Electric linear drives are a game changer

In addition to pure energy costs, the investment and maintenance costs must also be included in a total cost calculation.

Tests have shown that altogether they make up about 20 percent of total operating costs. In the example shown here, therefore, about 750 euros ($1500) must be spent on this each year, so the total operating costs add up to 3,750.

Manufacturers of pneumatic solutions rate the total costs (after energy efficiency measures) to be 0.025 euro per standard cubic meter of compressed air. For our example, this would result in total annual operating costs of 3,750 euros for the amount of 150.000 Nm³ of compressed air required for one cylinder, which supports the above calculation example.

A linear drive, including all required components (cables, inverter, etc.), in contrast, does cost more than a pneumatic drive (including valves, tubing, etc.). The significantly lower energy costs, however, mean that the electric drive pays for itself in less than half a year. After that point the savings are significant. The energy costs in our example exceed the investment costs for the pneumatic cylinder after just three weeks.

Analysis of the investment and energy costs in this application example shows that the savings from the use of an industrial linear motor, compared to the use of a pneumatic cylinder, are 2300 euros and 5900 euros at 12 and 24 months of service respectively.

Changing to an electric linear drive can also drastically reduce CO2 emissions. According to initial figures in 2011, the CO2 emissions factor for the power mix in Germany, with a high level of renewable energy content, was 559 g/kWh.

The 25,000 kWh that the pneumatic cylinder in the example calculation requires, relative to the 800 kWh/year for the electric linear drive, thus correspond to an annual increase of 13,360 kg of CO2 emissions.

If a German company replaces one pneumatic cylinder with one linear drive, an employee can drive his Seat Ibiza SC Ecomotive 1.4 TDI (98 g CO2/km) for 136,000 km, or the owner can drive his Ferrari 612 Scaglietti (470 g C02/km) for another 28,500 km at least, without degrading the company’s CO2 footprint.

Due to rising energy prices and the requirement for drastically reducing CO2 emissions, various providers have projects for increasing the efficiency of pneumatics. Considering the 30 times higher energy requirement in the concrete application example, however, it will remain difficult to even come close to the energy efficiency of linear direct drives.

Improvements of about 10-15 percent are possible for the compressor, but then the physical limits are reached. The leakage can be optimized to below 10 percent with appropriate effort. And even if the task in the application example could be handled with a smaller 32 mm pneumatic cylinder, the energy requirements and CO2 emissions would still exceed those of the linear motor by a factor of 12.5, or 1,250 percent.

When this is compared to the legal requirements for energy efficiency of asynchronous motors that went into force in 2011 (legal regulation for saving ‘only’ two to 22 percent), the magnitude of the difference in energy efficiency between pneumatics and linear motors becomes clear.

In addition to the lower energy requirements, the electric variant has the advantage of greater flexibility in the design of production sequences and monitoring systems. Motion sequences in electric linear drives can be significantly more dynamic and have higher repeatability.

The motion profile can be programmed freely, so that even complex motion sequences can be implemented quickly without a problem. They can also be adapted to new requirements, even during operation.

Linear drives are significantly quieter and more durable. They are not sensitive to changes in load and can be started and stopped smoothly. Analysis of the data produced in the inverter also allows various process variables to be monitored without additional sensors, which can also be used for remote diagnostics on the system.

Not least, fewer individual components are required, and they can be serviced and replaced much more easily than those used for pneumatics. This is reflected in lower costs for installation, maintenance, and logistics.

When more than two positions are needed, when motions are to be synchronized to a master shaft, or when the dynamics or service life of a pneumatic cylinder are no longer sufficient, the designer has for years gladly turned to linear direct drives from LinMot.

Due to high operating costs for pneumatics, the use of industrial linear motors pays off to an increasing degree, even for simple point-topoint motions with only two end positions. This is especially true when motions are performed regularly in cyclical operations, and pneumatic cylinders need to be sized generously due to speed and load conditions. In this case, the electric linear drive pays for itself within a few weeks.

Contact John Brooks, 0800 484950.