Service Life, Expected Life, Estimated Life, MTBF

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Service Life, Expected Life, Estimated Life, MTBF

Postby om_tech_support_JT » Tue Aug 14, 2012 3:51 pm

Q: We use many of your products and have had success with them in the past. A customer of ours asked us to do a life time analysis on a custom pharmaceutical/pill dispensing machine that we build with your motors. I was wondering what information/specifications you can offer to help me determine the life of the motor. Any help would be appreciated.

A: We do show some reference numbers that you can use as an estimate of life. However, motor life is affected by a number of factors such as load, ambient/operating temperature, speed, operating requirements, and duty cycle. For the best analysis or estimate of life, you should test our products when it's installed in your machine with your load, environment, and operating parameters. Testing the motor without load, for example, can provide an inaccurate estimate.

For the reference numbers regarding service life of our products including motors, gearheads, and circuit products such as controllers and drivers, please click the link below. It will first show you a graph depicting the relationship between the motor bearing grease life versus motor case temperature. Since the ball bearing is the only component inside our motors that is susceptible to wear, and grease life is a critical factor, we use bearing grease life as the best estimate for our motor life. We will then show a table listing the rated life numbers for our gearheads. These numbers are based on operation within the product's specifications. We also show service life of a circuit product which is based on the life of the aluminum electrolytic capacitor inside our product.

For more details, please click: ... h_life.pdf

We also show some formulas to help you calculate your product life based on your own speed, load, and temperature parameters. Please contact us for assistance with these calculations.

In addition, we also show reference travel life numbers (in kilometers) for our motorized linear slide systems and motorized linear cylinder systems such as the EZS II series, the EZC II series, EZA series, SPV series, and PWA II series. The travel life of our motorized slide is determined from the maximum thrust force applied to the ball screw as well as the maximum transportable mass and moment load applied to the linear guide. The travel life of our motorized cylinder is determined from the maximum thrust force applied to the ball screw. Last but not least, we also show estimated life characteristics of our cooling fans.

If you take a look at the data we show, you would easily understand that the best way you can extend life of our products is to keep operating temperature low. Our AC motors would have either a thermal protection circuit to turn the motor off when it's too hot, or a high impedance winding that limits the increase in current draw, which limits the temperature rise. We typically want to keep the motor case temperature at around 60 deg C. This is considered normal saturated operating temperature. Anything over 100 deg C is considered detrimental to our motors. On our step motor systems, there are no thermal protection circuits, but you can lower the motor case operating temperature by adjusting a current-controlling potentiometer on its dedicated driver. By supplying less current to the motor, you are able to minimize operating temperature, but since current is also proportional to torque, you may have to use a bigger motor to accommodate for the torque loss. If you have problems reducing your operating temperature (such as inability to lower duty cycle), we can offer a high efficiency product which would help reduce the temperature without reducing your duty cycle, such as our AR series closed-loop step motor systems.

Let us know if you have any questions.

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