Friday, 17 March 2017

How To Limit Travel On Linear Actuators Without Adjustable Limit Switches

Though we carry more micro-linear motion products than anybody, there are times when our customers have a stroke-length requirement that we cant fill with an off the shelf product. We do not offer linear actuators with adjustable limit switches, but there are plenty of ways to get the stroke you need.

The ability to adjust the stroke of an electric linear actuator for greater precision is incredibly useful. There are hundreds of applications that might require a custom stroke including:
  • Micro robotics applications
  • Opening and closing drawers and cupboards for home automation
  • Animatronic displays
  • Industrial or medical applications with tight tolerances
  • Automotive customizations
  • RC applications such as air brakes, landing gear, flaps or retractable canopies

Though are some linear actuators with adjustable end-limit switches, most are non-adjustable. We're going to walk through what you can do to get the custom stroke linear actuator that you need.

There are three ways to adjust the stroke of a linear actuator.
  • Adjust the actuators extension and retraction
  • Adjust on the retraction
  • Adjust only the extension.
Before you get started with a custom linear motion system, consider whether it might be easier to modify your project. Sometimes simply adjusting a mounting point could net you the same result as any of the below solutions. If you're sure that you need linear actuator with adjustable end-limits, keep reading.

What Are limit Switches?

There are many different types of linear actuators.  The simplest of these (such as our S series) have end-limit switches. Limit switches simply stop the actuator when it reaches it's end of stroke when retracting or extending.

There are both adjustable and non-adjustable limit switches, with the non-adjustable type being far more  common.

If an actuator does not have end-limit switches, or another means to shut down power at the end of it's stroke, damage to actuator is certain to occur as it will keep trying to drive until it burns out the motor or causes some other physical damage to the device.

Stall Protection

Stall protection is a feature found on Actuonix "R" and "I" series micro linear actuators, as well as "P" series when used with our Linear Actuator Control Board. It's similar to end-limit switches in that it stops the actuator from driving either in or out.  The difference is that while end limit switches are a physical stopping point, stall protection is a safety feature that kicks in when the motor 'stalls' or meets a certain amount of resistance.

If you need a linear actuator with a custom stroke length, you have options. You don't necessarily need a linear actuator with adjustable limit switches. Below are 5 options to get the custom stroke you need.

1. Use an LAC (Linear Actuator Control) board



Using a "P" series actuator with an LAC board increases the functionality of the actuator. One of the features it offers is the ability to set custom end-limits on both ends of the stroke. It's as simple as turning two pots to the desired position and then disconnecting and reconnecting power to the board. 

The LAC board is not only simple to use, but it's affordable. When you buy a "P" series actuator, we offer the LAC board for 1/2 price, which is only $20. For most applications, this is going to be your best bet for custom end-limits.

2. Use an RC radio

Our "R" series linear servos, are a direct plug-and-play replacement for rotary hobby servos. If you're  controlling your project via RC, you can set custom end of stroke limits in most modern radios. I use a Spektrum DX8 and it offers this functionality.

3. Install an external limit switch kit


An external limit switch kit is a small mechanical switch that will either make or break a connection when contacted by the actuator at a certain point.  You to set custom end limits on an "S" or "P" series actuator. It's inexpensive and relatively easy to install. If you need help installing an end limit switch kit you can find the data sheet here.

4. Use an arduino

This might work well for you if your project is already using Arduino. It's more complicated than simple limit switches or even using an LAC board. I won't cover this in detail here as there are several ways to accomplish custom end-limits with Arduino and that's a whole article on it's own. For support  using  Arduino with micro linear actuators, I highly recommend signing up for the forums at Arduino.cc.  There are lots of great, helpful Arduino users over there.

5.  Order a custom product

If you need a large quantity of actuators, it would be a big task to install limit switches on them all. We can help you out by building you a custom micro linear actuator with limit switches set to your specifications.

This would require a quantity order of at least 500 units. If you need a lot of actuators for an OEM product than this is a great, cost effective way to get the custom stroke that you need.

These are the top 5 ways to limit travel on electric linear actuators with non-adjustable limit switches. There are other options for limiting travel on electric linear actuators with non-adjustable  limit switches.  These however, are the simplest and most cost-effective for most individuals and companies.

If you have any questions about using a micro linear actuator with a custom stroke feel free to contact our sales department weekdays from 7:30am to 3:30pm.



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