Duty Cycle and Electric Actuator

Today, the humanity stands in the borders of the fourth industrial revolution. It is more likely that an ordinary person has no idea of another three generations of technological breakthrough. Nevertheless, they have already passed. The current state of affairs can be characterized by one word – digitalization. Still, that stage has not achieved its peak yet. Besides, a plenty of mechanisms and devices originated from the third and second generations are still implemented in multiple areas of life and industry.

The present article is dedicated to a device called electric actuator and one of its characteristics. Generally, this mechanism is the upgraded version of its mechanical ancestor. The latter, in turn, can boast of a long history. Electrification gave birth to replacing versatile manually driven operations with automated analogs. Thus, there is no need to rotate a wheel or pull a lever to move an actuator while an electric motor can do it for you.

If you think that you have never encountered such technology in your life, you might be wrong. Examples of successful streamlining of electrically driven actuators include a dentist chair, lifting table, TV lift, sliding doors, and even a PC DVD-drive. As you can see, the scope of application is rather wide due to specific benefits of such type of actuators. Yet, the present publication mostly relates to a certain characteristic that can be found in the specification. It is referred to actuator duty cycle. As a rule, it is expressed in percentage points or timing data and remains unclear for many users. Hence, we will try to explain the principle of this notion and help you understand the importance of the said value.

What Is a Duty Cycle on Actuator

The general definition of term “duty cycle” denotes the proportion of operating time and resting time of a device. Otherwise speaking, this value shows how much time is required for ON and OFF modes. Concerning electric actuators, the timing is essential to avoid overheating of the motor. I.e., the said characteristic is a key to ensure performance and longevity of the mechanism. Correspondingly, exceeding the duty cycle of motor entails versatile defects and failures in operation including loss of power and subsequent death of the motor.

Duty cycle

Understanding of this characteristic is easier through an example. If you see the value of 10%, it may denote that 18 minutes of cooling down is required after 2 minutes of continuous operation. However, the timing may also be 4 minutes ON and 36 minutes OFF. It is probably that that example raised more questions than answers. Hence, let’s take some more practical situation.

To Understand Duty Cycle Better Let’s Take Example From Life

We were thinking a lot what would be a suitable analogy taken from life to explain the said characteristic in a clear way. Fortunately, we came across a decent example based on the principle of cycling. Indeed, this idea is great to show how one can comprehend duty cycle of linear actuator. That’s how it looks like.

Riding a bicycle consists of periods of peddling and coasting. In the first case, you exert energy, while the second case foresees movement with no efforts applied. So, these two modes change each other during the entire route of your ride.

The notion of duty cycle can be described within the borders of such example as the proportion of peddling period to the entire time of the ride. For instance, you spent half an hour with around 20 minutes of peddling to cover the entire route. In this case, the characteristic is almost 70% (66% to be accurate). It means that you are capable to peddle more than a half-way and need around 10 minutes for coasting in total. In the world of electronic equipment, such characteristic is usually less than 50%. The reason is that electric motors require more time in the OFF mode to get cooled. Now, when the concept is understood, we can shift to the calculation principle.

Duty Cycle Calculation

Those who are not good at math will appreciate that only two variables are needed to calculate duty cycle. These include the time in ON and OFF modes. Hence, we will indicate these variables correspondingly as N and F in the equation. The sum of N and F is the total cycle of exploitation. And that sum is the denominator of the duty cycle (D) ratio. The numerator is represented by the ON mode only. The duty cycle formula looks like as follows:

D = N / (N + F) * 100

One may have a reasonable question “Why do we need that equation if the duty cycle is usually specified?” The answer lies in the application of the equation. I.e., you need to learn the off time of your actuator based on the available data. Knowing two other variables allows you transform the equation as follows:

F = N / D * 100 – N or N = D * F / (100 – D)

Using the formulas above, you can calculate either the resting time if the operating time and duty cycle are known or vice versa. Let’s solidify this new knowledge by making some calculations with the specification of the actual product.

Example with Our Actuator

As a sample, our high speed linear actuator was chosen. The product is available with a customizable range of stroke (1 to 24 in), three force versions (33, 22, and 11 lbs) with the appropriate speed value (3.15 in/sec for 33, 5.51 in/sec for 22, and 9.05 in/sec for 11). However, these characteristics are useless for our calculations. At the same time, the duty cycle of actuator is what we need. High speed actuator can boast of 20%.

For calculations, let’s take the most powerful version (33lbs) with the longest stroke (24in). According to the specification, the speed is 2 inches per second at full load. Hence, it takes 12 seconds to get a full retraction. Now, let’s see how much time is needed to let the actuator OFF.

F = N / D * 100, where N = 12 sec, D = 20%.

F = 60 sec.

If we turn figures into words, we will get that after the full retraction of actuator. One minute is required for cooling down. After that, another work cycle can be performed.

Those who prefer a less powerful model (22lbs) with smaller stroke (16in) will have other figures. The speed at full load is 4 inches per second. Hence, 4 seconds is enough to complete the work cycle. The off mode requires 20 seconds only.

Now, it is time to explain why all that matters.

Does Duty Cycle Really Matter?

Heat can become a serious factor to damage any kind of equipment including linear actuators. The allowable meaning of heat is identified by the component with the lowest temperature threshold. As a rule, it is motor. For this reason, the duty cycle parameter is established to prevent overheating.

Duty cycle calculation is effective at a consistent pace of the entire running. The parameter is less effective for applications with infrequent actuation. It is not always possible to get an accurate reading. Understanding the said value allows determining an acceptable time for both running and resting. So, the motor remains within temperature limits. If the heat threshold was accidentally overcome, most actuators are equipped with thermal overload protection to shut down the device at a critical temperature.

So, the answer to the question is yes, it does matter. Put simply, users need the said value to control the operation time. Such control is a prerequisite for longevity and reliability of the device in use. On the other side, neglecting the recommended time frames for operation and cooling down can result in malfunction.

Recommendation How to Work with Duty Cycle

From theory to practice. A lot of fundamental conclusions regarding duty cycle of electric actuator and its importance were introduced above. Still, the most significant thing is a guide how to implement all this information in practice. Otherwise speaking, people need to know how to ensure stability and durability of operation. In fact, everything is quite simple. The principal rule is not to surpass duty cycle.

Compliance with manufacturer’s recommendations is the key to successful operation. However, the offered duty cycle is now always an appropriate value. What can be done in that case? The increase of the value can be the option. However, it entails the reduction of speed or force or both parameters at once. The opposite situation is observed when you need to enhance these key parameters.

SEE ALSO: How to Protect Linear Actuator: IP Rating and Advices

Most users follow the recommendation on the edges i.e. they deploy a device in full providing the achievement of the specified threshold at each working cycle. In other words, if an actuator has a 30% threshold, each running fits the value sharp (no more and no less). Such way of production run is also harmful since it reduces the durability of the device. In that case, it is recommended to find a more appropriate device with increased operating cycle (35% will be quite enough) or make sure that your machine is not applied constantly at breaking point. Provide a comfortable utilization of your equipment to have no problems with its maintenance in the future. This is the success formula.

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