Selecting the right actuator for use in any manufacturing operation involves a host of application-specific variables, including aspects such as the required stroke length, load capacity, acceleration, maximum speed, and positioning repeatability. Add a cleanroom specification to the list and the choice of available options becomes significantly smaller. Consider these questions to help make the best choice for your cleanroom application, whether it’s for the medical device, pharmaceutical, biotechnology, or semiconductor manufacturing industry.
How Clean Does It Need To Be?
Different levels of cleanliness are dictated by the industries and applications involved. As an example, semiconductor manufacturing typically requires a higher cleanliness level than medical device manufacturing due to the extremely dust-sensitive nature of delicate silicon wafers. Cleanroom standards spell out both the quantity and size of particles allowed per a specific volume of air. Under US FED STD 209E — now defunct, but still widely used — a Class 1 cleanroom allows 1 particle of size 0.5 μm or larger per cubic foot of air. Similarly, a Class 1,000 cleanroom permits 1,000 particles of size 0.5 μm or larger per cubic foot, while a Class 10,000 cleanroom permits 10,000 such particles.
In contrast, ISO 14644-1 standards define the number and size of particles allowed per cubic meter of air, but have rough equivalents to FED STD 209E. For example, an ISO Class 3 cleanroom (permitting 35 particles sized 0.5 μm or larger per cubic meter of air) is equivalent to a FED STD 209E Class 1 cleanroom. ISO 6 is equivalent to Class 1,000, and ISO 7 conforms to Class 10,000. In medical device manufacturing, Class 1,000 and Class 10,000 cleanrooms are commonly used.
When specifying components for use in cleanrooms — including actuators — it is vital to know the required cleanroom classification as the first step. That said, selecting an actuator with a more stringent designation than called for by the application serves as economical insurance against unwanted particle generation. In other words, a Class 1 cleanroom actuator could easily be used in a Class 1,000 cleanroom. Note that the reverse situation may lead to problems: A Class 10,000 designated actuator should not be used in a Class 1 or Class 1,000 cleanroom. Be sure to ask your component manufacturer about certification and testing methods.
What Materials is the Actuator Made Of?
Components and systems designed for cleanroom environments must be constructed from materials that give off very few particles during use. Look for stainless steel and low-outgassing materials whenever possible, as well as those that are low-abrasion and resistant to corrosion. Consider the sealing system as well. Is the actuator securely sealed so that particles generated inside the unit during carriage motion will not enter the cleanroom? Choice of lubricant is also important. Lubricants and greases should be specifically formulated for use in cleanroom and vacuum environments. They should not emit vapors that could contaminate the workspace or finished products, such as catheters and syringes destined for medical use.
How are Particles Removed From the Actuator?
Actuators designed for cleanroom environments are typically connected to vacuum systems in order to remove any particles generated during motion. Look for units with easy-to-use connection ports. Some actuators offer specialized quick-connect ports for simple hookup to vacuum tubing, while other units offer only a threaded hole, requiring additional hardware to connect the vacuum system.
What Kind of Drive System is Used?
Many of today’s cleanroom actuators employ ball screws, while other designs use belt drives or rack-and-pinion arrangements. Ball screw units work well in many applications, but are limited to shorter stroke lengths and slower speeds than belt-driven units. Ball screw designs are typically limited to speeds of 1 m/sec. As speed and stroke length increase, ball screw US FED STD 209E was officially cancelled in 2001, but is still widely used as an industry reference. Shown here are ISO 14644-1 equivalents.
actuators generate significantly more particles than comparable belt-driven units. Due to their design, ball screw actuators are typically not sealed as tightly as belt-driven units, causing particulates to be thrown off into the cleanroom environment. In contrast, self-contained, belt-driven actuators generate very few particles, even at speeds to 5 m/s and stroke lengths of several meters. The few particles generated inside a belt-driven unit are easily vacuumed away using an energy-conscious amount of vacuum suction. Pneumatic cylinder-driven actuators are another option, but this design requires positive pressure to drive the units, potentially emitting more particulate into the cleanroom. For applications requiring longer strokes, higher speeds, and fewer particles, a belt-driven actuator is more suitable than other designs.
What Level of Position Repeatability is Required?
In the vast majority of cleanroom applications involving actuators, positioning repeatability to 50 μm is acceptable. In medical device manufacturing, for example, single-use devices are often moved from one work point to another for operators to complete different assembly tasks. Using an actuator as a conveyor of sorts can help workers avoid repetitive motion injuries while bringing speed and efficiency to manual operations. For tasks requiring more precise positioning, ask your actuator supplier about the option of adding a linear encoder.
How Will the Actuator be Used?
As lean manufacturing principles make their way from automotive into many other industries — including medical device manufacturing — engineers are beginning to look for ways to make production processes more efficient. One area involves part-handling equipment. By strategically placing actuators within assembly spaces and workstations, operator motions can be kept to a minimum to reduce worker fatigue and increase cycle times. The goal is to automate some of the manual labor involved in moving parts around, ultimately leading to higher throughput of medical devices from disposable syringes, to complex diagnostic equipment. Cleanroom actuators are well suited to this purpose.
A related aspect involves changeover times. Consider a benchtop workstation that needs to be reconfigured to assemble a variety of devices. In this scenario, it is helpful to use lightweight, compact components that may be easily moved around by assembly workers. Belt-driven actuators with aluminum profiles are easier to transport and reconfigure compared to more cumbersome ball-screw designs.
This article was written by Bob Ward, Actuator Product Manager at Rollon Corporation, Hackettstown, NJ. For more information, Click Here .