Machine Design #20: Choosing an Electric Actuator for a Clean Room — From ISO Class and Dust Generation to Maintenance
When designing an automated machine for a clean room, many people immediately think of replacing the pneumatic cylinder with an electric actuator.
The reasoning is fairly easy to understand.
An electric actuator has no exhaust air like a pneumatic cylinder. It can control position, speed, acceleration and push force better. The motion is also smoother, with less impact if tuned correctly.
But that does not mean an electric actuator is automatically clean.
Inside an electric actuator there is still a linear guide, a ball screw, a belt, a bearing, grease, a motor cable, a sensor cable and possibly a cable carrier. All of these can generate particles if the wrong type is chosen, if they are installed wrongly, or if they are maintained incorrectly.
So when choosing an electric actuator for a clean room, do not just look at a few catalogue lines like "clean-room compatible" or "ISO Class 4." You need to understand clearly:
Under what conditions does the actuator reach that class? Does it need vacuum through a suction port? What grease is used? Is the seal structure tight enough? Do the cable and cable carrier generate dust? Can ordinary grease be used during maintenance? Does the factory have enough suction flow per the maker's requirement?
This article records how to choose an electric actuator for a clean room, from the ISO-class requirement, the dust-generation mechanisms, the dust-reduction technologies, and a maker comparison, to the points to watch during operation and maintenance.
1. A clean room must be understood by ISO class, not just a feeling of "clean"
Before choosing an actuator, you must confirm which cleanliness class the clean room requires.
The commonly used international standard is ISO 14644-1. It classifies a clean room based on the number of particles in 1 m³ of air by particle size.
The smaller the class, the cleaner the environment.
For example:
- ISO Class 3–5: common in some semiconductor, precision-electronics, optics processes.
- ISO Class 5–8: can be seen in pharmaceuticals, food, cosmetics, medical devices, assembly clean rooms.
- ISO Class 7–8: fairly common in many industrial applications needing dust control but not as extreme as front-end semiconductor.
An easy point to confuse is: the clean-room requirement must be considered in the operating state of the machine.
A stationary machine generates little dust. But when running, the guide moves, the ball screw turns, the cable flexes, the seal slides, the grease is agitated. It is exactly the operating state that reveals whether the actuator is really clean-room suitable or not.
2. A reference table of ISO 14644-1 and FED-STD-209E
Previously, many factories or old documents still used names like Class 100, Class 1000, Class 10000 under the old US standard FED-STD-209E.
That standard has been cancelled, but the naming is still used out of habit. So when reading an old spec or talking with a customer, understand the relative relationship between the two naming systems.
| ISO 14644-1 | Reference particle limit in 1 m³ of air | Old FED-STD-209E | Example application |
|---|
| ISO Class 1 | ≥0.1 µm: 10 | - | Very high-end semiconductor research |
| ISO Class 2 | ≥0.1 µm: 100 | - | Special ultra-clean environments |
| ISO Class 3 | ≥0.1 µm: 1,000 | Class 1 | Semiconductor, lithography, wafer process |
| ISO Class 4 | ≥0.1 µm: 10,000 | Class 10 | Etching, deposition, precision processes |
| ISO Class 5 | ≥0.1 µm: 100,000; ≥0.5 µm: 3,520 | Class 100 | Semiconductor back-end, cell culture, sterile pharma |
| ISO Class 6 | ≥0.5 µm: 35,200 | Class 1,000 | Electronic-component assembly, optics, sterile rooms |
| ISO Class 7 | ≥0.5 µm: 352,000 | Class 10,000 | Precision-equipment assembly, pharma, food |
| ISO Class 8 | ≥0.5 µm: 3,520,000 | Class 100,000 | Pharma, food, operating rooms, ordinary clean booth |
This table should be seen as a reference for technical discussion. When actually designing, you must check the customer's official spec and the standard applied in the project.
3. Where does an electric actuator generate dust?
An electric actuator has no exhaust air like a pneumatic cylinder, but it is still a mechanical mechanism with motion.
The main particle sources include:
3.1. Mechanical wear
Inside the actuator there is usually:
- A linear guide
- A ball screw
- A bearing
- A belt or pulley, depending on type
- A slider
- A seal sheet / seal band
- A sliding cover
When these parts move, the balls or rollers contact the rail, the ball screw turns in the nut, the bearing rotates, the seal slides on the cover surface. Even well lubricated and well designed, micro-wear can still occur.
For an ordinary machine, this level may be negligible. But in a clean room, even very small particles can matter.
3.2. Grease or oil flung off
The guide and ball screw need grease.
When the actuator runs fast, with large acceleration/deceleration or many repeated strokes, the grease can be agitated, flung off or slightly evaporate. Part of it can become a particle or outgas source.
So clean-room actuators usually do not use ordinary industrial grease, but low-particle grease / low-outgas grease.
3.3. Cable and cable carrier
This is a very easily underestimated dust source.
An electric actuator needs cables for the motor, encoder, sensor, brake, sometimes fieldbus or I/O. If the axis moves, the cable also has to flex back and forth.
If the cable is in a cable carrier, it can rub against the carrier or against itself. A worn cable jacket generates plastic particles.
A clean actuator paired with a cable carrier unsuitable for a clean room can still leave the system failing the requirement.
3.4. Mechanical impact and vibration
If the actuator stops too abruptly, hits the end stopper, or the payload vibrates strongly, the impact force can increase wear at the guide, ball screw, bearing and cover.
In a clean room, reducing shock is not only to protect the mechanics but also to reduce dust generation.
4. Three directions to reduce dust generation in a clean-room actuator
Makers usually combine the following three directions:
- Reduce generation at the source
- Keep particles inside
- Draw particles out with suction
In other words:
Generate less dust. If generated, do not let it escape. If there is still a risk of escape, draw it away.
5. Low-particle grease: not every grease can be used
Grease for a clean-room actuator differs from ordinary industrial grease.
Common requirements:
- Generates few particles
- Evaporates little
- Outgasses little
- Hard to fling off when running fast
- Compatible with the guide, ball screw, seal
- Does not degrade the actuator's clean performance
In practice you may encounter types such as:
- THK AFE-CA grease
- NSK LG2 / LGU grease
- Fluorine greases or clean-room greases specified by the maker
A very serious mistake is maintaining a clean-room actuator with ordinary grease.
The machine may still run, but the low-particle performance is almost destroyed. Ordinary grease can fling off, outgas or hold dust differently from grease designed for a clean room.
So the maintenance document must clearly state:
- Which grease to use
- The maker's grease part number
- How to apply
- The amount to apply
- The greasing cycle
- A ban on ordinary grease unless allowed by the maker
This is not a small matter. For a clean room, applying the wrong grease can turn a clean actuator into a contamination source.
6. Seal sheet, seal band and full-cover structure
A very common technology in clean-room actuators is using a seal sheet / seal band to cover the slider gap.
Because the actuator slider has to move, the actuator body always has an open region for the slider to pass through. Without good covering, particles generated inside can escape through this gap.
The seal sheet is usually a thin sheet, possibly stainless or a suitable material, running along the actuator body to cover the open region.
This structure serves to:
- Limit internal particles escaping outward
- Limit external dust entering the actuator
- Keep grease and wear dust in a controlled region
- Increase clean-room usability
However, a seal is also a friction surface. If poorly designed, wrongly installed, or damaged, it can become a dust source.
When choosing an actuator, look at:
- Is there a seal sheet / seal band?
- What material is the seal?
- Is there a full-cover structure?
- Does the slider tear or pull the seal off-line?
- Is periodic seal inspection required?
- Is the cover area easy to clean?
7. Suction port: reaching a high class usually requires suction
For a high clean-room class, many actuators do not rely on the seal alone.
They need a suction port / vacuum port.
The suction port is a suction connection on the actuator body. When connected to the factory's suction system, the air inside the actuator is drawn out continuously. Thanks to this, the inside of the actuator tends toward a slight negative pressure, and particles have difficulty escaping through the gap.
This is a very important point when reading a catalogue.
There are products stating they reach ISO Class 3 or ISO Class 4, but the attached condition is:
Suction through the suction port at a certain flow rate is required.
That is, the actuator does not naturally reach that class in all conditions. It reaches it when installed correctly, drawn correctly, with enough suction flow and the test environment matching the maker's stated conditions.
When choosing a type with a suction port, check:
- Is suction required, or optional?
- What suction flow rate is required?
- Is the unit L/min or NL/min?
- What negative pressure is required?
- Suction at one point or several?
- Does the factory have an adequate exhaust/vacuum system?
- If several actuators draw together, is the total flow enough?
- Is there a filter or trap on the suction line?
- If suction is lost, does the actuator still reach the clean class?
If you do not account for suction from the start, machine installation later very easily produces faults: not enough vacuum ports, suction tubing too small, piping too long, actual flow insufficient, or no point to connect to the exhaust system.
8. Do not just choose the actuator — choose the installation conditions too
For a clean-room actuator, the catalogue usually gives test conditions.
For example:
- Mounting orientation
- Speed
- Acceleration
- Load
- Stroke
- Suction flow rate
- Grease
- Measured class
- Measured particle size
- Trial-run duration
If the real application runs faster, with a heavier load, higher acceleration, or without the correct suction flow, the real result can differ.
So when choosing an actuator, compare the catalogue conditions with the real machine conditions:
- Real speed
- Acceleration / deceleration
- Payload
- Duty cycle
- Stroke
- Moment load on the slider
- Mounting orientation: horizontal, vertical, inverted, tilted
- Temperature
- Actuator position relative to the workpiece
- Whether there is a cable carrier
- Whether there is a suction line
- Whether there is maintenance access
A clean-room actuator should not be chosen by part number and then installed. It must be chosen as a whole system.
9. A comparison table of clean-room actuator makers
The table below is an overview to orient the initial choice. When choosing a real model, you must still check the latest catalogue, the test conditions and the project's clean-class requirement.
| Maker | Representative series | Actuator type | Representative ISO class | Dust-reduction technology |
|---|
| IAI | EleCylinder clean spec, RCP6CR, RCS4CR, ISDBCR | Slider, rod, rotary, SCARA | Class 2.5 / 3 by model | Stainless sheet, internal suction, roller structure, low-particle grease |
| THK | Clean series CSKR, CGL, CKSF, CKRF | Slider | Class 4, usually needs suction | Dedicated seal sheet, full cover, suction port, AFE-CA grease |
| SMC | Clean series LEFS, LEJS | Slider, rod | Class 4 by model | Seal band, suction port, low-particle grease |
| Oriental Motor | EZS clean-room model | Slider | Class 3, usually needs suction | Roller structure, stainless sheet, suction port, low-particle grease, stated suction flow |
| NSK | Monocarrier clean type, low-particle/decontamination actuator | Slider | Class 4 / 5 by line | Seal belt, NSK K1, LG2/LGU grease |
| CKD | EJSG low-particle environment type | Slider | Class 3 by model | Full cover, suction port, low-particle grease |
| Yamaha Motor | Clean-room robot: single-axis, Cartesian, SCARA | Robot / single-axis / Cartesian / SCARA | By model | Sealed structure, improved suction efficiency, robot-system design |
Note: the "representative ISO class" does not mean every model of that maker reaches that class. You must read the exact model, the exact option and the exact suction condition.
10. IAI: wide line-up, high class, many choices for clean automation
IAI is a very strong maker of electric actuators and small robots for automation.
For clean rooms, IAI has many lines such as:
- EleCylinder clean specification
- RCP6CR
- RCS4CR
- ISDBCR
- Slider type
- Rod type
- Rotary type
- SCARA clean specification by line
IAI's strength is a wide line-up and models reaching very high cleanliness, possibly down to the ISO Class 2.5 / 3 region depending on product and conditions.
Common technologies:
- Sealed stainless sheet
- Internal suction
- Roller structure to reduce friction and dust generation
- Low-particle grease
- Many different mechanism forms
IAI suits when you need:
- Many choices of stroke, load, speed
- To replace a pneumatic cylinder with an electric cylinder
- To design semiconductor or precision-electronics machines
- A high clean-room class
- To synchronise multiple actuator axes
However, when choosing IAI you must also check the class-achieving conditions carefully, especially the suction requirement, mounting orientation and running conditions.
11. THK: strong in the guide, cover and grease foundation
THK is a maker strong in linear motion, especially the LM guide.
THK's clean actuators are usually in clean series such as:
Some lines aim for a better low-particle structure, some are a simple clean structure to balance cost and performance.
Notable points:
- Full-cover structure
- Dedicated seal sheet
- Suction port
- Low-particle grease AFE-CA
- A reliable guide/ball-screw foundation
With THK, note that many products reach the stated clean class under a condition of suction through the suction port. So you must account for the suction system from the layout stage.
THK suits when:
- You need a stable slider mechanism
- You prioritise the reliability of the guide and ball screw
- You want to choose by clear technical documentation
- You need to balance cleanliness, rigidity and life
12. SMC: easy to pair with existing pneumatic and automation systems
SMC is famous for pneumatics, but SMC's electric actuators also have many lines used in automated machines.
Clean-room lines you may encounter:
- LEFS clean series
- LEJS clean series
- Slider type
- Rod type depending on configuration
Common technologies:
- Seal band
- Suction port
- Low-particle grease
- Structure to reduce grease scattering and limit foreign matter
SMC has an advantage if the machine already uses many SMC devices:
- Pneumatic system
- Valve
- Sensor
- Speed controller
- Vacuum component
- SMC controller/driver
Standardising on one maker can make purchasing, spare-part management and support easier.
But do not skip the clean-class condition just because you are used to SMC. For each model you still have to check the catalogue and the suction condition.
13. Oriental Motor: strong in motor, controller and quantified suction data
Oriental Motor has actuators such as the EZS series clean-room compatible.
A notable point is that some models clearly state the suction condition, for example a suction flow requirement at a specific level such as around 20 L/min or more depending on the model.
For the designer, such quantified information is very valuable, because it lets you check:
- Does the factory have an adequate suction system?
- What diameter to choose for the suction tubing?
- If there are several actuators, what is the total suction flow?
- Is a dedicated suction manifold needed?
- If suction is insufficient, how much does clean performance drop?
Oriental Motor suits when:
- You want an actuator tightly integrated with a clear motor/controller
- You need to choose by quantified data
- You need a high clean class such as ISO Class 3 by model
- You prioritise ease-of-use in motor control
14. NSK: strong in ball screw, monocarrier and lubrication technology
NSK has a very strong foundation in bearings, ball screws and linear motion.
The Monocarrier clean type integrates a ball screw and a linear guide into one compact unit.
NSK's strengths lie in:
- High-quality ball screw and guide
- Seal belt / cover
- Low-particle grease LG2 / LGU
- The NSK K1 lubrication unit
- Aiming for long life and reduced maintenance
NSK K1 is a notable point. It is a lubrication technology using an oil-impregnated polymer material, helping maintain lubrication for a long time and reducing maintenance needs in some applications.
In addition, NSK also has a development direction of low-particle and decontamination-compatible actuators for fields such as regenerative medicine or aseptic manufacturing, where it may need to withstand a decontamination process such as hydrogen peroxide.
NSK suits when:
- You need high mechanical reliability
- You want a compact ball-screw + guide unit
- You prioritise long-life lubrication
- You have a limited-maintenance requirement
- Medical, pharma, aseptic applications need special consideration
15. CKD: clean actuators and strength from automation equipment
CKD has pneumatics, fluid control and electric actuators.
For clean-room actuators, you may encounter the EJSG low-particle environment type.
Common features:
- Full-cover structure
- Suction port
- Low-particle grease
- Some lines aiming for ISO Class 3 by model
- Flexibility in combining motors from various makers
CKD also has an advantage because the same ecosystem has many clean pneumatic components, filters, valves and related devices.
CKD suits when:
- The machine uses many CKD devices
- You need to combine pneumatic clean components and an electric actuator
- You need a low-particle solution with full cover and suction
- You want flexibility in choosing the motor
16. Yamaha Motor: choosing along a robot-system direction
Yamaha Motor is strong in industrial robots: single-axis robots, Cartesian robots, SCARA robots.
For clean rooms, Yamaha does not just sell a single actuator but usually aims at a robot system:
- Single-axis clean robot
- Cartesian clean robot
- SCARA clean robot
- Clean-type lines by model
The strength is the overall design for the robot:
- Sealed structure
- Improved suction efficiency
- Optimised to the robot motion
- Able to deploy a whole axis system rather than individual actuators
Yamaha suits when:
- You need a pick-and-place robot in a clean room
- You need a SCARA clean type
- You need a multi-axis synchronised Cartesian system
- You want to choose by system rather than assembling each axis yourself
If the mechanism is just a simple single axis, single-axis actuator makers may be easier to choose. But if the problem is a whole robot in a clean room, Yamaha is a choice worth looking at.
17. Cable carrier: a very easily forgotten dust source
One real mistake is choosing a clean-room actuator very carefully, but choosing an ordinary cable carrier.
A cable carrier runs back and forth continuously. Inside there are motor, encoder, sensor cables, sometimes an air tube or vacuum tube. If poorly designed, the cables rub against each other or against the carrier.
The result is the cable jacket and carrier plastic being abraded, creating particles.
For a clean room, consider:
- A low-particle-type cable carrier
- Clean-room-compatible cable
- A separator to separate the cables
- The correct bend radius per the cable
- Not stuffing too many cables into the carrier
- Not letting the cables twist or cross
- Not letting the tube/cable rub against sharp edges
- Checking accumulated dust after a trial run
Some clean-type cable carriers can aim for ISO Class 1 or 2 depending on line and conditions. But you still have to choose the right size, the right material and the right layout.
Do not let a cheap cable carrier ruin the whole clean design.
18. Maintenance: absolutely do not use ordinary grease
A clean-room actuator only keeps its performance if maintained correctly.
The most dangerous point is grease.
If maintained with ordinary industrial grease, the actuator can lose its low-particle capability. Worse, once ordinary grease has entered the guide, ball screw and seal, it is very hard to restore to the original state.
The basic maintenance procedure should have:
- Cut the machine power and ensure safety.
- Check the maker's documentation to confirm the grease type.
- Use a suitable clean wipe to wipe off the old grease.
- Do not let cloth lint, fibres or foreign matter fall into the actuator.
- Apply the correct new grease, in the right amount, a thin even layer.
- Move the slider by hand a few times to distribute the grease evenly.
- Wipe off excess grease if any.
- Check the seal sheet, suction tube, cable carrier.
- Trial-run at low speed before returning to the real cycle.
A common maintenance benchmark can be:
Around 100 km of running or 3–6 months
However, this is only a reference benchmark. The real cycle must follow the catalogue, duty cycle, load, speed, environment and factory requirement.
If the actuator runs at high speed, high duty or a strict clean class, the inspection cycle may need to be shorter.
19. Checklist for choosing an electric actuator for a clean room
Before finalising the design, check the following points.
19.1. Clean-room requirement
- What is the required ISO Class?
- Measured by which particle size?
- Required when the machine runs or when stationary?
- Is there an ESD requirement?
- Is there an outgas or special-material requirement?
- Is there a decontamination process or cleaning chemical?
19.2. Actuator
- Is the actuator the correct clean-room type?
- What is the stated class?
- Does that class need suction?
- Are the speed, acceleration, payload, moment within the stated conditions?
- Is the mounting orientation suitable?
- Is there a seal sheet / seal band?
- Is there a full-cover structure?
- What low-particle grease is used?
- Are spare parts and maintenance documentation available?
19.3. Suction / exhaust
- Is there a suction port?
- What suction flow is required?
- Does the factory have enough flow?
- If several actuators draw together, is the total flow calculated?
- Is the suction tubing too long or too small?
- Is loss of suction monitored?
- Is there a filter/trap on the suction line if needed?
19.4. Cable and cable carrier
- Is the cable clean-room compatible?
- Is the cable carrier a low-particle type?
- Is a separator used to avoid cables rubbing?
- Is the bend radius correct?
- Are the cables pulled, twisted or rubbing on the cover?
- Is dust generated in the carrier after a trial run?
19.5. Maintenance
- Which grease is specified?
- Is ordinary grease banned in the maintenance instructions?
- Is the lubrication cycle by km or by time?
- Is there space to grease, clean, replace the seal?
- Are the suction tube and cable carrier easy to check?
- Is there a correct clean-wipe procedure?
19.6. Overall layout
- Is the actuator above the product?
- If particles escape, do they fall onto the work?
- Is the downflow used?
- Is local exhaust needed?
- Is there any easily-rusting or peeling-coating material?
- Do cable/tube pass over the product area?
20. Conclusion
An electric actuator is a very strong choice for a clean room, especially when you need control of position, speed, acceleration and reduced impact.
But an electric actuator is not automatically clean just because it has no exhaust air.
The dust source can still come from the guide, ball screw, grease, seal, cable and cable carrier. For a high clean class, the suction port and the real suction flow are no less important than the actuator itself.
When choosing an electric actuator for a clean room, look at it as a system:
- Which class does the clean room require?
- Under what conditions does the actuator reach that class?
- Is suction needed?
- Are the grease and seal the correct clean type?
- Does the cable carrier generate dust?
- Does maintenance use the correct grease?
- Does the layout prevent particles falling onto the product?
In short:
A clean actuator is not just a part number in a catalogue. It is a combination of actuator, grease, seal, suction, cable, layout and maintenance.
Choosing right from the start makes the machine cleaner, more stable and less in need of fixing after it goes into the clean room.
View all MINATA technical articles