Mar 21, 2013 - require a degree of configurability in order for them to perform .... Automotive .... varying degrees of
A BIMBA WHITEPAPER
3/21/13
How Close is Close Enough
Pneumatic and Electric Actuation to Accomplish Positioning Accuracy Authors: Gilbert Guajardo, Don Harris, and Jerry Scherzinger
• What can I use to create a repeatable 2-stage positioning system with an end of stroke hard-stop? • What can I use to create a flexible manufacturing cell that can achieve several different positioning accuracies? • How can I ensure that my electric positioning system does not lose its position accuracy? Is there a component that I can use to prevent this? • Our equipment is controlled pneumatically but I need a positioning system that can provide extreme and repeatable accuracies. What are my choices? • I have never used an electric actuator for positioning; what do I need to operate it? Positioning system design and selection requires answering a variety of application questions, as well as knowledge of available alternatives. This whitepaper provides background information and system comparisons that will allow you to choose a system that gets you “Close Enough” to where you need to be.
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How Close is Close Enough Multiple Position Cylinders
POSITION 1 FULLY
Any discussion on achieving multiple positions with a pneumatic actuator must start with the most basic and repeatable method: multiple position cylinders. Multiple position cylinders are considered to be the most repeatable method of achieving multiple stops within the total stroke length. This is because each stopping point consists of a “hard stop,” meaning further travel of the internal piston is prevented because the piston impacts the end cap at the stopping point. Later in this paper, we will discuss electronic methods to achieving multiple stopping points within the stroke length. While these methods have their advantages, they typically rely on electrical signals to control the travel of the piston, which can lead to less than perfect repeatability depending upon the electronics used. However, in the multiple position cylinder design, the piston stops on the end cap in the same place each and every time.
How it Works Multiple position cylinders differ from conventional cylinders in that they have one additional port for each additional stop position. For example, a three-position cylinder will have three ports, a four-position cylinder four ports, etc. Examples of a non-repairable three-position cylinder (on left) and a compact style four-position cylinder (on right) are shown below.
Figure 1
Starting from this fully retracted position, it is possible to extend the external piston rod assembly to the partially extended position. This (Position 2) is frequently called “Stroke A.” To complete Stroke A, compressed air should be supplied to Port 1, and the air should be allowed to exhaust from Port 3 as shown in Figure 2. As shown in the diagram, the internal piston rod assembly makes a hard stop (metal on metal) at the end of Stroke A. Because this is a hard stop, this position will be reproducible each and every cycle. POSITION 2
Each position or “stage” has its own internal piston and rod assembly. Basically, the concept can be thought of as stacking one cylinder on top of the other inside the cylinder bodies. For example, a three-position cylinder will have two piston rod assemblies that have no mechanical connection between them. For this example, we will consider Position 1 to be with the cylinder rod fully retracted. This is achieved as shown in Figure 1 by supplying compressed air to Port 3 and allowing air to exit through Port 1 and Port 2. This returns the visible piston rod to its fully retracted position and also returns the secondary, internal piston rod assembly to its home position fully retracted against the rear end cap.
Figure 2
Starting from the intermediate or “partially extended” position of Stroke A, it is then possible to fully extend the cylinder’s stroke (Position 3) by supplying air to Port 2 and allowing air to exit
Bimba Manufacturing Company from Port 3 as shown in Figure 3. The external piston rod again comes to rest against a hard stop to complete Stroke B. POSITION 3
2
To return the cylinder from Position 3 to Position 1, the opposite solenoid is energized on the 4-way valve, supplying pressure to Port 3. The solenoid on the 3-way valve is de-energized, and exhaust air is permitted to escape through Ports 1 and 2.
Figure 3
It should be noted that it is not necessary for the cylinder to complete Stroke A prior to moving to the fully extended position. Any time air is supplied to Port 2, the external piston rod assembly will move into the fully extended position. It is also possible for the cylinder to be retracted to the intermediate position with the same highly reproducible accuracy provided by the metal on metal hard stops. To achieve this “partially retracted” position, compressed air should be supplied to both Port 1 and Port 3 simultaneously. Because the available surface area on the internal piston is greater than the available surface area on the external piston rod assembly, the internal piston rod assembly will generate more force and resist being pushed back to its retracted position, providing a stable, repeatable intermediate position.
Valve Requirements The ability to supply air and allow for exhaust flow is critical to the proper operation of a three-position cylinder. There are a number of different strategies that can be employed. Here we will discuss one of the more common and simple approaches. This circuit requires a 4-way, three-position valve with an open center to be connected to Port 2 and Port 3. A solenoidoperated 3-way valve is connected to Port 1. To move the cylinder from Position 1 (fully retracted) to Position 2 (partially extended), the solenoid on the 3-way valve is energized and the valve supplies pressure that flows from the source into Port 1. Ports 2 and 3 are allowed to exhaust as shown in Figure 4, with the 4-way valve in its open center position. To move the cylinder from Position 2 to Position 3, air is continuously supplied to Port 1, and the 4-way valve is shifted by energizing the solenoid on the right side of the valve to provide pressure to Port 2 while exhausting Port 3.
Caution: Optimal operation of three-position cylinders is most easily achieved with the cylinder mounted rod up or horizontally. Because the external piston rod floats, suspending a load with the rod mounted vertically downward will complicate the required valving.
Figure 4
Multiple position cylinders are an excellent choice for applications where the discrete stop positions are predetermined and unchanging. Their design offers the highest level of repeatability at a relatively low cost. However, today’s highly automated “intelligent” machines often require a degree of configurability in order for them to perform multiple tasks. In those cases, the addition of electronics to the actuator design makes them more flexible.
Electro-Pneumatic Control Merging Pneumatics with Electronics to Provide Closed Loop Motion Control Up to this point, we described basic pneumatic end of position positioning using multi-positioning actuators with repeatable “hard stops.” The advent of merging pneumatics with electronics has expanded the use of pneumatics to provide flexible, nimble positioning control systems. These systems have resulted in better utilization of equipment, saving money and manpower by reducing and/or eliminating equipment changeover.
Cost of Changeover Changeover is one of those hidden expenses that consume time and manpower. Furthermore, it is often overlooked in calculating product cost and capacity utilization. Figure 5 was developed based upon a survey completed by Rockwell
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Automation and PMMI. It provides approximate costs associated with changeover within specific industries. Reducing changeovers can increase production throughput, improve equipment utilization, and re-allocate resources and manpower to complete other tasks. Pneumatic positioning systems create closed loop “intelligence” to the process by controlling pneumatic actuation via PLC or other types of electronic controls. Hourly cost of Downtime by Industry Sources: ARC Advisory Group, Rockwell Automation, and PMMI
$750,000
$0
Food & Beverage Plastic Rubber Paper
$1,500,000
$2,250,000
$3,000,000
$7,800
A. Internal LRT
B. Internal Non-Contact
C. External Non-Contact
Figure 6
$12,000
A magnetostrictive sensor uses a 24 VDC input voltage. However, the sensor is calibrated to provide a 0 to 10 VDC feedback voltage. The same 10 inches of stroke actuator example provided above for the LRT applies to a magnetostrictive sensor as well.
$25,000 $36,000
Electronics Metals Chemicals Pharmaceuticals Automotive Oil & Gas
$500,000
$600,000
$700,000
External non-contact sensors also use magnetostrictive technology and are simply an externally-attached version of the internal sensor described above.
$1,100,000 $1,600,000
$3,000,000
Figure 5
How it Works Pneumatic actuators are now available with either internal or external sensors that provide a constant analog or digital feedback signal based upon the position of the actuator’s rod. As seen in Figure 6, there are two types of internal sensors that run down the inside of the rod: 1. A contact sensor is a linear resistive transducer (LRT) (A) that has a mechanical wiper attached to the piston. The wiper provides a feedback signal (voltage) based upon the position of the actuator’s piston or a non-contact, magnetostrictive sensor (B) that provides the feedback signal (voltage) based upon the magnet attached to the actuator’s piston. 2. A non-contact sensor attaches to the outside of the actuator (C) and also uses the internal piston magnet to return a feedback signal (voltage). A linear resistive transducer or LRT generally uses a 0 to 10 VDC input voltage. These 10 volts are divided across the length of the LRT. Using 10 inches of stroke actuator as an example– fully retracted represents 0 volts, the first inch of stroke would represent 1 volt, 2 inches of stroke 2 volts, and so on. A full stroke of 10 inches would represent 10 volts. The LRT’s resolution, the smallest change that can be detected, is based upon the capabilities of the electronic controls. For example, a 12-bit, 4096-part controller can divide the 10 volts into 4096 parts, which equates to 2.4 millivolts or 0.0024 inches of stroke.
Sensor Comparison Chart Technology
Linear Resistive Transducer
Magnetostrictive
Sensor type
Contact
Non-Contact
Signal type
Analog
Analog
Resolution
Infinite/Operating electronics dependent
.006"
Non-Linearity
+ - 1% of stroke length
+ - .011"
Repeatability
0.001"
+ 0.006"
Accuracy
0.1"
.016"
Comment
Mechanical life affected by usage
No mechanical part – longer life
Resolution—Smallest change that can be detected by the sensor Non-Linearity—Max deviation of the voltage to a straight line Repeatability—Ability to provide the same output voltage at a unique cylinder position
What Controls the Actuator A closed loop motion control system is created by using a pneumatic valve that can receive and respond to a command signal from a PLC or other type of electronic controller, monitor the actuator’s position, and adjust the command signal to the actuator to accurately position it. Pneumatic motion control valves accept a 0 to 10 VDC or 4 to 20mA analog command signal.
Bimba Manufacturing Company Figure 7 illustrates a closed loop pneumatic system. When the valve receives its command signal it begins to supply air to extend the rod. As the rod moves, the actuator’s sensor provides a continuous feedback voltage to the valve so that the valve continues to supply air on the extend side of the actuator until the feedback voltage equals the command voltage. Conversely, as the command signal (less voltage) is supplied to the valve it opens flow to the retract side of the actuator to retract it. The valve will supply pressure to either the extend or retract port to maintain the targeted position. Some valves use built in deceleration profiles while others use advanced differential pressure algorithms with closed loop PD (Proportional and Derivative) control capabilities to prevent overshoot to achieve and maintain the positioning target.
Constant communication between the valve and actuator monitoring its position.
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Horizontal Applications
Actuator Bore Size
Vertical Applications
Average Velocity Without Overshoot at Maximum Payload [in/sec]
Average Velocity Without Overshoot at Maximum Payload [in/sec]
1-1/16"
20
70
1-1/2"
10
70
2”
15
50
2-1/2"
15
15
3"
15
20
Table 1
of the actuator’s stroke length. Using the 10 inches of stroke actuator example, a pneumatic motion control system would provide positioning accuracies of 0.10 inches. Note Table 1’s use of the term overshoot. Overshoot occurs when the combination of load and velocity exceeds the valve’s capability to stop the load at the desired position and therefore overshoots the positioning target. Air is a compressible fluid, if the combination of speed and load, along with kinetic energy is too great, the valve will not be able to react to and attain the desired position.
Common Pneumatic Motion Control Applications Constant communication between the valve and the controller.
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Quality Control
· Gauging–flexible product gauging for Go/No Go parts checking/rejection · Missing component–fastener is present and inserted to the proper depth Multi-Packaging Lines
Figure 7
•
Pneumatic positioning valves provide adjustments that increase or decrease responsiveness to the command signal, damping, or to reduce the possibility of overshoot and vertical application adjustments that provide balanced motion.
· Stop Gate/Door operation
Changing the actuator’s stroke length or the velocity with which it operates can be controlled via the electronics. The actuator will extend or retract based upon the voltage it receives and adjust its velocity based upon the speed at which the command signal is sent. Using the 10 inches of stroke example–if your process run only requires 5 inches of stroke, a 5VDC command signal extends the rod 5 inches.
•
· Damper control · Process tooling adjustment for differentiated product Valve Control
· Process/Flow valves
Pneumatic Motion Control Pros and Cons Pros
Cons
Large load carrying capabilities
Air supply between valve and cylinder longer than 10' effects performance
Pneumatic Motion Control - Accuracy, Velocity, and Load
High speed velocities
Compressibility of air can create “Overshoot” at faster velocities
A pneumatic motion control system has the capability to move large loads at high velocities. Table 1 is an example of a typical pneumatic motion control’s load carrying capabilities. The positioning accuracy for the loads and velocities shown is 1%
Accurate to 0.010"
If load requires rigid positioning then additional locking mechanism may be necessary
Closed loop control – upstream / downstream communications
Large air leakage creates abnormal valve sequencing to maintain position
Application environmental flexibility Ease of setup Medium expense
Bimba Manufacturing Company There are applications that only require end-of-stroke positioning while others require flexibility and control of large loads at a variety of speeds and position accuracies, as well as upstream and downstream process communications. An understanding of an application’s motion control requirements and the technologies capable of serving them is the focal point of this paper. Simple, end of position sensing versus closed loop pneumatic motion control and soon to be discussed electric actuation positioning have specific features that are a “better fit” than others.
Electric Actuator Positioning While multi-position and electro-pneumatic systems offer varying degrees of positioning capability and are the right positioning choice for many applications, they may not always be the ideal solution in some positioning applications that require greater precision, flexibility, and reliability. There are certainly advantages and disadvantages to each of the aforementioned positioning technologies. For extreme positioning applications with maximum flexibility, repeatability, and hence maximum reliability, electric actuators offer the best positioning solution. Next let’s examine more closely positioning using electric actuators and the advantages, as well as the limitations, for electric actuators as precise positioning tools.
Stepper Motor Drive Electric Actuators The first electric actuator we will explore is an electric cylinder driven by a stepper motor as shown in Figure 8. Stepper motors are digital input devices and are therefore particularly well-suited for the type of application where control signals appear as digital pulses. One digital pulse to a stepper motor from a stepper drive results in the motor incrementing one precise angle of motion. For a typical industrial stepper motor, this received single digital pulse causes the shaft of the stepper motor to rotate 1.8 degrees. This angle of rotation of the stepper motor is highly reliable, repeatable and accurate. Hence, for a stepper motor installed to an electric actuator with a 1/8 inch lead screw that receives 200 digital pulses from a stepper drive, the user can expect the linear motion of the electric actuator to traverse 360 degrees or one complete revolution of the motor shaft. This one revolution equates to a 1/8 inch linear travel of the electric actuator end effector.
Figure 8
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This digital pulse characteristic of the step motor is a highly reliable means of controlling shaft rotation and thus the linear motion of the electric actuator. The advanced electronics of the stepper drive results in a clean, reliable pulse train of square waves that arrives at the motor and the corresponding reliable motion of the electric actuator. Comparing this reliability to a multi-position actuator or electro-pneumatic system should be evident. A multi-position actuator can only provide a few discrete positions, and a typical pneumatic electro system with a 10 bit analog resolution is limited to 1024 discrete positions between the maximum and minimum positions. Assuming a 10 inch stroke, this means that the electronics can cause, in theory, a minimum of 0.010 inches of change in position as a result of a minimum increment. In practice, most electro-pneumatic cylinders provide about 0.1 inches of change in position when external variables such as friction are considered. Comparing this to the highly precise and well defined motion of an electric actuator, one can see from our prior example that the stepper motor controlled motion of our electric actuator can easily be controlled to 1/8 inch and, in theory, to something much less. That is, the electric actuator linear motion can be controlled to 0.0006 inches since one digital pulse from the drive will cause the shaft to rotate 1.8 degrees or one of 200 incremental moves of one complete turn of the motor shaft. For a 1/8 inch lead screw, the resulting motion from one digital pulse is 0.0006 inches. So, it is easy to see that an electric solution implementation consisting of a stepper motor can increase the precision of the positioning application monumentally. To be fair, the mechanics of a lead screw actuator such as backlash can certainly influence the minimum motion that can be accomplished. But it is not unusual for some electric actuator manufacturers to boast a backlash of 0.0006 inches or less depending on the mechanical screw technology. Additionally, stepper motors inherently provide smoother motion than electro-pneumatic systems, which naturally leads to more precise and more reliable motion. One reason for this enhanced, smoother motion is due to the advanced electronics found within stepper drives.
Microstep Emulation Most stepper drives available today provide microstep emulation. Microstep emulation is an advanced algorithm that allows the user to program an alternative step resolution for the stepper motor. That is, the standard 1.8 degree rotation per digital pulse input can be further divided into smaller rotations per pulse. In other words, a step motor will rotate 0.9 degrees in a half-stepping mode and in finer angular revolutions when the micro-stepping becomes even smaller. Typical micro-stepping drives can accomplish micro-steps of 10,000, 20,000, or even more. It is not unusual to find step drives that can provide a microstepping resolution of greater than 50,000 steps per
Bimba Manufacturing Company revolution. One can deduce, a higher micro-step resolution divides the base 1.8 degree rotation of the stepper motor into finer and finer incremental rotations. Due to this microstepping, the result is a smoother motion that provides smaller steps and the naturally smoother motion that accompanies the smaller steps. In theory, the minimal resolution for an electric actuator with a stepper motor that employs microstepping can approach a rotation of 0.007 degrees per digital pulse. This translates to a linear motion of the electric actuator of 0.000002 inches or 2µ-in. Of course, the minimal motion will be dictated by the mechanics in this scenario, but the consequence of microstepping is clearly evident in this example. It is not unusual to control motion of an electric actuator to 0.001 inches using a stepper motor. Stepper motor positioning advantages:
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Electric Actuator Motion Control Pros and Cons Pros
Cons
Fine positioning accuracy down to 0.001"
Less thrust per bore size (compared to pneumatic)
Infinite positioning
Less speed per bore size (compared to pneumatic)
Feedback to ensure positioning accuracy
Med-High initial cost
High repeatability; Minimal drift
More complex – feedback; Servo tuning
Robustly maintains load in position during motion dwell
Inherent learning curve
Scalable, flexible, configurable Can change motion parameters precisely Configurable motion is easy Clean and green; Energy efficient
•
Provides precise positioning accuracy and resolution
•
Ideal for positioning high thrust loads at low speeds
•
Outstanding repeatability
Advanced communications available
•
Digital input pulses ideal for precise positioning
Programmable
Stepper motor positioning drawbacks:
•
No feedback–could lead to positioning errors
•
Load must be static–reduces flexibility
•
In case of misstep–continues to try to position
Stepper motor with encoder advantages:
•
Feedback keeps track of shaft position
•
If positioning missteps occur, stepper motor will fault
•
Any missteps or stalling is quickly known to the user
•
Stops positioning if misstep detected–reduces waste
A stepper motor may stall as a result of some external influence including a dynamically changing load. While one may consider this stalling to be an undesired event during a critical positioning application, some prefer to consider the stall as a wake-up call that the process has changed in some fashion and that it provides an alert to investigate the process to correct it. This is important because not detecting mis-steps of the motor will result in incorrect positioning. Depending on the process, the inaccurate positioning can lead to incorrect machine or process operation which often can lead to scrap or waste. This waste is usually proportional to higher costs and leads to inefficiencies. This can be a drawback for the electro-pneumatic system when compared to electric actuator technology. To review both the pros and cons of electric cylinders, see Table 2.
Quiet Cost effective over product lifetime
Fewer connections
Table 2
Servo Motor Drive Electric Actuators What happens when the load in the process is inherently dynamic? Does this mean that an electric cylinder may not be used? No. However, it may be time to consider utilizing an alternate motor technology in the form of a servo motor. Let’s explore the characteristics of a servo motor. Consider a positioning application in which the load to be positioned may be changing, leading to new loading characteristics. A changing load characteristic can occur for many reasons including changing parts, adding new or different parts, adding new sizes, machine parts wearing out, and/or increasing throughput or capacity. As discussed, a properly sized stepper motor is an ideal solution for loads that tend to be more static in nature. In addition, a key characteristic of a stepper motor that makes it ideal for positioning of heavy loads is its inherent high torque and thrust characteristics–especially at low speeds. But, for highly dynamic positioning applications, or for loads that require relatively high speeds with large loads, a better positioning solution may be a servo motor.
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By definition, a servo motor attached to an electric actuator comes with feedback. This feedback provides an additional layer of protection or insurance to ensure that the position of your electric actuator is accurate, reliable, and repeatable. This is because the amount of error that is tolerable can be precisely configured by the operator via the servo drive. This tolerable error can be better refined to match the level of positioning required by manipulating the maximum error in encoder counts. So, one can achieve a very fine positioning accuracy using a servo motor.
servo characteristic curve. In Figure 9, there are two different curves shown: a continuous curve and a peak curve. The solid green and blue lines represent the continuous curve. The servo motor provides a very respectable amount of continuous torque capability up to 5,000 RPM. Furthermore, increased speed performance is gained when the servo motor bus voltage is increased from 24 to 48 volts. Speed performance in RPM is effectively doubled from about 2,500 RPM to 5,000 RPM. It is evident that if an electric cylinder application is selected for a high-speed application that necessitates speeds beyond about 1,500 to 2,000 RPM, a servo motor is the optimum solution.
Servo Tuning
Servo Motor Positioning Advantages
Another reason that the servo motor offers improved positioning accuracy is that the servo motor requires “servo tuning”. Servo tuning is a method by which the user optimizes the internal servo drive algorithms and electronics for controlling the torque, velocity, and position of the motor and thus the electric cylinder. In essence, servo tuning is a process of continually modifying and adjusting the servo drive output signals to the motor so the completed motion profile is achieved in the most smooth, accurate, efficient, and precise fashion within the prescribed time frame. This is another advantage for using an electric cylinder driven by a servo motor to optimize the positioning accuracy of the servo motor and the positioning application.
•
Position feedback
•
Positioning error configurable–tighter positioning tolerance
•
Adapts to changing loads
•
Capable of short bursts of peak current to improve positioning
•
Faster positioning even with larger loads
Servo Motor Flexibility - Velocity, Torque and Positioning Modes Yet another reason that the servo provides ultimate flexibility for positioning is that servo motors can be used in various modes including velocity, torque, and positioning modes. These modes provide additional functionality and offer increased levels of position control based on key operating parameters. There are typically two types of positioning modes available with a servo drive: analog and digital. Using the analog positioning mode, the servo drive is set-up to move a motor a relative distance according to the value of an analog (voltage or current selectable) input. Additionally, most servo drives offer a digital positioning mode. In this digital positioning mode, the position of the motor is determined by a digital signal in the form of pulses. This digital mode is not unlike that of a stepper motor controller, except you gain the advanced error detection capability that the servo offers. It is like getting stepper position functionality with servo precision, and is a way to get the best of both technologies within one unit.
Peak and Continuous Service Curves Another reason for implementing a positioning application with a dynamic load using a servo motor is that a typical servo motor performance graph offers two different curves. Servo motors are inherently more capable of achieving high speed at relatively high torque values over a much larger spectrum of the
Figure 9
The other curve is defined as the “peak” curve and is represented by the dotted line. It is well-defined beyond the continuous curve graph. That is, the peak curve advantage is that torque capability is up to twice that of the continuous curve. What does this peak torque do for the electric cylinder positioning application? The peak curve defines the area where the servo motor can operate at extended current and therefore extended torque, for limited time durations from about 1 second up to 10 seconds or more. The precise time period is motordependent, varies by manufacturer and motor type, and is sometimes user-adjustable. This peak area offers increased torque capability that allows the motor to more easily cope with dynamic loading applications. Due to this extended working zone, a servo motor is capable of providing short bursts of additional torque over roughly the entire speed spectrum, leading to more precise positioning control. This means that an electric actuator with a servo motor can be expected to perform
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Characteristic
Stepper motor positioning
Stepper motor w/ encoder positioning
Servo motor positioning
Comments
Cost
$
$$
$$$
Price range
Accuracy
Very good
Very good
Extremely good
Limited by mechanics
Reliability
Good w/ static loads
Very good
Extremely good
Encoder enhances reliability
Positioning
0.01" to 0.001" or better
0.01" to 0.001" or better
0.001" to 0.0005" or better
Limited by mechanics
Ease of use
Easy
Easy-medium
Medium-hard
Relative to one another
Dynamic load positioning
Good
Better
Best
Servo is made for dynamic loads
Table 3
much more reliably than either an electro pneumatic system, a stepper motor system, or even a stepper motor system with an encoder. Generally speaking, an electric actuator with servo motor will provide the most reliable positioning capability. Table 3 provides a short summary of the various electric actuator positioning technologies along with key performance characteristics.
Summary In summary, there are many ways to achieve positioning functionality using both pneumatic and electric actuators. From pneumatic multi-position cylinders, to pneumatic electro systems, to electric cylinders with step motors, to electric cylinders with step motors and encoders, to electric cylinders with servo motors, there are many options one can use for positioning applications. The best positioning solution is always dependent on the individual application and the level of positioning accuracy and repeatability one is attempting to accomplish. Other considerations include: cost, complexity, load, speed, precision, location, and similar variables. Some applications can perform and thrive using multi-position cylinders. Others require the feedback and robustness of the electro pneumatic system, while still others require the enhanced precision, programmability, and repeatability found in electric actuators. No matter what your particular positioning application may call for, the first step in selecting a positioning cylinder solution is to choose a reputable cylinder manufacturer that understands and makes available all the various positioning technologies and is able to recommend a solution that best meets the overall needs of the application.
