Questions You Should Know about Variable Speed Linear Actuator

An electric linear actuator is a device that converts the rotational motion of a motor into linear motion – that is push and pull movements. This way it is possible to lift, adjust, tilt, push or pull heavy or hard-to-reach objects, simply by pushing a button.

Additionally, actuators provide a safe, quiet and clean movement with accurate motion control. They are energy efficient and have a long lifetime with little or no maintenance.
Installing an actuator is very easy compared to hydraulic or pneumatic systems and it takes up much less space, as it has no pumps or hoses.

The ability of the actuators to adapt to specific needs ensures well-functioning solutions that are applied in many different aspects for a wide range of applications and products.

An electric linear actuator consists of a motor, a gear and a spindle including a nut. A special version of the linear actuator is the built-in actuator meant for integration in a customer guidance or linear column. A complete actuator system solution includes one or more linear actuators, a control box and a control device to operate the actuators.

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Lifting columns are designed to raise and lower to provide optimum ergonomics in a number of applications for the office, hospital & care sector and industrial markets. It is possible to connect a number of columns in parallel drive to provide electrical adjustability for heavy objects. The advantage of the column is that the linear guiding is built into the structure of the actuator and does not need adding externally.

Electric linear actuators are the perfect solution when you need simple, safe and clean movement with accurate and smooth motion control. You may choose actuator systems for adjustments, tilting, pushing, pulling and lifting with thrusts up to 10,000 N.

Actuators can be integrated into sophisticated control systems using data bus communication. You get precise position feedback and accurate variable control over acceleration and velocity.

Compared to both hydraulic and pneumatic systems an actuator solution is a lot easier to install. It takes up less space as there are no hoses and pumps that require routine maintenance to avoid safety hazards and messy oil leaks.

A linear actuator has a long lifetime with little or no maintenance at all. This ensures a very low total operating cost compared to other systems.
Electric actuator systems are quiet, clean, non-toxic and energy efficient. They fulfil the ever increasing demands and legislation concerning environmentally sound equipment.

Linear actuators move things. Some examples of practical automation applications are: sand, salt, and fertilizer spreader chutes;  throttle control, marine engine hatch, slide out steps, hoppers, hidden doors, solar panels, sliding doors, sliding window treatments, farming implementations and animatronics. Industrial applications include, damper control and height adjustable work stations.

The hydraulic actuator uses fluid to push a ram backwards and forwards, where as an electric actuator uses a DC motor to drive a lead screw, the lead screw is fitted with a nut that runs up and down the lead screw converting rotary motion into linear motion.

Dynamic, working, or lifting load is the force that will be applied to the linear actuator while it is in motion. Static load, also called the holding load, is the force that will be applied to the linear actuator when it is not in motion.

Linear actuators can be used in tension, compression or combination applications. Eccentric and side loading should be avoided. Please consult technical catalogues to ensure that all hardware used in conjunction with the linear actuator can withstand the maximum restraining torque.

Side loading, or radial loading is a force applied perpendicular to the linear actuator centreline. Eccentric loading is any force whose centre of gravity does not act through the longitudinal axis of the actuator. Both side loading and eccentric loading should always be avoided as they can cause binding and shorten the life of the linear actuator.

Linear actuators can be supplied with limit switches. The type of limit switches available varies with each product range, these include electro-mechanical, magnetic proximity and rotary cam. Limit switches (if fitted) are normally pre-set on actuators. Limit switches allow you the flexibility to set the limits of travel on your actuator to fit your particular application. The customer is responsible for properly setting the limit switch in the unit. If the limit switches are not set, or are improperly set, the unit may be damaged during operation. In addition, limit switches may require resetting if the translating tube of your linear actuator is rotated manually, as this will change the limit switch setting.

Linear actuators can be supplied with limit switches. The type of limit switches available varies with each product range, these include electro-mechanical, magnetic proximity and rotary cam. Limit switches (if fitted) are normally pre-set on actuators. Limit switches allow you the flexibility to set the limits of travel on your actuator to fit your particular application. The customer is responsible for properly setting the limit switch in the unit. If the limit switches are not set, or are improperly set, the unit may be damaged during operation. In addition, limit switches may require resetting if the translating tube of your linear actuator is rotated manually, as this will change the limit switch setting.

Linear actuators are available in a variety of linear speeds and a standard list is detailed with each product.

Duty cycle rating for a linear actuator is generally expressed as a percentage of “on time” (the ratio of on time to total time) or as distance travelled over a period of time. The duty cycle rating is expressed differently for different actuator types.

The linear actuators generally have a mounting option at the end of the ram and at the gearbox end of the actuator to allow a pivoting movement. There are a number of options, double clevis as standard, or clevis to trunnion. However all have multiple mounting options including clevis, trunnion, fork, top plate, base plate and threaded rod end.

Linear Actuators are either IP54 (NEMA 3) or IP66 as standard.

Unless otherwise stated back-driving is possible in all electric linear actuators. Actuators that use a ball screw are normally fitted with an electrical brake (typically motor mounted) to prevent the load from back-driving the actuator. Note if a machine screw actuator is considered self-locking, it may still back-drive if significant vibration and cyclic temperature variations are present. ACME screw or trapezoidal screw actuators would be considered to be self-locking.

Linear actuators are not recommended for use in applications where they can run into dead stops or can be jammed. Examples of jamming include over-travelling the limit switches and jamming the nut and screw internally at the extreme ends of the stroke or driving the actuator against an immovable object and thus overloading the actuator severely.

Improper loading, failure to set limit switches, excessive duty and extreme environments may contribute to premature actuator failure.

If actuators are run using a “Direct On-Line” (DOL) starting method then they can only be roughly synchronised for speed and position. Small differences in motor speed and actuator loading may cause the units to get out of synchronisation. The units cannot therefore be guaranteed to run in synchronisation. For exact synchronisation a closed loop control system is recommended. This can be achieved using AC motors with AC inverters or servo motors with a matched drive as part of a control solution. The speed and position feedback is typically provided by a potentiometer, incremental or absolute encoder. With DC motors a lead screw fitted encoder or a hall sensor can provide the closed loop feedback.

Linear actuators can be supplied with alternative materials and/or paint specifications for high corrosive areas. These options include stainless steel, chrome plating, electro-nickel plating or epoxy paint.

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Linear actuators are grease lubricated for the ram and gearbox assemblies. The actuators are greased for life except where a geared motor is fitted. This will need regular maintenance as detailed in the user guide.

Each actuator product range is fully tested to ensure long term reliability.

In the climatic test the actuators are tested to operate in extreme temperatures as well as to endure rapid changes in temperature. In some tests the actuator has to withstand going from a +100°C environment to -30°C repeatedly and still maintain full functionality.

In the weather protection test the resistance to both dust and water is tested.

The ability to handle relevant chemicals is tested by exposing the actuator to diesel, hydraulic oil, urea nitrogen, fertilisers, liquid lime etc.

What are the advantages of using Duff-Norton linear actuators over other linear motion solutions?

Duff-Norton linear actuators offer a packaged solution to your motion requirements. The integration of the actuator and motor simplifies the process of specifying and purchasing components for your motion system. Also, Duff-Norton linear actuators offer many advantages over hydraulic cylinders when low maintenance, installation and operating costs and environmental impact are considerations. Regardless of how simple your requirements or how complex, Duff-Norton Controls are available for all electromechanical actuators and can be customized to suit your application. In addition, Duff-Norton's application engineers can help you determine which actuator best suits your application and environment.

Can two or more Duff-Norton linear actuators be synchronized?

Tandem actuators can be used in certain applications. Small differences in motor speed may cause the actuators to get out of synchronization. Use of clutch models allows alignment when actuator is extended or retracted. Contact Duff-Norton application engineers to discuss your application.

What is the difference between static load and dynamic load?

Dynamic, working, or lifting load is the force that will be applied to the actuator while it is in motion. Static load, also called holding load, is the force that will be applied to the actuator when it is not in motion.

What's duty cycle and how is it calculated?

Duty cycle, measured in inches per hour, is the total distance an actuator may travel (extension and retraction) in an hour with equally spaced intervals between each cycle. Duty cycle may also be expressed as a percentage, which is simply the ratio of on time to total time (on and off time). AC actuators operate between no load and rated load with very little change in duty cycle. In DC models, duty cycle is approximately inversely proportional to load (percent of rated capacity).

Are Duff-Norton limit switches pre-set?

Duff-Norton does not preset limit switches on its linear actuators.Limit switches allow you the flexibility to set the limits of travel on your actuator to fit your particular application. Easy to follow instructions are included in the installation manual, and you may the factory if further assistance is required. The customer is responsible for properly setting the limit switch in the unit. If the limit switches are not set, or are improperly set, the unit may be damaged during operation. In addition, limit switches may require resetting if the translating tube of your actuator is rotated manually, as this will change the limit switch setting.

What are side loading and eccentric loading, and why should they be avoided?

Side loading, or radial loading, is a force applied perpendicular to the actuator centerline. Eccentric loading is any force whose center of gravity does not act through the longitudinal axis of the actuator. Both side loading and eccentric loading should always be avoided as they can cause binding and shorten the life of the actuator.

What are the "Dos" and "Don'ts" of mounting Duff-Norton electromechanical actuators?

Duff-Norton linear actuators can be used in tension, compression, or combination applications. Eccentric and side loading should be avoided. Please consult the technical data sheets to ensure that all hardware used in conjunction with the actuator can withstand the maximum restraining torque.

What are the most common factors in the failure of a linear actuator?

Improper loading, failure to set limit switches, excessive duty and extreme environments may contribute to premature actuator failure.

Can I adjust the speed of a Duff-Norton linear actuator in the field?

No, typical lifting speeds at various capacities within the operating range of each actuator are graphed on the technical data sheets. Should you have an application which requires lower speed, our application engineers can recommend another model or, if required, one that is customized for your application.

Can Duff-Norton actuators perform complex tasks?

Yes. Complex positioning tasks can be managed through the use of position feedback devices and electronic controls.

What does the clutch do?

The friction disk clutch in Duff-Norton linear actuators is set to slip when the rated load limit of the actuator is exceeded. This is to prevent damage to the actuator due to jamming, or overheating resulting from an excessive load. The load will be held securely should the clutch slip. The clutch also allows end of travel protection, but is not designed to be slipped repeatedly. Select a Duff-Norton actuator with internal limit switches or install external limit switches; if a clutch model will be slipped repeatedly.

Do Duff-Norton linear actuators require maintenance?

Maintenance is minimal but Duff-Norton recommends periodic lubrication to maintain optimal performance. The installation and maintenance guide will give you specific instructions for your model.

Does Duff-Norton make larger linear actuators?

Duff-Norton's linear actuators are rated for capacities up to 2,000 lbs. Duff-Norton also offers a full line of mechanical actuators with capacities up to 250 tons, motorized actuators up to 75 tons. In addition, Duff-Norton also offers customized controls that may be used in conjunction with any actuation system.

How can I determine which Duff-Norton linear actuator is best suited for my application?

Technical information pertaining to each model is contained in individual technical data sheets (see enclosed literature request form.)

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