference material from a practical machine-design point of view. If you would like to discuss the choice of a two-axis drive, confirm drawings, compare options, or interpret Japanese–Vietnamese engineering terms during design, feel free to get in touch and we can review it together.

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