30 August 2019

Is it better to choose a pneumatic actuator or an electric actuator?

The determination of the operating costs for energy is - or rather should be - the fundamental step for a conscious purchase of the appropriate servo system for each application.

It should be pointed out that a feeding system can essentially consist of actuators that can vary according to the type of drive: pneumatic or electric.
Hence the age-old question: Is it better a pneumatic actuator or an electric actuator?

Is it better to choose a pneumatic actuator or an electric actuator?

Are the electric actuators all alike?

In fact, in the macro category of electrically driven actuators, it is good to distinguish between:

Traditional electric actuators, i.e. with a kinematics in which the rotary motion of the motor is transformed into linear motion of the actuator thanks to the presence of intermediate mechanical devices such as mechanical reducers, pulleys and belts, screws or pinions and racks.

Innovative electric actuators with "Direct Drive " technology, whose actuation system is direct type.

In the "Direct Drive" type actuators - Serialpicker is an example - linear motion is produced purely electrically and without wear by a linear magnetic motor. The linear motion, which occurs without contact, makes the use of intermediate mechanical parts unnecessary.

As you can easily imagine in the lack of intermediate devices, the kinematic chain is reduced. This leads to a cancellation of the reversal backlash typical of mechanical devices and consequently of traditional electric actuators, if we want to call them that.

Everything is relative

By this I mean that there is no category of actuators that by definition is always better than the others.
The decisive choice, in fact, depends on the type of application that an automatic machine is called to solve.

For example, pneumatic actuators are chosen based on their low acquisition cost. They are used in simple applications, where having two stop positions is sufficient. Of course, it is possible to obtain more stop positions, but to do this you have to insert a complex system of valves in the circuit. In this case, however, it has to be said that the repeatability that can be achieved is not at all comparable to the electrical fees.

Serialpicker linear units in SLIDE guide configuration

unità lineari e attuatori elettrici con motori lineari, Meglio un attuatore pneumatico o un attuatore elettrico?

But let me reason with you about something...

Presumably, within your company, you have used or are using - in your production machines, assembly machines or robotic lines - batteries of pneumatic actuators for mass-produced operations.

For the moment try not to consider the emphasis that the "future-proof" and technologically advanced solutions represented by linear motor actuators can give to your machines. Also try not to consider the unequivocal market trends that have seen the market for electric actuators grow five times over the last few years compared to pneumatic actuators.

Have you ever thought about how much you spend in terms of energy costs and maintenance costs of pneumatic actuators?

You should know that a recent study comparing total costs (acquisition, operation and maintenance) shows that electric linear drives, at current prices for components and electricity, are paid for themselves within a few months even for simple point-to-point movements with two end positions.

Is it better to choose a pneumatic actuator or an electric actuator?

Serialpicker, excels in point-to-point applications, even in cases of only 2 positions.

Let's make a comparison

Compressed air is without a doubt one of the most expensive energy resources, because compressors can only convert a small part of the energy input into useful energy.

The large majority is dissipated as heat loss
The latest technology allows to reach an efficiency of about 30%. Further increases are almost impossible, as the physical limits have been practically reached.

That's it? Not really...

In addition to the already high costs of the compressor, engine start-up losses and losses due to compressed air treatment, additional losses occur in distribution systems.
Actually, in the case of non-optimisation, after a further conversion, the amount of useful energy that remains available to the actuators is about 5% of the input energy produced.

No wonder, then, that in times of increased energy and environmental awareness (particularly concerning CO2 emissions), more and more companies are asking on their machines for the installation of electric actuators instead of pneumatic ones, especially in cases of medium and large production.

Energy and efficiency

Certainly an optimal design of the piping system and pneumatic actuators, rapid leakage and heat monitoring, the inclusion of recovery systems can increase efficiency.
However, pneumatic actuation remains a system that uses the energy produced very inefficiently, with an overall maximum achievable efficiency of 10%.

I'm certain you'll object at this point: "Yes, but electric actuators with linear motors have higher acquisition costs!

Of course, electric drives actually have a higher purchase cost than simple pneumatic cylinders and pneumatic actuators. But an analysis of total costs over their lifetime has shown that electric actuators and those with linear motors, in particular, as I mentioned earlier, can pay for themselves within a few months. This even in applications consisting of simple point-to-point movements or if you prefer between two simple positions.

Is it better to choose a pneumatic actuator or an electric actuator?

Operating costs and energy in €/year for 8000 hours of operation.

1294Pneumatic actuator bore 32mm
96Serialpicker module size 60

Here's an example:

Linear Actuator with horizontal stroke from point to point of 400 mm and 5 kg of moving mass, operating at 30 cycles per minute and with a duty cycle of 50% (= 2,000 ms cycle time).

Let's refer to Serialpicker size 60 module: the required positioning time of 500 ms is obtained with an acceleration of 10 m/s² and an average traverse speed of 1 m/s.

The acceleration time, during which the linear motor does useful work, is therefore 100 ms. This means that the actual energy absorption occurs only during one-fifth of the positioning time.

Energy consumption

When the motor is stopped and running at a constant speed, the motor does not absorb any more energy than is necessary to overcome friction. The kinetic energy that occurs during braking is converted into electrical energy by the motor (via the generator effect) and stored in special intermediate capacitors of the servo controller, where it can be used for the next cycle.

Assuming 8,000 hours of operation per year (three-shift operations) and an electricity price of 0.12 EUR/kWh. (price for large industrial consumers, including taxes, source EUROSTAT) the total annual cost of energy is 96 Euro. A pneumatic solution would be much more expensive, as we will see.

Serialpicker: the high-speed pick and place robot with linear motors

Meglio un attuatore pneumatico o un attuatore elettrico? serialpicker il robot pick and place con motori lineari

Is it better to choose a pneumatic actuator or an electric actuator?

Can you really save money with a pneumatic actuator?

As required by the application example, if a load mass of 5 kg is transported with a pneumatic cylinder at a (maximum) speed of 1 m/s, the analysis of the appropriate characteristic curves for the design of pneumatic cylinders by a well-known manufacturer indicates that a pneumatic cylinder with a 32 mm diameter piston should be used.

Unlike the linear motor, the energy (compressed air) must be fed into the motor during the entire movement.
The kinetic energy resulting from the braking of a pneumatic cylinder cannot be stored for later use but will be absorbed by the shock absorbers.

Consumption of a pneumatic actuator

According to its technical data sheet, the selected cylinder consumes 0.01047 dm³ of air at 6 bar per millimetre of cycle stroke. For a stroke of 400 mm, this translates into consumption of 4.188 dm³ per cycle.

At 30 cycles per minute, the pneumatic cylinder therefore requires a total consumption of 60,500 Nm³ of compressed air per year for continuous operation (8,000 h/year).
Considering start-up, load, reduction and handling losses, the compressor must compress and inject a total of approximately 80,000 Nm³ of air into the pipeline plant.

As you know, a normal compressor (750 kW motor, air flow 7,500 Nm³/h) can use 0.130 kWh of electrical energy to compress from 1 Nm³/h to 6 bar, including start-up losses and compressed air management.
The total annual cost of energy is therefore around 1,294 euro (0.12 euro/kWh*0.130kWh/m³*80,000 m³), or more than 13 times the operating cost of an electric linear actuator with an equivalent linear motor.
By increasing the size of the cylinder, this product would further increase the disadvantage of the pneumatic cylinder.

Last but not least...Do we want to talk about CO2?

Another huge advantage of choosing an electric actuator over a pneumatic actuator is the drastic reduction in CO2 emissions.
The energy of 10,000 kWh, required even by a single pneumatic cylinder in this calculation example, translates into an annual production of about 5,300 kg of CO2.

5.300 Kg per year!

Perhaps we should start to consider some changes...

Want a closer look? Request an appointment with one of our Technicians! !

Is it better to choose a pneumatic actuator or an electric actuator?
prodotti , , , , , , ,
About Massimiliano Milan
Massimiliano is an enthusiastic and passionate fan of snowboarding, technology, automation and robotics, in this precise order. Co-founder of Omas srl, he has 30 years of experience in the automation field.