More than $30 billion is spent on electricity dedicated to electric driven systems, of which, nearly 70% goes to motor systems. There are ways to reduce this cost in your motion based mechatronics system.
By Alex Howe, Application Engineer
US WITTENSTEIN Group
Motor-driven equipment in manufacturing currently accounts for more than 2.3 quads, or 2.3 quadrillion BTUs (roughly 674 billion kilowatt hours) of energy use, which equals nearly 23% of all electricity sold in the United States. The U.S. Department of Energy has said that greater attention to motor system management can reduce motor energy costs by up to 18%. With these numbers, even small efficiency improvements can have dramatic economic, as well as environmental, results1.
These numbers help explain why nearly two-thirds of all motor systems selected today include energy efficiency in the specifications. OEMs have reported that the use of energy efficient motor systems boosts their overall productivity, reliability and profitability. As attention shifts from the mix-and-match potential of components to the importance of connectivity, engineering teams can make their choices based on each component’s value to the whole motion system.
Gear reducers are one of those components that can be sourced individually, but perhaps they should be evaluated with an entire system. With proper requirements analysis and system specification, the gear reducer can become one of the most cost saving components of a system.
In this power versus time graph, you can see that power savings from an appropriately sized gearbox increases directly with time.
The steps towards efficiency
It is vital that you be completely familiar with the application and the chosen motion system. Gear reducers are components that, if appropriately sized for the application, provide reliable, measurable efficiency as well as optimal performance. Two vital characteristics are necessary for correct sizing:
1. Choose a servo-rated gear reducer. At Alpha Gear Inc., we have developed a servo testing protocol, known as alpha cycle, from which we have derived servo-rated standards. The alpha cycle test determines the wear behavior under sinusoidal load in relation to run time. The ratings have been verified by leading servo motor manufacturers.
2. Use system analysis and servo sizing software. Only through in-depth analysis with software and application requirements can a gear reducer and servomotor be appropriately sized for the application. Let’s take a look at an example. We will compare an appropriately sized gearbox and an oversized one. In this example application, the system operates in a cyclical motion profile for one continuous month of operation (744 hours) and the energy cost is $0.1055 per kilowatt/hour2. For both gearboxes:
Nominal output torque = 33 Nm
Average output speed = 528.2 rpm
Three (3) year expected life with no maintenance required
The application is a belt and pulley drive with the following parameters:
Duty = 100% – back and forth movement
Load = 20 kg
Pulley Diameter = 80 mm
Cycle Time = 0.226 sec
Move Distance = 500 mm
We will use alpha’s cymex® servo sizing software to analyze this example. Application analysis through tools like cymex let you “try before you buy,” so you can fully examine such application specifications as motor use and gear selection. For this belt and pulley example, two gearboxes could be chosen depending on your comfort level of the validity of the catalog ratings:
The power versus time graph shows that the power savings from an appropriately sized gearbox increases directly with time. Energy cost savings in this application with a servo-rated gear reducer equals $87.10 per axis/per month.
This tangible cost savings highlights the importance of analyzing system components and using the right tools and manufacturers to create an efficient system.
A closer look at alpha cycle testing
Engineers at Alpha Gear have been testing theirs and other manufacturers’ gearboxes and servo gear reducers to the alpha cycle for nearly 25 years. The proprietary test scenario is a fatigue test, that is, it is an accelerated service life test, and it is the only industry standard for testing gearboxes.
The purpose is to test gearboxes to the maximum in realistic conditions. The engineers apply a sinusoidal load to the output of the gearbox and run this cycle for 1,000 hours. Application specifications are unique to the individual gearboxes tested.
Gearboxes that successfully pass the alpha cycle can be applied with confidence according to the ratings in their relevant technical documents.
Component selection is critical when analyzing system requirements. Before finalizing a design, it’s important to simulate full torque, speed and force behavior. Servo sizing software helps you choose system requirements and automatically gives you the optimal gear reducer and motor combination for the desired application. The capabilities to consider in gearbox selection include the inertia of the motor and the balance ratio in order to minimize the motor torque. The cymex® program helps ensure that the selected gearbox and motor match for optimal function and use.
Characteristic motor curve with application load.
Footnotes: 1. Consortium for Energy Efficiency, Inc., Motor Decisions Matter Energy Efficiency/Usage Fact Sheet, http://www.motorsmatter.org/press/energy_facts.html.
2. Average US energy rate, 2007, according to Energy Information Administration, http://www.eia.doe.gov
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