High force linear actuators: hydraulic vs roller screw actuators

Posted by Aaron Dietrich on

How to select the best high force linear actuator for your application

paper_mill needs high force linear actuators.jpgHydraulic cylinders have long been a leading choice for factory automation equipment needing a high force linear actuator. However, there have been advances in electric actuation  (for example, the availability of roller screw actuators) which make these electric actuators suitable now for many high force applications.

Industrial machine designers faced with choosing between hydraulic and electric actuation need an understanding of how each can benefit their application. This blog will review both types of high force linear actuators, hydraulic cylinders and electric linear actuators (roller screw actuators, in particular), on a variety of parameters. For a more in-depth comparison of these actuation technologies, download our white paper. 

White Paper: Hydraulic versus Electric Linear Actuators

Force

Hydraulic cylinder systems produce high forces because of their high operating pressures [1800 to 3000 psi (124.1 to 206.8 bar)]. Because Force = Pressure x Area, even a 3-inch cylinder at 2200 psi can achieve 15,000 lbf (66,723.3 kN). However, hydraulic cylinders often are oversized to improve control and may not operate at full force.

Roller screw-powered electric linear actuators can deliver forces of13,039 lbf (58,023 N) and higher and can be used in many applications that call for a high force linear actuator. A major advantage of electrical actuators is that force is instantaneous. Current passing through the servo motor produces torque that drives the roller screw and generates force. A hydraulic actuator must wait for pressure to build until force is achieved.

Control

A hydraulic actuator works well in simple, end-to-end position applications. However, applications that call for mid-stroke positioning require a more complicated set-up that includes a control valve and operator assistance.

An electric linear actuator with roller screw and servo drive/motor offers infinite control over position, velocity, acceleration/deceleration, output force and more. Adjustments can be made on the fly, plus accuracy and repeatability levels are far better than those of a hydraulic system.

System footprinthydraulic_actuator-system_components.jpg

A hydraulic system often includes a cylinder, power unit, control and accessory valves, filters, hoses and additional components. The cylinder itself offers a compact footprint at the work point, but the hydraulic power unit (HPU), which regulates oil pressure and flow, can require a lot of floor space.

An electric actuator has a smaller overall footprint with its combination of actuator, motor, and cables. The drive/amplifier is usually mounted in a control cabinet. Size requirements for an electric servo actuator system are normally a fraction of those of a hydraulic cylinder plus HPU.

Velocity

It can be difficult for both hydraulic and electric actuators to achieve high velocities at high forces.

For a hydraulic cylinder to achieve high speeds at higher forces, there must be enough pressurized oil in the system to push the specified volume of oil in the cylinder in the required amount of time. There often must be an accumulation system to hold the pressurized volume.

The force capabilities of an electric actuation system depend on the right combination of motor RPM, motor torque and screw characteristics. As servo motors increase in size, torque increases significantly but RPMs decrease. This limits speed. However, an electric actuator has control over the motion profile and doesn’t have to stroke the entire length of each cycle. Also, an electric roller screw linear actuator may be able to deliver the peak velocities required since it can execute shorter, more intelligent moves.

Sensitivity to temperature

Hydraulic systems are sensitive to temperature. The oil in these systems gets thicker and slower-moving in the cold resulting in sluggish and inconsistent actuator performance. In hiindustrial thermometer.jpggher temperatures caused by overheating or the environment, oil may degrade and seals fail. Both conditions may require additional system components and additional cost. A tank heater can maintain operating temperature in the cold. A heat exchanger can mitigate overheating.

Electrical actuation systems are much less temperature-sensitive. Due to higher efficiency, electric systems can be selected to run at a desired temperature for the given amount of work required. Accurately predicting temperature allows the electric actuation system to perform consistently without affecting the life of the device. Electric devices can be specified with optional extreme temperature grease for fast response in the cold.

Life and maintenance

Hydraulic cylinders are rugged devices that offer long service life when maintained properly. However, maintenance requirements (new seals, oil and filters) can mean machine downtime and added cost.

If the electric linear actuator is sized correctly for the application, there is no maintenance required so there is no downtime. Proper roller screw actuator selection starts with accurate calculation of actuator life. For correct sizing, rely on our sizing software.

Data collection

Manufacturing management is very interested in monitoring and measuring all Data_visualization_process_v1.pngaspects of production performance. This has given rise to the need for data collection at the work point.

When it comes to hydraulic actuation, only expensive, complex servo-hydraulic systems with additional sensors can track and monitor position, velocity, force, etc. at the work point. Standard hydraulic actuation systems don’t have data collection capabilities.

Sensing capability is built into an electric actuator’s servo system. Motor current monitoring tracks force and repeatability. The motor’s feedback device registers position and velocity.

Electricity costs

Hydraulic systems are typically 40-55% efficient in converting electrical power to motion. The HPU needs to be powered up to keep the hydraulic system energy costs by actuatortechnology.jpgpressurized whenever the system is on. The result is inefficient use of power.

Electric linear actuator systems typically operate in the 75-80% efficiency range. The actuator at rest requires no current or very low amounts of current to hold its position.

Environmental risks

Hydraulic actuation systems are prone to oil leaks that can create safety hazards, contaminate products and pollute the environment. Clean-up can be costly and time-consuming.

Electric actuation is one of the cleanest linear motion technologies. Grease on the roller screw is the only potential contaminant, and special greases (food grade, clean room, etc.) can be specified. Seals keep grease inside the actuator, virtually eliminating contamination issues

To summarize

When you need a high force linear actuator, consider all these factors carefully. While hydraulic actuation systems may be appropriate for simple motion profiles with high force requirements, an electric actuation system can offer many advantages for complex linear motion. As a machine designer you’ll want to look beyond force capabilities to consider relevant factors like footprint size, control capabilities, velocity, data collection, efficiency, maintenance, temperature sensitivity and the hazards of leaks.

For more information on electric and hydraulic actuators as they relate to these factors, see our white paper: Electric rod actuators vs. hydraulic cylinders: A comparison of the pros and cons of each technology. Download it here. 

White Paper: Hydraulic versus Electric Linear Actuators

And contact an expert like Tolomatic. We’re here to help.

Topics: Actuator selection

Electric actuator life in units of time: ball & roller screw actuators

Posted by Aaron Dietrich on
A machine’s useful life depends on the life of its critical components. And machine Ball screw Actuators_in_machine.jpgdesigners  frequently hear the question, “How long can I expect this machine to keep working?”

When electric linear actuators are used, calculating life can be straight-forward for ball screw and roller screw actuators.  Since these screw types incorporate rolling elements as essential parts, you can use the L10 life formula for ball bearings.

For a thorough explanation of how to use the L10 life formula when estimating electric actuator screw life, see our newest guide, Actuator Life: How to estimate for ball and roller screw actuators. Get your copy here. 

Actuator Life Guide

Distance versus time

The result of an L10 life calculation is in inches or milllimeters of travel. This is useful information; however, the individuals asking you how long your machine will last probably want the information in units of time, like days, months or years.

(Of course, L10 is a theoretical calculation of life based on load. As a seasoned designer, you’ll also consider the many other factors that can affect actuator life like the environment and alignment.)

This blog will show you how to convert an L10 result to units of time. But first a quick review.

Linear actuator Lead-ScrewsImportant terms

Dynamic Load Rating (DLR): Provided by the manufacturer and represented by the letter C. DLR is a constant load under which a ball bearing device will achieve 1 million revolutions (rotations) .

Constant load:  A load that doesn’t change during the working cycle.

Varying Load:  A load that changes during the working cycle.

Equivalent Dynamic Load:  Must be calculated when an application has a varying load. It’s a dynamic load which, if applied constantly, would have the same effect on screw life as the combined actual loads. Represented by the symbol, Pe.L10_life for electric actuators

L10 (or B10) Life: L10 life for a group of identical screw actuators operating under the same conditions is the number of revolutions which 90% of these actuators have the statistical probability to achieve (or at which 10% can be expected to fail).

Here are the basic formulas.

L10 life with a constant load

L10 = (C/Pe)3 x l

C = Dynamic load rating (lbf) or (N)

Pe = Equivalent load (lbf) or (N) = constant load

l = Screw lead (in/rev) or (mm/rev)

L10 life with a varying load

First, calculate the Equivalent Load, Pe:

Pe = 3 √{ [L1(P1)3+L2(P2 )3+L3(P3 )3+Ln(Pn )3]/L}

Pe = Equivalent load (lbs) or (N)

Pn = Each increment at different load (lbs) or (N)

L = Total distance traveled per cycle (extend + retract stroke) (L = L1 + L2 + L3 + Ln)

Ln = Each increment of stroke (in) or (mm) at different load

Then use the calculated Pe in the life calculation formula: L10 = (C/Pe)3 x l

estimating ball screw and roller screw actuator life in timeHow to estimate actuator life in time

Here’s what you need to know for this calculation:

L10 life calculation in distance  

L          total distance traveled per cycle (extend + retract stroke)

CpM   Number of cycles per minute  

HpD    Number of hours operated per day

DpY    Number of days of operation per year

Put that information into one of these formulas:

Life Estimate in Years =

(L10 / L) / [(CpM) X 60 min/hr X (HpD) X (DpY)]

 

Life Estimate in Days

(L10 / L) / [(CpM) X 60 min/hr X (HpD)]

This gives you the estimated life of the ball screw or roller screw actuator in units of time.

Now you can begin to answer the question “How long can I expect this machine to keep working?”  In an upcoming blog we’ll consider comparing actuators for an application.

To learn more

Download our new guide, Actuator Life: How to estimate for ball and roller screw actuators.

Actuator Life Guide

Topics: Actuator selection

Solid-bearing, belt-driven linear actuator handles harsh environment

Posted by Nick Holmgard on

PulpAndPaperMill.jpgMany applications call for the carrying action of a rodless electromechanical actuator. And many of these need the high speed and long stroke capabilities of a belt-driven linear actuator. But what do you do when your application is in a dusty, harsh environment? Many rodless electromechanical actuators can’t handle these conditions. Their roller bearings get clogged with dust and stop working. Could a solid bearing be the solution?

When you need general advice on specifying rodless electromechanical linear actuators, look to Tolomatic.  Our 10 tips white paper provides the information you need.     Download it here.

  Selection Tips White Paper Rodless Electric Actuators

Read further to learn how one user solved the problem of handling a harsh environment with a rodless actuator.

Harsh environment causes problems

Paper making creates tough environmental conditions for automation equipment. Water, chemicals and wood dust combine to challenge machinery. Designers who work for this industry have to take these factors into account in order to develop long-lasting, hard-working production systems.

We recently worked with the designer of a paper processing machine to develop a new roller-cleaning mechanism. In earlier machines, pneumatic rodless actuators powered the brushes that cleaned pulp from the paper-making machine’s rollers. These actuators failed frequently because pulp particles caused seal failures. The on-going maintenance the pneumatic actuators needed was very costly.MXB-S_in_pulp_and_paper.jpg

The machine designer wanted to use an electromechanical actuator to avoid the problem of seal failures in pneumatic actuators. The application had a stroke length of over 100 inches (2540mm), making a belt-driven actuator the best choice. However, many of the belt-driven electromechanical actuators that were considered had roller bearings on their carriers. Pulp particles got into the roller bearings, clogging them and leading to actuator failure.

Solid bearing is the solution

MXB-S solid bearingThe machine designer worked with Tolomatic to find a solution – our new MXB-S electric belt-driven linear actuator. The MXB-S with its unique solid bearing replaces the previously-used pneumatic actuator that was causing failures and high maintenance costs. This new rodless actuator’s solid bearing is self-cleaning. It easily pushes pulp away as it moves the carrier back and forth on the actuator body. The end of the actuator is left open so moisture and pulp particles can be pushed out. A stainless steel gearbox and motor power the actuator. Stainless steel was selected to withstand the wet environment.

The MXB-S delivers reliable performance and increased actuator life in this application. Plus, there’s less down time, and maintenance costs are lower.

Introducing the new MXB-S

MXB-S_Features.jpgThe MXB-S belt-driven linear actuator is the newest member of the MXB rodless electromechanical actuator series. The series includes the MXB-U unguided belt-driven linear actuator and the MXB-P heavy duty linear actuator with profiled rail carrier bearings. The MXB-S features a trapezoidal, self-cleaning solid bearing system for the carrier, a bearing system that is field-replaceable.

The MXB-S is a good choice for applications in harsh environments like paper production or sawmills because of its long-lasting, self-cleaning bearing. It is also well-suited to applications requiring light to moderate load carrying and guidance. long-stroke linear actuator MXB-S.jpgThis low-cost linear actuator offers speeds of up to 100 in/sec (2540 mm/sec) and thrusts of up to 418 lbf (1860 N). The MXB-S is a long stroke linear actuator that is available in stroke lengths of up to 200 inches (5080 mm).

Download the MXB catalog here.

MXB Catalog

For more information

To learn about specifying rodless electromechanical linear actuators, download our 10 tips white paper.

  Selection Tips White Paper Rodless Electric Actuators

When the choice between screw-driven and belt-driven linear actuators isn’t obvious, see our white paper for helpful information: Screw-driven vs. belt-driven rodless actuators: How to select drive trains for reliability, efficiency and long service life. Download it here.

White Paper: Belt Driven vs Screw Driven Rodless Electromechanical Actuators

Topics: Linear Actuator Application Tips

Selecting a rodless electromechanical actuator: belt- vs. screw-driven

Posted by Igor Glikin on
Screw-Driven and Belt Driven ActuatorsLet’s say you’ve decided you need a rodless electromechanical actuator to carry a load in your application. Now you have to select a linear drive system. The two most common choices are screw drives and belt drives. Both drive types offer long life, low maintenance and efficiency in converting the motor’s rotary motion to the carrier’s linear motion. However, each drive type is more suited to particular applications than others, depending on a few key factors.

This blog will review the advantages and disadvantages of these linear drive systems. For a detailed explanation, download our white paper.

White Paper: Belt Driven vs Screw Driven Rodless Electromechanical Actuators

The key factors you’ll need to consider in your drive train choice are:

Let’s take a closer look at each of them.

Accuracy/repeatability

Accuracy is the ability of an actuator to achieve a specified position. Repeatability is the ability of an actuator to achieve a position time after time. Each application will have its own requirements for accuracy and repeatability.

A screw-driven linear actuator’s accuracy/repeatability performance depends on ball_screw-1.jpgthe screw type and the method in which the screw and nut were manufactured. For example, actuators with precision-rolled ball screws can combine very good accuracy and repeatability with an affordable price. Acme (lead) screws often offer a lower level of accuracy at a lower cost while roller screws (uncommon in rodless electromechanical actuators) offer the highest accuracy with an accompanying high price

A belt-driven linear actuator will deliver lower levels of accuracy due to the variations in the belt material.

Length of stroke

The length of the stroke of a screw-driven linear actuator is often limited by the available length of the screw stock. Screw-driven actuators are most often used in stroke lengths of less than 120 inches.

Screw length and speed are related. Critical speed (see below) decreases as screw length increases.

Belt drives, on the other hand, can reach very long lengths without affecting speed. In fact, the length of a belt drive is limited only by the ability to tension a long belt. Belt-driven linear actuators can achieve stroke lengths of over 200 inches (5080 millimeters).

Velocity

screw_whip.jpgThe speed at which a screw-driven linear actuator travels is limited by the critical speed value of the screw. The critical speed is a rotational speed that approaches the system’s natural frequency, leading to resonance and vibration (also known as “screw whip”). Screw whip can lead to actuator malfunction and catastrophic failures. Screw-driven linear actuators typically operate at no more than 60 inches per second (about 1500 mm/second).

Belt.jpgBelt-driven linear actuators are not limited in this way and can achieve speeds of 200 inches/second (5080 mm/second).

Orientation

There are several ways a linear actuator can be mounted depending on the orientation of the required move:Lead-Screws_lo_res.jpg

  • horizontal
  • side
  • incline
  • vertical

Of these, vertical orientation and some incline orientations can present problems resulting from back driving (the tendency of an actuator carrier plus load to free fall due to gravity). Actuators with Acme screws of certain leads are resistant to back driving because of a higher coefficient of friction between the nut and screw threads, but a ball screw actuator will require a brake to prevent back driving in the event of a power loss.

Belt-driven linear actuators are susceptible to back driving as well and must have emergency brakes for the same reasons.

In summary

Some applications make it easy to choose a linear drive system. Belt-driven linear actuators are ideal for long-stroke applications requiring high velocity and acceleration. If the application’s stroke length and speed requirements are moderate but the accuracy level required is high, then a screw-driven actuator is best.

When the choice isn’t obvious, see our white paper for helpful information: Screw-driven vs. belt-driven rodless actuators: How to select drive trains for reliability, efficiency and long service life. Download it here. 

White Paper: Belt Driven vs Screw Driven Rodless Electromechanical Actuators

And contact an expert like Tolomatic. We’re here to help.

Topics: Actuator selection

Electric linear actuator is clean-in-place, washdown ready

Posted by Nick Holmgard on
cleaning.jpgStringent regulations govern the food processing industry. Food processing equipment and components, like electric linear actuators, must meet food safety regulations and stand up to clean-in-place (CIP) procedures. Food industry cleaning procedures may include regular washdown with hot water, steam, high pressures and caustic chemicals. Corrosion resistant materials and a water-shedding design are musts.

Need to know more about how to select an electric linear actuator for a food and beverage industry application? Get our whitepaper.

Evaluating linear actuators  for food and beverage  processing

CIP or COP: Clean is critical

clean_in_place.jpgFood processing equipment can be cleaned-in-place (CIP) and cleaned-out-of-place (COP). CIP systems can clean even interior surfaces of difficult-to-move equipment. COP methods clean equipment or components that cannot be cleaned where they’re used. Either method lets food producers keep production equipment clean and sanitized. The type of cleaning method used has to take both the equipment and the food product into account. The goals are to maximize cleaning/sanitizing effectiveness while minimizing the amount of time cleaning procedures take.

With the advent of the Food Safety Modernization Act (FSMA), there is more emphasis on sanitary design in food plants. Equipment manufacturers are focusing design efforts on making food processing equipment easier to clean and sanitize and better able to stand up to CIP and COP processes. Linear actuators used in food processing equipment need to handle the rigors of regular cleaning and sanitizing procedures without diminished performance, effectiveness or life expectancy.

Wanted: Electric actuator to stand up to washdowns

As part of the dairy industry, cheese production has some of the strictest regulations for cleanliness and food safety. When a cheesemaker was looking for a linear actuator to push cheese blocks out of molds, they needed an actuator that would not introduce any contaminants into the food and could withstand high pressure, high temperature washdowns. The producer knew a hydraulic cylinder wasn’t appropriate because of the high probability of leaks. A pneumatic cylinder was rejected since there wasn’t an existing pneumatic power system in the plant. An electric linear actuator seemed the best solution.cheesefactory-floor.gif

Electric actuator solution found

The cheesemaker asked Tolomatic for assistance. We recommended the USDA-approved ERD25 electric rod actuator. This electric linear actuator is constructed of stainless steel and is IP69K rated to stand up to the harshest conditions. Its hygienic design is approved by the USDA for use in dairy, meat (livestock) and poultry processing. The ERD25 actuator for this application has a longer than standard stroke to release cheese blocks from larger molds.

The ERD25 delivers the hygienic design the producer needs, plus it handles washdown procedures without the need for expensive shielding. Because it is fully programmable, the ERD25 offers greater control over position and speed.ERD_SS2_and_USDA

USDA ERD electric cylinders

ERD electric cylinders are well-suited to food processing industry requirements. The ERD product family includes the IP69K, USDA-approved design in three sizes (22, 25 and 30). These models feature stainless steel housings and fasteners, a water-shedding design, corrosion resistant seals and gaskets and food grade lubricants. They are washdown ready and clean-in-place compatible. No shielding is needed, so machine design’s streamlined and costs are reduced.

ERD actuators can be paired with many stepper or servo motors to create flexible, powerful, cost-effective electric actuator systems. See our video for ideas on how these actuators can be used. 

Download our ERD series catalog here.

ERD Catalog

Learn more

Download our white paper on selecting electric linear actuators for the food processing industry. 

Evaluating linear actuators  for food and beverage  processing

Topics: Actuator selection, Actuators in Food and Beverage Processing

Linear actuator helps convert conveyor to electric

Posted by Nick Holmgard on
conveying.jpgEvery factory relies on some kind of conveying system to take components, work pieces or finished goods from one place to another. In fact, most factories have several conveying systems, each tailored to a specific need. Conveying equipment is varied and essential. Components in these systems, like linear actuators, must be able to meet these varied needs and provide reliable performance.

We’ve worked with many manufacturers of conveying equipment, matching linear actuator solutions to each application. Read a case study about how we worked with a global conveyor manufacturer to meet their need to develop an electric option for their product.

Conveying equipment case study

But that’s not the whole story of our involvement in this industry. Here’s how we solved another manufacturer’s challenge.

The need: Convert to electric

A conveying machinery builder was using pneumatic actuators in diverting systems. However, the manufacturer wanted to offer an electric conveying system to meet conv-002_erd-1.giftheir customers’ requests for greater control and programming flexibility. That new electric system required an electric actuator solution.

The existing machine design had proprietary controls that operated the pneumatic cylinder. These controls couldn’t be redesigned, and the manufacturer wanted a solution that could be retrofitted in the field. That meant a new actuator control system was needed in addition to an electric actuator. The controller needed to work with both electric and pneumatic models to allow for retrofitting.

The answer

The ERD electric cylinder with ACS stepper drive was chosen as the answer to this challenge.  The ERD is a low-cost actuator for pneumatic replacement. Its compact design fits the available space in this conveying equipment so no redesigning has been necessary. Its stainless steel construction means the ERD is sturdy and reliable. Fully programmable, the ERD can be tailored to changing application needs.

The ACS is a driver/controller specially designed for linear actuators. For this ERD-features.jpgconveying system, a new Pneumatic Mode was added to the ACS software. It allows the ERD electric cylinder to mimic the operation of a pneumatic cylinder.  With the combination of the ERD electric linear actuator and the ACS, this conveying equipment builder can now market an all-electric machine. Future expansion is also possible since the ACS offers infinite positioning through its Ethernet/IP option.

ERD and ACS

Our ERD electric actuators offer a range of body sizes, screw options and stroke lengths. They create flexible, powerful, cost-effective linear motion solutions and can be paired with stepper or servo motors. ERD electric cylinders are appropriate for sorting, diverting and product change-over applications.

Download our ERD series catalog here. ACS_features.jpg

ERD Catalog

Our ACS driver/controllers are available for both servo motors and stepper motors. They are often paired with ERD electric linear actuators to create straight-forward, cost-efficient linear motion systems.

Get our ACS catalog here.

Download the brochure

Learn more

Download our conveying equipment case study.

Conveying equipment case study

Topics: Actuator selection, Actuators in material Handling

“How long will this linear actuator last?”

Posted by Aaron Dietrich on
“How long will it last?” Every machine design engineer gets asked this question and Actuators_in_machine.jpgwill have to calculate the anticipated life of the machine – life that’s based on machine components including linear actuators. Engineers also have to consider expected life when they’re evaluating competing components.

Calculating linear actuator life can be straight-forward for ball screw and roller screw actuators using the L10 life formula for ball bearings.  The life calculation focuses on these rolling elements because the screw/nut combination is an actuator’s critical moving component. Our newest guide explains all the calculations.  Get your copy here.

Actuator Life Guide

Definitions

Lead-ScrewsLet’s start with definitions of critical terms you’ll need to know.

Dynamic Load Rating (DLR): This is a number that represents a constant load under which a ball bearing device will achieve 1,000,000 revolutions (rotations) of rated life. It is usually provided by the manufacturer and represented by the letter C.

Constant load:  This is a load that remains unchanged along the full working cycle.

Varying Load:  A load that changes during the working cycle.

Equivalent Dynamic Load:  When an application has a varying load, you have to calculate the equivalent dynamic load or Pe.

Equivalent dynamic load is a dynamic load acting on the screw which, if applied constantly, would have the same effect on screw life as the combined actual loads.

In the case of constant load, equivalent load = actual load

L10 (or B10) Life: L10 is a calculation of life at which 10% of bearings in the same application can be expected to fail due to classic fatigue failure. L10 life for a groupL10_life.jpg of identical screw actuators operating under the same conditions is the number of revolutions (or distance of travel) which 90% of these actuators have the statistical probability to achieve.

This calculation provides a theoretical life estimate based on a collection of statistics. This is not a guarantee of performance but a guide for expected life.

How to calculate L10 life with a constant load

To estimate life with a constant load, the underlying formula is:

L10 = (C/Pe)3 x l

C = Dynamic load rating (lbf) or (N)

Pe = Equivalent load (lbf) or (N

l = Screw lead (in/rev) or (mm/rev)

For example, in a case where:

C = 10,000 lbf

Pe = 5,000 lbf

l = 5 mm

L10 = (10,000/5,000)3 x 5 =

(2)3 x 5 =

8 x 5=

40 =

40 million mm

How to calculate L10 life with a varying load

When a load varies during the working cycle you first have to calculate the equivalent dynamic load (Pe). Here’s the formula:

Pe = 3 √{ [L1(P1)3+L2(P2 )3+L3(P3 )3+Ln(Pn )3]/L}

Pe = Equivalent load (lbs) or (N)

Pn = Each increment at different load (lbs) or (N)

L = Total distance traveled per cycle (extend + retract stroke) (L = L1 + L2 + L3 + Ln)

Ln = Each increment of stroke (in) or (mm) at different load

Then you can use the calculated Pe in the life calculation formula:

L10 = (C/Pe)3 x l

See our new guide for examples of how to use this formula. And watch for a future issue of this blog where we’ll explain how to compare the L10 life of two actuators and how to estimate life in units of time (days, years) rather than distance.

Learn more

Download our new guide, Actuator Life: How to estimate for ball and roller screw actuators. 

Actuator Life Guide

Topics: Actuator selection

Hydraulic linear actuator advantages and disadvantages

Posted by Aaron Dietrich on

hydraulic actuatorHydraulic cylinders are popular automation components in many industries. Like other types of linear actuator (pneumatic and electric), they are used to move loads in a straight line. A hydraulic actuator uses the energy in a pressurized liquid, usually oil, to achieve this linear motion, as opposed to compressed air (pneumatics) or electricity.

Standard hydraulic actuators perform well in applications that require basic, end-to-end motion. However, as motion profiles get more complex, standard hydraulics have difficulties. A complex motion profile usually needs a costly servo-hydraulic actuation system or an electric linear actuator. In fact, many engineers are turning to electric actuators since new models can deliver the high force once thought possible only with hydraulics.

Our newest white paper compares hydraulic and electric actuator technologies. Download your copy here. 

White Paper: Hydraulic versus Electric Linear Actuators

There are pluses and minuses to using hydraulic actuators. Let’s take a look at them.

Hydraulic advantages

Hydraulic linear actuators are popular for good reason.

  1. High force capabilities

The ability of a hydraulic actuator to deliver high force is a leading reason for the popularity of this technology.  High pressures allow smaller cylinders to reach very large forces. For example, 3-inch and 5-inch bore cylinders at 2200 psi can achieve approximately 15,000 lbf (66,723.3 kN) and 43,000 lbf (191,273.5 kN), respectively.

  1. Simple design

Hydraulic actuator technology is well-understood, and cylinder design is straight-forward. Many engineers are quite comfortable using hydraulics.

  1. Rugged construction

Hydraulic actuators have a reputation for being tough enough to withstand harsh conditions. They can be durable and reliable when deployed in the right applications.  Their robust design means they can handle shock loads.

  1. Affordable

The initial purchase price of hydraulic cylinders is usually low.

Cutaway welded hydraulic actuator

Hydraulic disadvantages

  1. Limited motion control capabilities

When multiple stops and changes in velocity are part of the motion profile, hydraulic actuators have problems. Also, position, speed and force consistency are subject to worn seals, leaks and pressure changes from the pump.

  1. Inflexibility

Basic hydraulic actuators are not programmable.  Changes in force, velocity and other variables are made through time-consuming manual adjustments which may be imprecise. Servo-hydraulic actuation systems are programmable but they have more components that add complexity, space and cost.

  1. Inadequate data collection capabilitieslinear actuator data_collection comparison

Data collection and reporting  are prevalent in many manufacturing environments as part of a continuous improvement process. Hydraulic cylinders need expensive, complex servo-hydraulic systems with additional sensors to track and monitor what’s happening at the work point.

  1. High maintenance

Hydraulic actuators are rugged devices, but they require frequent maintenance and attention to perform well. Maintaining the integrity of the rod and piston seals is key because these are the main elements that contain pressure. Changing oil filters and oil must be done periodically since contaminated or degraded oil hurts system operation.

  1. Low operating efficiency

Hydraulic actuator systems typically operate in the 40-55% efficiency range. While this is better than that of pneumatic actuators (10-20%), it is much lower than that of electric actuators (75-80%). Additionally, hydraulics require that the power unit keep the hydraulic system pressurized at all times when the system is turned on—resulting in inefficient use of power.

  1. Large system footprint

A hydraulic actuator system's components take up valuable space.  Even though hydraulic cylinders offer a compact footprint at the work point,  the hydraulic power unit (HPU) that regulates flow and pressure to cylinders requires a large amount of floor space. Systems include the cylinder, the power unit to provide oil pressure, control and accessory valves, filters, hoses, fittings, and additional components.

  1. Temperature sensitivity

Both hot and cold temperatures affect the performance of hydraulic cylinders.  Heat can destroy seals resulting in loss of pressure. Cold temperatures will thicken the system’s oil and slow response.

Study your application and all its requirements carefully before you settle on an actuation technology. If you need a programmable, efficient, low-maintenance actuator that can handle a complex motion profile, consider an electric linear actuator. 

A later edition of this blog will compare hydraulic and electric actuation. Plus, our white paper gives you an in-depth comparison.

Learn more

Download our white paper that compares hydraulic and electric linear actuator technologies.

White Paper: Hydraulic versus Electric Linear Actuators

Topics: Actuator selection

Webinar: tips on electric rod actuator selection

Posted by Nick Holmgard on
rod-style_actuators webinarWhen you’re called on to specify electric linear actuators, one of the critical decisions you’ll face is whether to use a rodless or rod-style model. Either actuator type has advantages and disadvantages.

In general, if the actuator has to carry a load, a rodless product is what you need.  However, if a load needs to be pushed or pulled, select a rod-style actuator. 

 

Once you’ve decided on a rod-style  actuator, you’ll need to consider several factors to ensure you select the best model for your application. A webinar by Tolomatic offers an excellent review of these factors.

You also can download our white paper: How to specify electric rod-style actuators for optimal performance, reliability and efficiency.

White Paper: Electric Rod Actuator  Selection Tips

Consider this

It takes careful thought and calculation to select the best electric rod actuator for an application. That upfront thinking will ensure maximum reliability and efficiency from the device. Here are our ten tips to help you through this analysis when you’re specifying electric rod actuators:

  1. Calculate the loads precisely. 

You’ll need to know the static and dynamic loads to accurately specify the motor, screw or bearing. The system may fail if its components can’t handle the loads.

  1. Calculate for electric, not fluid power.

It’s common to over-size the actuator when specifying pneumatic and hydraulic models. The purchase linear actuator sizing_softwareprice of a fluid power cylinder often is not a huge factor so over-sizing can seem like inexpensive insurance.  However, the cost impact of over-sizing electric rod actuators is significant.  The cost of the actuator will be higher, and you’ll need to purchase a larger motor and more. (Electric actuator sizing software can help you get around this problem.)

  1. Know the duty cycle.

Duty cycle is defined as a ratio of operating time to resting time of an electric actuator expressed as a percentage. An actuator that is moving for two seconds and stopped for two seconds has a duty cycle of 50 percent. Underestimating the duty cycle can lead to premature failure while overestimating may lead to over-sizing and higher costs. Also, duty cycle is used to calculate the L10 life of a ball or roller screw actuator.  (Download our new Guide to calculating actuator life here.)

Actuator Life Guide

  1. Understand force and velocity requirements.

These factors combine to affect motors, screws, and nuts in electric rod actuators. An incorrect or incomplete understanding of these variables could lead you to specify the wrong components. If components can’t handle the application’s force and velocity, the motion control system may under-perform.

  1. Avoid side loading or add proper guides. 

Electric rod actuators are prone to damage and wear when they have to deal with even moderate side loads. Side loading can deflect the rod and make the actuator less accurate. Guides and appropriate mounting ensure that the rod and load are accurately aligned.

  1. Set speed limits.

In manufacturing going faster often means that more can be produced in less time. But operating at a speed that's too fast can cause trouble. For example, if the stroke speed of the electric linear actuator goes over the critical speed of the lead screw, the resulting oscillation of the screw puts stress on the support bearings and can even cause system-wide failure.

  1. Match the actuator’s peak thrust to the application.

If an application calls for a given peak thrust and the actuator manufacturer’s thrust curve says the model cannot achieve it, believe the thrust curve and find a model that matches your requirements.

  1. Understand the application’s accuracy and repeatability accuracy_and_repeatability_in_linear_actuators.jpg

High accuracy can come with a higher price tag so be sure it’s really what you need before you pay for it. You may be able to save money and build an effective, efficient motion control system by looking for a high degree of repeatability instead. You will avoid excess costs and design a system with the best overall value if you take time to understand the specific needs of your application.

  1. Factor in the environment.

Heat, cold, vibration, dust, and washdowns all affect a linear actuator’s performance.  You may need to spec the right IP rating if the linear actuator has to deal with dust or moisture. 

  1. Keep total envelope size in mind.

There’s a difference between the overall length of an electric actuator and its working stroke length. Keep both in mind or your electric actuator system will not fit the space allowed. At the same time, select a drive system that has the power you need. Reverse-parallel motor mounting saves space but can’t match the performance of an inline drive system. If you specify a linear actuator system solely on its footprint, you may wind up with a system that under-performs.

electric rodstyle actuatorsThese are the many factors that go into the design of a motion control system. If you take the time to analyze the variables and component specifications carefully in the early stages of your project, you’ll create a system that’s long-lasting, economical, and effective.

Learn more

Download our white paper: How to specify electric rod-style actuators for optimal performance, reliability and efficiency. (Insert CTA)

Topics: Actuator selection

Hygienic linear actuator keeps it clean

Posted by Nick Holmgard on
The world of food production and packaging is broad, varied and ever-changing.supermarket_shelves.jpg That world needs filling machines as diverse as the range of food products they process. Some filling machines have to handle powders and dry solids while others must handle thin or thick liquids. Some machines fill to a specified level, and some fill by volume or weight. This wide variety of equipment has a unifying need, though -- a need for hygienic design that can keep food products uncontaminated and withstand even the most stringent cleaning procedures.

Linear actuators are important components in many filling machines. We’ve documented the critical factors to consider when selecting linear actuators for food and beverage processing in our white paper. Click here to get your copy.

  Evaluating linear actuators  for food and beverage  processing

Filling equipment needs hygienic actuators

We recently helped a food processing equipment manufacturer who needs this kind of hygienic design in their linear motion system. The manufacturer was responding to customer demands that resulted from the recently enacted Food Safety Modernization Act (FMSA).

The FSMA requires that food producers:

  1. Analyze their operations for potential biological, physical and chemical hazards to their food products
  2. Take steps to eliminate those hazards

As a result, food processors are establishing regular cleaning routines to eliminate the contamination hazards they’ve identified. Food processing equipment and its components must be designed for these washdown environments.

The equipment manufacturer we helped makes filling lines, cup machines and conveyors for the food industry. They wanted to replace pneumatic cylinders in their bench-top filling machine with hygienic electric actuators for a variety of reasons.  Their customers demanded greater flexibility, accuracy, speed and energy efficiency, characteristics only electric actuators can deliver. Also, the equipment manufacturer needed a hygienic, clean-in-place compatible actuator solution since the filling machines had to meet stringent cleanliness requirements, including frequent washdowns.

To meet FSMA requirements, the filling equipment manufacturer needed electric linear actuators that were:

  • Designed to shed water and cleaning solutions
  • Without niches or crevices to trap contaminants
  • Constructed of corrosion resistant materialsvolumetrict-app.gif
  • Manufactured to meet IP69K standards

Solution

The manufacturer’s engineers consulted with our product experts who recommended hygienic, USDA-approved ERD25 rod-style electric cylinders with the ball screw/nut option. These electric actuators deliver greater filling accuracy and faster speeds than the previously-used pneumatic cylinders. Plus, the new motion control solution eliminates the need for a pneumatic system. The new linear motion system has fewer components and is more energy efficient.

ERD electric cylinders are clean-in-place compatible and feature a smooth, water-shedding, stainless steel housing and motor enclosure. The USDA-approved actuators are rated IP69K and can withstand even caustic washdowns without needing additional shielding.

ERD electric cylinders

ERD_SS2_and_USDA_features.jpgERD electric cylinders are well-suited to food and beverage processing. The ERD family includes the SS2 ERD10 (rated IP67), the SS2 ERD15 and ERD20 (IP69K) as well as the IP69K, USDA-approved design in three sizes (22, 25 and 30). IP69K models are washdown-ready and clean-in-place compatible. They don’t need shielding, which means streamlined machine design and reduced cost.

ERD actuators can be paired with many stepper or servo motors to create flexible, powerful, cost-effective electric actuator systems.

Download our ERD series catalog here. 

ERD Catalog

Learn more

Download our white paper: Evaluating actuators for washdown in food and beverage applications.

Evaluating linear actuators  for food and beverage  processing

Topics: Actuator selection, Actuators in Food and Beverage Processing