Selecting the Optimum Motion Technology for your Application Series: Lifetime

The next factor we will consider is the lifetime requirement of the motion system.  How many cycles must the motion system execute within the life of the product?  How many hours does that require from the motion system?

The first step is to translate the requirement of the motion system into a life target in hours.  The motion system has a job to perform which is typically defined in # of cycles per day and time per cycle or hours of operation per day and duty cycle of operation.  With these details, we can determine the approximate number of hours the motion system needs to complete:

# cycles per day * time per cycle (seconds) = Total time/day (seconds) / 60 / 60 = Total time/day (hours)

Or

Hours of operation/day * duty cycle (%) = Total time/day (hours)

Motion system hours = Total time/day (hours) * 365 (days) * product life (years)

Now that we know the requirement for the motion system hours, we can review our different technology options to determine which are appropriate for the application.  Brush DC motors have a mechanical commutation system that wears over time, limiting the lifetime of the motor.  Brushless DC and stepper motors are electronically commutated and therefore do not have any wear associated with commutation, making them have a longer expected lifetime than Brush DC motors. 

Another factor to consider for lifetime of the motion system is the bearing system.  Sleeve and ball bearings are options that are available with sleeve bearings providing a few thousand hours of life and ball bearings providing 10K+ hours of life.  This considers the radial and axial load applied to the motion system shaft staying within the limits designated by the specification.  If either load goes beyond the specification limit, the lifetime of the bearing system will be reduced.  The operating temperature will also impact the life of the bearing system, elevated temperatures while the motion system is running will impact the lifetime of the lubrication used in either bearing system.

The lifetime is a key requirement for the motion system in an application to ensure the expected warranty time is met.  Several factors have been reviewed above but considering them all together can become complex.  Portescap’s application engineers are available to review your application requirements to determine the appropriate motion system to meet your needs.