How to use an ionizer and design an automatic machine! Thorough explanation of the types and selection of installation locations.

In this section, we will discuss the use ofanti-static (elec)　It may be incorporated into an automatic machine inIonizer."The following is a note on the basics of

When you start looking into ionizers, you will find a myriad of types and technical terms, and you will be at a loss as to which one is the right choice and how to incorporate it into your design to avoid problems.　In this article, we will introduce the Ionizers from an "engineering viewpoint" based on the challenges designers face in the field, which cannot be read only from the introduction of product features on a general manufacturer's website.Practical knowledge to keep in mind　The following is a summary.

By understanding the physical mechanism that generates static electricity, you will be able to determine the design flow from ionizer selection to placement without hesitation. Furthermore, this article provides a comprehensive explanation of maintenance design to achieve stable operation over a long period of time.　　By reading this article, you will (should) be able to systematically organize your fragmented knowledge, confidently select the optimal ionizer, and design trouble-free automatic machines.

Basics and principles of using the ionizer

Charging Mechanisms and Electrostatic Disruption (ESD)

When designing an automatic machine, the first thing to understand is the physical background of why static electricity is generated in the process.　　Charging phenomena at manufacturing sites are mainly classified into three categories: exfoliation charging, in which electric charges are transferred when materials come into contact or are separated; friction charging, in which objects rub against each other; and induction charging, in which electric charges are generated on conductors when charged objects approach.

For example, a strong peeling charge is generated during the process of pulling a component tape from a reel, and a workpiece moving in a vibrating bowl is exposed to a severe frictional charge.　　These phenomena cause a buildup of static electricity on the surface of the workpiece.　　When this accumulated voltage touches a grounded metal nozzle or electronic components such as IC chips, electrostatic destruction (ESD) is triggered, which causes an instantaneous electric current to flow.

In recent years, electronic devices have become increasingly miniaturized, and more and more cases of dielectric breakdown occur even at potentials as low as several tens of volts.Machine designers need to clarify the risk level of each process (whether they want to prevent electrostatic breakdown or foreign matter adhesion) and select specifications accordingly, rather than simply making room for an ionizer.　It is also important to understand that static electricity is a major cause of contamination in clean environments because it attracts airborne particles through Coulomb force.

Table 1: Major Failures Caused by Static Electricity and Points to Consider When Designing

Reference source: Keyence anti-static textbook (https://www.keyence.co.jp/ss/products/static/static-electricity/step/ionizer.jsp）

Reference source: SMC Ionizer Equipment Selection Guide (https://www.smcworld.com/catalog/New-products/mpv/s100-97-izs40/data/s100-97-izs40.pdf）

Ion generation by corona discharge

Most industrial ionizers use a phenomenon called "corona discharge," in which air molecules are electrically decomposed to produce ions.　　Understanding how this works is very helpful in preparing for a proper installation environment.　　The discharge needle (emitter) of an ionizer is subjected to high voltages of several thousand volts.　　The tip of the needle is very sharply shaped, and the concentration of the electric field here causes localized dielectric breakdown, ionizing the surrounding air into positive and negative ions.

The generated ions are attracted to the charged workpiece by Coulomb forces.　　If the workpiece is positively charged, negative ions will selectively bind to it, and if it is negatively charged, positive ions will selectively bind to it, returning it to an electrically neutral state.This is called "neutralization.

It is important to note that positive and negative ions have different physical properties.　　In general, negative ions have a smaller mass and move more easily, so discharging them under the same conditions tends to result in an excess of negative ions.　　In addition, a small amount of ozone is generated by corona discharge, which may accelerate the deterioration of rubber parts (e.g., O-rings).Designers should consider ozone-resistant fluoroelastomers and silicone rubbers when selecting materials for the area around the ionizer.is also required.

Ion balance and ionization speed

When looking at the ionizer performance chart, "ion balance (offset voltage)" and "ionization speed (decay time)" are always listed.　　Since these are often trade-offs, priorities must be determined according to the specifications of the automated machine.

The static elimination speed refers to the time required to reduce a charged potential (e.g., 1000 V) to a specific level (e.g., 100 V).In high-speed transfer lines with short takt time, the workpiece passes in front of the ionizer in an instant, requiring extremely high ionizing speed.　　Ion balance, on the other hand, indicates the equilibrium state of the amount of positive and negative ions supplied.　　The closer this value is to 0 V, the more ideal it is. However, if the balance is out of balance, voltage may remain on the workpiece after static elimination, or the workpiece may be charged in the opposite direction.

In processes that handle ESD-sensitive devices, stability of ion balance is more important than static elimination speed.　　On the other hand, when foreign matter is to be prevented from adhering to molded resin products during transport, the static elimination speed that powerfully eliminates static electricity in a short time is more important than a slight imbalance.Designers must weigh the "electrostatic withstand voltage" and "allowable tact time" of the target workpiece to select the optimal model.

Design of optimal ionizer usage

Characteristics of high-frequency AC method

The "high-frequency AC method" is often selected for precision electronic component mounting machines and in handling equipment where space is limited.　　In this method, a high voltage of positive and negative ions is alternately applied to a single discharge needle at a high frequency, generally around 68 kHz (kilohertz).　　Because the polarity of the voltage is switched at high speed, the discharged ions become like a "cloud of ions" with a uniform mixture of positive and negative ions.

The greatest advantage of the high-frequency AC method is its extremely good ion balance.　　Since the polarity of the ions changes rapidly, the potential fluctuation (potential amplitude) of the workpiece surface can be minimized, making it suitable for static elimination of extremely small devices that are vulnerable to ESD (electrostatic discharge).　　The use of a piezoelectric ceramic element in the transformer makes it easy to reduce the size and weight of the main unit, minimizing the impact on the payload when mounted on the tip of a robot arm.

On the other hand, a disadvantage is the characteristic of "short ion reach.　　Since positive and negative ions are emitted in close proximity, they easily attract and recombine with each other, resulting in a decrease in ion concentration as soon as they leave the emission port. For this reason, if a high-frequency AC system is used, it is essential to install it at a short distance of 50 mm to 300 mm from the workpiece, or to design a mechanism that carries the ions on the air blow wind.

Selection of Pulse DC Method

The "pulsed DC method" is suitable for static elimination of an entire area from the ceiling of a clean room or for large glass substrates or films from a distance.　　This method has separate electrodes (or switching circuits) for positive and negative ions, and emits ions alternately at frequencies as low as several to several dozen hertz.

The characteristic feature of the pulsed DC method is that positive and negative ions are emitted as "clumps (pulses)" respectively.　　Since the distance between ions is maintained, recombination is difficult to occur, and ions can reach a distance of 1 meter or more even with no wind (no breeze) or light breeze.　　This makes it possible to eliminate static in processes that do not like airflow or in places where the ionizer cannot be brought close due to mechanical restrictions.

However, if the frequency is set too low, there is a risk of a "swing phenomenon" in which the potential of the object swings significantly between positive and negative.　　Using an extremely low frequency for a device with high ESD sensitivity may cause instantaneous voltage stress, even though the device is intended to eliminate static.　　Some recent models have a function that automatically adjusts the pulse width while monitoring the amount of charge with a sensor, and by utilizing these functions, both safety and static elimination performance can be achieved.

Table 2: Comparison of major voltage application methods and selection criteria

Reference source: Keyence Performance by static eliminator method (Japanese only)https://www.keyence.co.jp/ss/products/static/static-electricity/ionizer/method.jsp）

Reference source: SMC Ionizer Selection Guide (https://www.smcworld.com/catalog/New-products/pdf/s100-97b-izs40.pdf）

Bar type installation location

Bar type ionizers are the first choice when a surface static eliminating barrier is required for wide workpieces such as trays on a conveyor or rolls of film.　　The basis for selection is to choose a size that is longer than the full width of the workpiece (allowing 50 to 100 mm on each side).　　If the length is not long enough, insufficient static elimination may occur at the edge of the workpiece, from which electrical discharge and sticking may occur.

As for the installation location, the ironclad rule is "immediately after the charging occurs" and "immediately before the problem occurs.　　For example, in the film unwinding process, the bar is most strongly charged at the moment the film is peeled from the roll, so it should be placed in a position where it can be directed to the peeling point.　　For conveyor transport, bars should be placed before the film is transferred to the next process or at the entrance of the area where workers come into contact with the film.

A potential blind spot here is the relationship with the surrounding metal frame.　　Ions emitted from a bar-type electrode are attracted not only to the workpiece but also to a nearby grounded metal body (ground).　　If there is a metal cover or frame in the immediate vicinity of the bar, the ions will be absorbed there and will not reach the vital workpiece.　　When designing, care must be taken to ensure that the manufacturer's recommended isolation distance is maintained around the bar or that a model with specifications that are less susceptible to the effects of metal is selected.

Typical product series that can be used as a reference in selecting a bar type are listed below.

• Keyence SJ-H Series
  • This model combines ultra high-speed static elimination with low maintenance. The "Supersonic Structure" prevents dirt from adhering to the needle tip, making this model suitable for those who wish to reduce maintenance man-hours.
• SMC IZS40/41/42 series
  • SMC's unique "dual AC method" reduces the potential amplitude to the workpiece, which is effective when you want to minimize the influence on electronic devices. A wide range of variations are available, including controller-isolated types.
• Panasonic ER-X Series
  • In addition to supporting airless static elimination, the lineup also includes heads with heat- and cold-resistant specifications, making them suitable for use in harsh temperature environments, such as around molding machines.

How to utilize spot nozzles

The spot nozzle type is best suited when you want to perform localized static elimination as well as dust elimination by blowing off adhered dust and foreign matter.　　The power of compressed air can be used to irradiate highly concentrated ions with pinpoint accuracy, for example, inside dimpled workpieces or molded parts with complex shapes,Able to approach areas that are difficult to reach with normal bar type ionization.will be.

One specific application in automatic machine design is installation near the robot hand or suction nozzle that performs pick & place.　　By spot-blowing static eliminating air just before picking up a workpiece or at the moment it is released, pick-up errors and take-backs (defective release) can be prevented.　　Another effective use is to eliminate the bridging phenomenon caused by frictional electrification by targeting and installing in the bowl of the parts feeder where parts tend to clog.

One point to note is that constant air flow increases the running cost (electricity bill). It is recommended to combine intermittent control (pulse blowing), which detects the passage of workpieces with a photoelectric sensor, etc. and blows air only at the necessary timing, to reduce air consumption and achieve a high dust removal effect with pulse shock waves.

Typical product series that can be used as a reference in selecting a spot nozzle type are listed below.

• Keyence SJ-M Series
  • This is an ultra-compact micro static eliminator. The head part is very small and heat-resistant, making it ideal for installation in narrow spaces inside equipment or in high-temperature environments.
• SMC IZN10E series
  • A wide variety of nozzle shapes are available, including energy-saving nozzles and high-flow nozzles, depending on the application. A maintenance reminder function is also provided.
• Panasonic ER-VS series
  • This is an ultra-compact ionizer employing a high-frequency AC system. It has excellent ion balance and is suitable for static elimination of fine parts.

Relationship between installation distance and effectiveness

The ionizer's static elimination capability varies dramatically with installation distance.As a physical law, the strength of the electric field decreases inversely as the square of the distance, and the efficiency with which ions reach the target also decreases sharply with distance.　This means that the time required for ionization increases dramatically with distance.

In the early stages of design, there is a tendency to place the ionizer away from the workpiece due to lack of space, but this is often not effective enough.Basically, the ideal distance between the workpiece and the ionizer should be as close as possible (usually within 300 mm, around 100 mm if possible).

However, there are also adverse effects of placing them too close together.　　The risk is that inductive noise from the high voltage may affect the proximity sensor, or that areas of uneven ion balance (stripes) may be applied to the workpiece. If a distance must be kept, it is necessary to combine measures such as using "wind (air purge)" to forcibly transport ions or selecting a pulse DC method specialized for long-distance ionization.　　Note that a mismatch between distance and method is one of the most common design errors.

Conductive tubing piping

When using the spot nozzle type, ionized air can be directed through a tube to confined areas where the nozzle itself cannot be installed.　　At this point, the selection of the tubing material used for piping is extremely important.　　Because common polyurethane and nylon tubing is an insulator, the inner wall of the tubing itself is easily charged, absorbing and consuming the ions that pass through it.　　As a result, there is no end to the number of failed cases where almost no ions come out of the tip of the nozzle.

To prevent this from happening,Always use "conductive tubing" specified by the manufacturer or tubing made of Teflon or other antistatic material for ion transportThe longer the tube, the more the ions will decay due to collisions with the inner wall.　　Nevertheless, the longer the tube, the more inevitable the attenuation of ions due to collision with the inner wall. As a design rule, it is necessary to keep the tube length as short as possible (generally within 500 mm to 1000 mm) and to design a route with a large bending radius.

Also, if there is a sudden change in cross-sectional area of the flow path or a step at the fitting, turbulence will be generated there and ionic recombination will be accelerated.　　It is important to secure as straight a piping path as possible and to be conscious of fluid design to deliver ions "alive" to the workpiece.

Effectiveness of opposing installation

For conveying highly insulating sheet workpieces such as LCD glass substrates and plastic films,In many cases, static elimination from one side is not sufficient.　　When a sheet comes into contact with and is peeled off from the conveyance roller, charging occurs on both the front and back surfaces.　　More troublesome still, it is not uncommon for the front and back surfaces to be charged with different polarities.　　If ions are applied to the sheet from only one side, the apparent potential may be lowered, but the charge on the reverse side remains unresolved and may reappear as a strong potential at the moment the sheet is peeled off in the next process.

An effective design method to address these issues is "opposing installation.　　Ionizers (mainly bar type) are placed in the same position on the front and back sides of the workpiece as if the workpiece is sandwiched between them, and ions are irradiated from both sides simultaneously. This effectively eliminates even the effects of static electricity hidden inside.

The following manufacturer information is helpful for specific examples of opposing installations.

• Sysid Electrostatic: Examples of static elimination during transport
  • The solution introduced here prevents uneven charging and prevents foreign matter from adhering to film and glass substrates being conveyed by installing an ionizer on both the front and back sides of the substrates.

However, when performing opposing installations, care must be taken to avoid interference between opposing ionizers.　　Their ions may pass through the workpiece and affect the electrode on the other side, or disrupt ion balance control.　　To prevent this, it is advisable to offset the position of the ionizers by a few centimeters in the transport direction (offset placement), or to select a model with a synchronization function that supports opposing installation to ensure more reliable ionization.

Blind spots in ionizer usage and maintenance

Risk avoidance of reverse charging

Reverse charging is a phenomenon in which an ionizer installed with the best of intentions becomes the cause of static electricity problems.　　This is caused by an imbalance between positive and negative ions emitted from the ionizer, and an excessive supply of one polarity or the other.　　If a workpiece that is originally uncharged (0 V) is continuously exposed to unbalanced ions, the workpiece will be charged to the potential of that excess polarity (e.g., minus 200 V).

Particular attention should be paid to electronic components with small capacitance and insulated floating conductors.　　These are prone to manifest even the slightest charge imbalance as a large voltage change, which can cause ESD breakdown without being noticed.　　To prevent reverse charging, it is fundamental to measure the ion balance periodically. As a countermeasure at the design stage, it is effective to select an ionizer "with feedback sensor".

Ionizers with this function constantly monitor the potential of the object with external or built-in sensors and automatically adjust the ratio of positive and negative output to cancel out that potential.　　Even if the balance is about to be upset due to aging or changes in the ambient environment, it is automatically compensated to maintain safe static elimination over the long term.　　We strongly recommend the use of these highly functional models for processes that require reliability.

Electrode needle wear and sheath air technology

Ionizers are not "installed and done" maintenance-free devices.　The discharge needle (electrode needle), which is the heart of the product, continues to receive energy from corona discharges due to high voltage, and as time passes, the needle physically wears down and the tip becomes rounded.　　As the needle tip becomes rounded, not only does the discharge efficiency decrease and the amount of ions produced decrease, but the ion balance is also disrupted due to the difference in wear speed between positive and negative ions.

A further problem is contamination caused by airborne particulates and silicon gas that collect on the needle tip and accumulate as insulators such as silicon dioxide (SiO2).　　When these deposits adhere, the discharge is inhibited and the static elimination capability is significantly reduced.Designers should anticipate these degradations and locate the ionizer in a location that is easy to maintain (ensuring accessibility).　　If the device is embedded too deeply into the device, it will eventually malfunction due to inability to clean or change needles.

Sheathed air" is a technology that is attracting attention as a means of reducing the time and effort required for such maintenance.　　This is a structure in which clean air is blown out as a laminar flow from the periphery of the discharge needle to protect the needle tip.　　The sheath air acts as an air curtain, physically preventing the surrounding dirty air from coming into contact with the needle tip, thereby dramatically reducing the adhesion of dirt. In some cases, this allows the machine to maintain its performance without maintenance for several to ten times longer than with conventional systems.　　For automated machines that require less frequent maintenance, selecting a model with a sheathed air structure is a very effective solution.

Table 3: Comparison of electrode needle materials and characteristics

Reference source: Keyence De-energizer Maintenance (Japanese only)https://www.keyence.co.jp/ss/products/static/static-electricity/ionizer/maintenance.jsp）

Reference source: NCC Know Your Ionizer (https://ncc-nice.com/ncc-clean/trivia/gomi-ibututaisaku/ioniser-3/）

Summary of how to use the ionizer correctly

Finally, the following is a summary of important points for correctly designing an automatic machine using an ionizer. Please use these as a checklist to improve the quality of your design.

• Identify the main causes of static electricity generation (peeling, friction, induction) and take countermeasures at the point immediately after generation
• Select ion balance for electrostatic discharge (ESD) countermeasures and static elimination speed for foreign matter countermeasures (ESA) as the highest priority.
• Select the high-frequency AC method for short-distance and precision ionization and the pulsed DC method for long-distance and spatial ionization.
• For bar type, select a size longer than the full width of the workpiece to provide insulation distance from the surrounding metal frame.
• Spot nozzles are used in conjunction with intermittent control (pulse blowing) to both improve dust removal effectiveness and save energy.
• Install as close as possible to the workpiece (within 300 mm) because ion concentration attenuates inversely proportional to the square of the distance
• Be sure to select conductive or fluoroplastic tubing for ion transport, and pipe length should be 1000 mm or less.
• Highly insulating sheet materials are designed to neutralize charges on both front and back sides simultaneously by opposing installation
• When installed opposite each other, use offset placement or models with synchronization function to prevent interference between ionizers.
• Utilize automatic ion balance correction function and sensor feedback to prevent problems caused by reverse charging
• Assuming that the discharge needle is a consumable item, the design should include an arrangement (sliding mechanism and door) for easy cleaning and replacement.
• If you want to reduce maintenance man-hours, select a model with sheath air technology to prevent needle contamination.
• Use ozone-resistant materials (fluorine, silicone, etc.) for peripheral equipment in consideration of deterioration of rubber parts due to ozone generation.
• Electrical design to interlock with equipment interlock circuits to prevent ionizers from forgetting to turn on.
• Incorporate periodic effectiveness measurement (charge measurement) into the operational flow so that performance degradation can be managed numerically.

That's it.