Selecting Actuators

Size Does Matter…

Dear MISUMI Engineering Team:

We have several linear motion setups in our production line, with a variety of actuators. We’ve experimented with belts, ball screws, and lead screws in the past, but haven’t been able to find something that always works. We know we are oversizing actuators in certain cases, but it seems to make sense to use the same setup on our entire line for ease of maintenance and replacement. So are we doing the right thing, or are there other things we should be considering?

George P.

 

George, great question! First, there are several reasons not to oversize your actuators:

  1. A larger actuator will cost more, and requires higher maintenance costs.
  2. A more powerful drive has the potential for breaking or wearing down other parts, such as guides or linkages.
  3. The physical size of the drive can also become an issue when designing or upgrading a machine – it might be too big for the space.

Having the same drive on all your machines may look good on the surface; however, you need to factor in the wear and tear the larger actuator is causing your other equipment. Guides and drives can fail sooner than anticipated because of the additional forces. Also, you will have to look at your mounting hardware and brackets to make sure they are sturdy enough to bear the stress. In the end, while it may be convenient, you will probably spend more time fixing the problems, rather than enjoying the benefits, of having one size of actuators.

You mentioned that you’ve looked at other drive options. Each type of drive has specific advantages and disadvantages:

  • Ball screws have excellent positioning accuracy, a high thrust potential, and great mechanical efficiency. However, they are relatively slow.
  • Lead screws are not as accurate as ball screws, but have a superb repeatability and low noise level.
  • Belt drives are very quiet while providing unsurpassed speed and acceleration at the expense of accuracy.

Remember to carefully weight each design requirement against the different types of drives and to pick the best overall match for your system.

belt image
Belt image from
Misumi

Changing the type of drive you are using can also change the required actuator size. If you are currently using a lead screw, converting to a ball screw or belt if you are able will allow a small actuator because the mechanisms are more efficient at moving loads. The efficiency difference between ball screws and belts can be minor, so it’s best to look to other requirements when making a decision.

Lead Screw
Lead screw image from Misumi

You may still be wondering if a small thing like actuator sizing and type is going to make a difference in the long run. We would say absolutely! As more and more competition comes into the marketplace, companies will be forced to find the cheapest and easiest method available to stay in business. The days of over designing without a care are quickly falling to the wayside, and engineers and designers need to recognize this driving force and do their part in providing a profitable solution to a persistent problem.

 ball screw
Ball screw image from the Cambridge-MIT Institute

Have more questions? Leave comments below, or visit us here for access to software, selection software, or to configure products!

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