What Are the Factors That Determine the Lifetime of a Motor?
A customer who has been using motors for many years asked, "What are the factors behind a motor’s lifetime?”
What do you think lifetime is in the first place?
If it stops working, is that the end of its lifetime?
Not exactly. When the speed, torque, accuracy, etc., that are stated in the specifications can no longer be achieved, it has reached the end of its lifetime.
Figure 1 Change in Speed and Torque Due to Aging and Deterioration
I see. So the motor may be running, but it may be at the end of its lifetime.
That’s right. There are motors, gearheads, and circuit products, but can you tell me which components are responsible for the lifetime of these products?
I just studied about this the other day! For motors and gearheads, they are bearings and gears, and for circuit products, they are electronic components such as aluminum electrolytic capacitors.
Figure 2 Main Factors That Contribute to Lifetime
Well done, Vex. Now, I'll describe this in detail starting with the motor and gearhead. Bearings and gears are the parts that bear the most load when moving. Because they bear the load, they wear away by abrasion easily. In order to reduce abrasion, we use grease to make it slippery, but grease deteriorates due to heat.
Figure 3 Internal Structure of the Motor
I see, when the grease deteriorates, it becomes less slippery and they cannot perform to specifications.
That's right. But there is more than 1 factor that contributes to the lifetime. For example, there may be other factors such as lacking assembly accuracy or exceeding allowable inertia, so be sure to have them checked.
I got it! Can you teach me about the circuit products as well? What exactly does it mean when you say that an electronic component is an indicator of its lifetime?
In circuit products, the deterioration of electronic components start to affect the lifetime of the product. In particular, electrolytic capacitors store a lot of electricity and repeatedly emit electricity, so they bear a heavy load. These electrolytic capacitors also deteriorate under high temperatures, shortening their lifetime.
So, it's important to control the temperature rise not only a grease but also an electronic components. By the way, what amount of temperature rise will change the lifetime?
Bearing grease has the characteristic that its lifetime is reduced half for every 15 °C increase in bearing temperature. Electrolytic capacitors also have the characteristic that its lifetime is reduced half when the ambient temperature increase 10 °C.
Figure 4 Relationship Between Temperature and Lifetime
So how can we control the temperature rise?
There are ways to cool the heat source and ways to control the amount of heat generated by the heat source. You can see that the heat source should be cooled by a fan, right? So then, what do you think we can do to control the amount of heat generated?
Let's see...
You see, not all of the electrical energy input to the motor is converted into power. Some of the energy is lost, and this loss becomes heat.
I see! If the loss is reduced, heat generation is also reduced, and the temperature rise can be controlled. So we have to choose a motor with less loss... in other words, a motor with higher efficiency.
That's right. In addition to using a high efficiency motor, there is also the option of setting the current value according to the required torque for a stepper motor.
Make sure to review it. You'll be able to explain to the customer what you just learned about the relationship between heat generation and lifetime too.
Yes I can!
Lifetime is an important factor in determining the timing of maintenance and inspections for the customers' equipment. The Technical Reference describes the concept of lifetime for Oriental Motor products in detail. The estimated lifetime and the calculation are also listed, so be sure to check it out.
I understood! I will study to be a lifetime master.
