Linear actuators from Shift Automation - robust performance

Linear Actuator Resources for Senior Projects

First posted on shiftautomation.com

Using a linear actuator in your senior project

Movement is life.  It's much more complicated than that of course, but when we think of things that are full of life we usually think of something in motion.  And in our lives we are constantly moving or moving objects, whether it is walking up the stairs or turning the pages of a book.  Sometimes we wish that things would just move for us, like the escalator or automated doors that slide open (unfortunately without the satisfying Star Trek 'swish').  As budding engineers you have the opportunity to make things move.  

Linear actuators allow you to push or pull objects.  This could be pushing out or pulling in.

Push-PullYou could push or pull an object.

 

Push vertical Push Pivot
You could push up, or apply a force to a lever.

 

Pull pulleyYou could pull a cable under tension, this is a great way of changing the direction of force to physically fit the linear actuator into an application.

 

If you need linear motion, or to move an object with a pivot point, a linear actuator will provide the mechanism.  The challenge is to ensure the application of technology makes sense and is beneficial to the project.

If your project requires a linear actuator there are typically two ways you can go about incorporating one.  You can source the motor, threaded rod, drive nut, limit switches, and all associated couplings, required bearings, and any position sensors required.  The alternative is to buy one off the shelf and put more focus on solving the problem at hand, rather than engineering everything from scratch.  Buying a linear actuator is simpler and allows your project to focus on the real world problem you are trying to solve.

Automation is firmly rooted in current research and production environments, incorporating a linear actuator into your project will help further expose you to the use of automation to solve problems.

How to choose a linear actuator

When incorporating a linear actuator into your system you should consider the user experience.  How will your end user use what you are building?  Do you need just a manual rocker switch? Do you need intelligent control, by using position sensors in the actuator, external sensors (temperature, ultra sonic or IR proximity, flame detection, etc)?

By understanding how the end user will interface with your project you can determine if you need a simple switched system, remote control system, or a microcontroller to make decisions based on several inputs.  You will also be able to determine if you need an actuator with position feedback or no feedback.  

When choosing a linear actuator, you'll need to determine the stroke length and the force you require.  The stroke length is the distance of powered travel.  To make things easier for the lay-person, we've converted the force ratings of our actuators from Newtons to lb.  As an engineer, you know are more likely to work with Newtons when calculating forces.  A quick conversion is 4.45 * lb = Newtons.

The force you require can be affected by a number of factors.  If you are lifting straight up and down then the weight of the object is the force required, remember to account for friction and a factor of safety.

If you are moving a pivoting load, or your actuator is pushing or pulling at an angle, then you will have to break down the force into component vectors to ensure you have enough force in the direction you are trying to move.

How to control a linear actuator

If you decide to use a linear actuator in your project, you should think about who the user is, and the user experience you want to create.  You can just touch the actuator motor wires to the 12V power wires to make the motor go, but this is not an acceptable way to control the linear actuator for the end user.  It's fine when testing something out in the workshop, but not for a finished project.

When thinking about the linear actuator control you will want to determine if you will have a manual control such as a rocker switch, two individual buttons, or a wireless remote control, or a control with some intelligence.

If you decide your application needs some intelligence, where a simple switch or remote will not work, you can use a micro controller as the basis for a simple control system.  The control system and micro controller do not need to be complex; simple delays, checking for position, checking position of several components, these are all easily done and can make your project much more usable.  The main thing when deciding whether you are going to use a simple switch/remote control, or a micro controller, think about your end user.  Does the end user need to check if flaps are already open, or if there's something in the way of your moving component.  These are not user friendly, and other than the team building it, it doesn't make sense.  Design the control system so it's safe to use for people of varying levels of common sense.  If a manual rocker switch or remote control does this, then great.  If you need some intelligence to check for conditions, or you want finer control, then incorporate a micro controller.

If you choose a micro controller you'll soon find that you need some intermediate components to control a high current motor.  Typically this comes down to two options; relays or a solid state H-bridge.  Relays are simple, you can see how to wire up a couple SPDT relays to a micro controller here.  A solid state H-Bridge, motor driver, motor controller, are just as easy to use.  The benefit to using a motor driver is that you can control and vary the speed of the motor.  Motor drivers also quite often provide some basic information such as approximate current draw of the motor.

How to power a linear actuator

Most linear actuators have a 12VDC brushed motor.  Brushed DC motors typically have a tollerance for a range of voltages, so don't worry if your car battery outputs 14V.  There are a number of ways to power your linear actuator.  If you need a portable solution, you can use an automotive battery, marine deep-cycle battery, possibly with solar cell trickle charging.  You may also be able to use RC LiPo batteries either just one or two packs in series to boost the voltage, this depends on your system requirements.  If you run a linear actuator with less than 12VDC, your speed and maximum force will be reduced.

How to mount a linear actuator

 When it comes time to figuring out how to mount your linear actuator into the system, there are a number of ways to do this.  The easiest is to use prefabricated mounting brackets. If their design doesn't work with your design, then you may choose to incorporate mounting tabs and use a cross bolt to attach the actuator.  Another possibility is using a cable on the shaft and a pulley to fit a linear actuator into a tight space, and the pulley to change the direction of force.  This can give you a lot of flexibility in your design, but bear in mind that a cable only allows tension, not compression.

Ideas to incorporate into your senior project

I cannot stress this enough; the number one rule is to listen to your prof.  If your prof is asking for 'X' don't build 'Y' just because you think it's fun and all the cool kids are doing it. There's a reason they ask for certain criteria.  If you're lucky to have a prof that gives you a fair bit of latitude, then run with it.  Innovate, improve on an existing design, build something amazing. Some thoughts here if you're struggling for ideas, look at the world around you, in your community.  If you know of some accessibility struggles someone is having, try to figure out how to make it easier.  Engineers have the ability to improve the quality of life, use this.

And if your prof gives you lots of latitude in your project, build something unnecesary but cool.  Just remember to refer to rule #1 (listen to your prof!)